What is torque?
Probably the best way to start this is a simple explanation of what torque is - I'll start with the most common and useful measurement used, foot-pounds. This simply means what it says, feet times pounds.
If we put a 1 foot long wrench on a bolt and hang a 1 pound weight off the end, we would torque the bolt to 1 foot-pound. If we increased the weight to 2 pounds on the same wrench, we would increase this torque to two foot-pounds, or could achieve the same by leaving the weight at 1 pound and using a two-foot wrench.If we increased both, we would achieve 4 foot-pounds of torque.
It's that simple - torque is just good old fashioned leverage applied in a circle. It means the same thing on a bolt, on a car wheel, a steering wheel or a ratchet.
Why do we "torque" bolts?
Firstly, let me say we don't torque everything - things like tinware screws and small bolts should be simply snugged uo, but more on that later. Generally, we are tightening high-tensile bolts to a particular torque for very good reason.
So, first a little metallurgy. Those who studied mechanics at college may recall placing metal samples in a testing machine and running tests on them.While we will see tensile strength quoted on bolts, there are a number of important characteristics we need to know, the most important being the elastic range, plastic range, breaking strength and resistance to fatigue.
If we place a sample in the machine and start applying incremental amounts of tension (pulling force) we will find initially it will remain at the same length.At some point we will find the sample becomes longer under tension, then returns to it's original length when relaxed - this is the start of the elastic range. As we increase tension we will eventually find a point where the sample stops returning to the same length -it has permanently stretched. This is the start of the plastic range and if we continue increasing tension the piece will break, even if we keep replacing it.
If we repeatedly apply the same tension, then release it, we can test for fatigue - this means that eventually the piece will break, even though the tension never gets to the breaking tension determined above. At the lower end of the elastic range the number of repetitions required may be so high as to be meaningless, but toward the upper end of the range they may be relatively few, or the piece may stretch prematurely.
There are a similar set of characteristics for metal under compression, though of course they do not break and we usually alloys so that we remain within the rigid or minimally elastic range. And again there are characteristics for bending, but these do not concern us here.
When we choose a bolt or stud we aim for it to be operating within the safe part of the elastic range, taking into account any fatigue it might be subjected to. As we screw a bolt in, it will enter the thread of course. When the head contacts the surface and takes up any slack, it begins to place tension on the bolt. Knowing the angle of the threads, we can calculate what torque is required to provide this tension - providing everything was well cleaned and lubricated with oil or thread-locking liquid.
Some people, particularly tyre-fitters, think that putting more torque onto a fastener will make it stronger - in fact the reverse is more likely true! We can actually make up charts of the optimum torque on a particular diameter stud or bolt of a certain composition - though a little lower may be required for, say, a head stud in order to combat fatigue! If we tighten a fastener further into it's plastic range or where it will succumb to fatigue, we actually make the fitting weaker.
If you need to make a fastener stronger, you need to make it bigger, or of a different material! Making a stud longer means it will suffer less tension for the same increase in length, so does make it a little stronger. Making it thicker does of course make it stronger too - the reasons for not using the thicker 10mm studs on VW engines is for clearance around the spigot and pressure on the aluminium head due to the increased strength and less stretch. The head nut washers tend to pound into the head a little, but re-torquing the head a couple of times in it's early life should overcome it and is a good idea anyway. Periodic re-tensioning of VW head nuts is specified in the maintenace schedule, but failure to do this is a primary cause of engine failure -it's a bit of a hassle to remove the tinware and rocker shafts and besides, other engines don't need this, right?
As you probably don't have the ability to easily change the fasteners in your engine, I hope I have convinced you to purchase a quality torque-wrench or two and use it to torque things to manufacturers' recommendations.
- But how does that rate to the torque my Engine produces?
Torque versus Horsepower
While salesmen love to talk about horsepower, you may also have heard torque quoted for engines and maybe even heard that "torque is more important than horsepower" from people such as myself.
This is not quite true.
Peak torque is not much more important than peak horsepower. Torque is important - let me demonstrate with the example of a steam engine:
In a steam engine, we can multiply the steam pressure, in pounds per square inch, by the area of the piston face, to get pounds of pressure on the rod. We multiply this by the distance of the pinion from the centre of the driving wheel to get torque in foot-pounds. Experience gives us a percentage to reduce this by to account for friction and knowing the weight of the train we can easily calculate the maximum gradient it can climb.
The steam train has the advantage that this torque is available from standstill, providing we have enough pistons staggered around the drive axle, or the piston is in the optimal position. I have simplified things, but I hope you get the idea. The torque of the steam engine gradually drops off as speed increases due to restriction of how fast we can get the steam into the cylinder at the same pressure and eventually how fast we can produce the steam.
Our car engine does not reach it's maximum torque until it reaches several thousand rpm usuallythen this declines again. This due to the need to suck the air-fuel in, compress it and exhaust it and is affected by cam timing, intake and exhaust design and head choices. The stock VW engine made peak torque about 2000rpm and heavily modified one might not achieve this until 6000rpm or more.
Power is the rate at which energy is produced. A certain amount of energy is required to achieve a certain speed. A car of mass m will have kinetic (moving) energy of 1/2mv2 Joule at a speed of v , but will also require a certain amount of energy to overcome friction and air resistance. So power affects both how fast a car will accelerate and the maximum speed it can achieve.
The trouble is, the power an engine produces is also dependant on the speed of the engine - the example of the VW is producing 27hp at 2000rpm, rising to 47hp at 4000rpm, at the same time, the torque drops from 72 to 60 ft-lbs. While this amount of torque will still be able to pull up a steep hill at 4000rpm, the engine is capable of only accelerating about half as much at 2000rpm, yet it will spend more of it's time at this end of the range (less power = longer time to accelerate.)
A hopped-up engine tends to have it's peak torque higher in the range so unless a close-ratio gearbox or high-stall torque converter is used to keep the revs high in the range, this problem becomes much worse. An example bored and stroked engine with a fairly mild cam produces peak torque at 4250rpm and peak hp at 5250rpm - if we were trying to use it in the same range we would have 46hp at 2000 rpm and 113hp at 4000 rpm. Of course we can hold it in gear longer to the maximum of 142hp at 5250 but the ratio is now more than 3 to 1. More popular cams used on this engine combination can produce even higher hp of 160-170 at 6-7000rpm, but may end up with less than stock at 2000rpm!
This is why with a stock gearbox and diff ratio it is important to concentrate on having torque and getting it low in the range. Race cars can use low diffs and close ratio gears to keep those revs up and multiply torque -and aren't so worried about fuel consumption, wear or noise.
The "low" diff - it is important to point out that a diff called "low" actually has a high ratio, it is a low speed that is referred to - not only allows the engine revs to be held higher, it multiplies the torque of the engine. The gearing down provides leverage so that, ignoring losses, the torque out is increased by the same ratio that the speed is decreased.
In the same fashion, in order to be "close ratio" the higher gears need to be of higher ratio (lower.) As they are closer in ratio, the engine is changed to the next gear at a lower point and using a smaller range of engine speeds. As the engine is capable of higher revs, the car is not slowed by these higher ratios.
Friday, April 22, 2011
Saturday, January 29, 2011
Snake Oil for your VW
Some great sounding stuff you should pass by...
1. Teflon buttons. Sounds like a good, idea, but they are constantly rubbing against the piston walls, removing oil. They can also get damaged and leave pieces exactly where you don't want them. Circlip type snap rings work (install them the right way) and I have no reason to believe "Spirol lok" rings won't do what they claim. Put your trust in metal over plastic, or buy a rice burner...
2. High lift rockers with needle bearings. OK, I don't think they are around any more, but I couldn't leave this one out. About ten years ago it was hard to find after market rockers without needle bearings. Think about the action of the rocker, the pushrod is pushing up on one side while the spring is pushing up on the other. So the rocker is riding on just a few of these rollers for it's entire life - instead of spreading the pressure across the solid bearing, it is concentrated on a few very fine edges. Combine this with the fact that this design does not provide for adequate lubrication through to the valve end (if any) and oil tends to leak out of the roller bearing anyway these were a prety guaranteed way to shorten the life of your valve train.
3. "Magnetic" oils. These claim to be able to adhere to the engine in order to provide lubrication during startup, before oil is pumped up from the sump. Sounds like a great idea, but our engines rely on oil flowing across parts in order to provide much of our cooling - having a layer of oil holding heat onto the metal would be counter-productive. I have also heard from reliable sources that these tend to coagulate on the oil screen and can even clog filters. See my notes on oils, the thinnest oil our engine can cope with is a better bet for the VW.
4. PTFE (teflon) additives. Very popular when I was younger, and still to be found on the shelves in this day and age, when the jury is in. These additives do not stay long term where they are needed most, and have a high propensity for gathering where they are not - blocking the passage of oil to parts of bearings or even the engine, clogging oil screens and filters even sometimes causing pressure control valves to stick.
You can't drive a VW for very long without oil, no matter what you have put in it - it will overheat! And sieze - my poor 69 Kombi's engine died in less than 8km (that's about 5 miles in the old imperial measure.) Pistons, cylinders, crankcase, crank machining and a rod (clever VW-trained mechanic actually made up a "balanced" set from his spares,) all bearings of course.
5. Spark Plug indexing washers. OK, these aren't snake oil themselves, but some of the claims are. There is evidence you can get a little more power by pointing all your sparkplugs the right way - but you probably won't know which way that is for your particular engine. The other problem is that the required washer may be moving the plug further into the head than is optimum, exposing boss threads or shrouding the plug.
The main way these can be useful is if your plugs protrude too far into the head, exposing threads on the plug or maybe even getting too close to the piston. This may be due to wear, an overenthusiastic head job, or incorrectly made sparkplug (we won't name names here, but some of these were getting around a number of years ago.) Otherwise, concentrate on using quality plugs and make sure your deck height is low and combustion chamber well shaped.
6. Full Circle Crnankshaft. If you look at a stock crankshaft you can't help but notice that the arms for 1 & 4 in the middle are on the same side, as are the outer arms for 2 & 3. centrifugal force is pulling these out and as the engine is revved higher this is putting a bending force on the crank. A stroker increases both the weight and the length involved, magnifying the effect. To counteract this counterweights are added to the opposite sides of the crank on stroker cranks, or stock length designed for high rpm use.
In two stroke engines, the crankcase volume is used to pump the mixture into the cylinder, so a full circle crank can help top reduce volume and increase this effect. This does of course affect the balance of the engine and increase the rotating mass and books have literally been written on how to overcome these problems.
As every manufacturer soon realised they must add counterweights to their cranks, the problem was how to create a point of difference so people will buy your cranks? Some obviously saw what was being done in the two stroke and HD scenes and, not really realising (or caring) what the counterweights were for, decided that continuing them around the crank would be (or at least appear) better! One manufacturer, Bernie Bergman, even tried to counteract the increased mass by drilling holes on the counterweight side! Any increased strength in the crank would be offset by the increased imbalance and mass, resulting in a weaker than stock crank.
A variation on this that did actually appear to have some success on rebuilt stock cranks was to cut a counterweight which extended, while narrowing, up the opposing web to add strength. These apparently were a bit stronger than stock and did not have as severe an imbalance issue. The main concern here is the stresses put on the previously forged crank by the welding and re-machining - these days we can have a new counter-weighted crank forged from strong alloy in China for a lot less money...
1. Teflon buttons. Sounds like a good, idea, but they are constantly rubbing against the piston walls, removing oil. They can also get damaged and leave pieces exactly where you don't want them. Circlip type snap rings work (install them the right way) and I have no reason to believe "Spirol lok" rings won't do what they claim. Put your trust in metal over plastic, or buy a rice burner...
2. High lift rockers with needle bearings. OK, I don't think they are around any more, but I couldn't leave this one out. About ten years ago it was hard to find after market rockers without needle bearings. Think about the action of the rocker, the pushrod is pushing up on one side while the spring is pushing up on the other. So the rocker is riding on just a few of these rollers for it's entire life - instead of spreading the pressure across the solid bearing, it is concentrated on a few very fine edges. Combine this with the fact that this design does not provide for adequate lubrication through to the valve end (if any) and oil tends to leak out of the roller bearing anyway these were a prety guaranteed way to shorten the life of your valve train.
3. "Magnetic" oils. These claim to be able to adhere to the engine in order to provide lubrication during startup, before oil is pumped up from the sump. Sounds like a great idea, but our engines rely on oil flowing across parts in order to provide much of our cooling - having a layer of oil holding heat onto the metal would be counter-productive. I have also heard from reliable sources that these tend to coagulate on the oil screen and can even clog filters. See my notes on oils, the thinnest oil our engine can cope with is a better bet for the VW.
4. PTFE (teflon) additives. Very popular when I was younger, and still to be found on the shelves in this day and age, when the jury is in. These additives do not stay long term where they are needed most, and have a high propensity for gathering where they are not - blocking the passage of oil to parts of bearings or even the engine, clogging oil screens and filters even sometimes causing pressure control valves to stick.
You can't drive a VW for very long without oil, no matter what you have put in it - it will overheat! And sieze - my poor 69 Kombi's engine died in less than 8km (that's about 5 miles in the old imperial measure.) Pistons, cylinders, crankcase, crank machining and a rod (clever VW-trained mechanic actually made up a "balanced" set from his spares,) all bearings of course.
5. Spark Plug indexing washers. OK, these aren't snake oil themselves, but some of the claims are. There is evidence you can get a little more power by pointing all your sparkplugs the right way - but you probably won't know which way that is for your particular engine. The other problem is that the required washer may be moving the plug further into the head than is optimum, exposing boss threads or shrouding the plug.
The main way these can be useful is if your plugs protrude too far into the head, exposing threads on the plug or maybe even getting too close to the piston. This may be due to wear, an overenthusiastic head job, or incorrectly made sparkplug (we won't name names here, but some of these were getting around a number of years ago.) Otherwise, concentrate on using quality plugs and make sure your deck height is low and combustion chamber well shaped.
6. Full Circle Crnankshaft. If you look at a stock crankshaft you can't help but notice that the arms for 1 & 4 in the middle are on the same side, as are the outer arms for 2 & 3. centrifugal force is pulling these out and as the engine is revved higher this is putting a bending force on the crank. A stroker increases both the weight and the length involved, magnifying the effect. To counteract this counterweights are added to the opposite sides of the crank on stroker cranks, or stock length designed for high rpm use.
In two stroke engines, the crankcase volume is used to pump the mixture into the cylinder, so a full circle crank can help top reduce volume and increase this effect. This does of course affect the balance of the engine and increase the rotating mass and books have literally been written on how to overcome these problems.
As every manufacturer soon realised they must add counterweights to their cranks, the problem was how to create a point of difference so people will buy your cranks? Some obviously saw what was being done in the two stroke and HD scenes and, not really realising (or caring) what the counterweights were for, decided that continuing them around the crank would be (or at least appear) better! One manufacturer, Bernie Bergman, even tried to counteract the increased mass by drilling holes on the counterweight side! Any increased strength in the crank would be offset by the increased imbalance and mass, resulting in a weaker than stock crank.
A variation on this that did actually appear to have some success on rebuilt stock cranks was to cut a counterweight which extended, while narrowing, up the opposing web to add strength. These apparently were a bit stronger than stock and did not have as severe an imbalance issue. The main concern here is the stresses put on the previously forged crank by the welding and re-machining - these days we can have a new counter-weighted crank forged from strong alloy in China for a lot less money...
Sunday, January 16, 2011
Introduction to Heads.
- or, "The poor man's guide to fluid dynamics"
You have probably heard the claim before that the head(s) are the most important part of an engine build.
That's because it is true.
Unfortunately, it is also true that it is almost impossible to just go out and buy the right heads for your engine.
With the right headwork and a set of ratio rockers, an otherwise stock engine can outperform a significant percentage of "performance engines," possibly the majority! I have seen the dyno figures of engine making incredible amounts of horsepower through their huge (ported) heads, but usually only ever see one number. While the engine may be making 200HP at 8000 rpm, what is it making at 4000? Often it isn't even running well - this would be OK with close ratio gears and a low enough diff ratio, but with most VW transmissions this would run like a hairy dog around town! And drink like one, too!
I know I harp on about this a bit, but big ports and flow numbers do not equate to a powerful engine. Yes, the maximum or peak level of power an engine can make can be limited by, or enabled by the size of the ports, but if the ports are too large for the application, the engine may not be producing usable levels of power everywhere else in the rpm range!
People advertising heads often quote "capable of making xxHP" this is usually a calculation such as 1cfm @28" = 1HP which is kind of fair enough - but if the rest of the engine is not going to flow efficiently at that level there is no point. CNC machining has become affordable enough that the old "hog out the ports as big as you can get 'em" has found a whole new marketing strategy - but the mass-produced ports may not always be optimal, nearly always include completely removing the exhaust boss, and are too smooth for optimal flow. You heard me right - we actually learnt back in the 70's when flow bench data became available to the amateur scene (rally cars back then,) that a polished intake port flows less than a sand-cast one of the same dimensions! The same should probably be true for exhaust ports, but the reduction in heat transfer and coking of a polished port more than makes up for it - plus there is usually more room for enlarging the ports and a lower port velocity is not such a problem (exhaust gases commonly exceed the speed of sound, hence the sonic tuning.)
A careful examination of the figures in HTHRVWs shows that a stock VW port outflows a lot of aftermarket heads! Especially if a little sensible work is done on the combustion chambers after milling for larger cylinders and a good valve job performed!
The trouble with this is usually the cost of having someone with a flow bench perform the work, but the basic advice of HTHRVWs of unshrouding the valves, laying back the non-plug side and basic cleanup of the ports can be done by just about anyone and with a good valve job will produce good flow without decreasing port velocity (or increasing port volume) too much.
The original CB044 heads produced very good numbers from a port that was not overly large for most engines, but the extra metal around the combustion chamber and below the rocker and head studs left significantly less fin area for cooling. I didn't hear any stories of overheating however,but they are not available unported at the time of writing. A little unshrouding to the cylinder size on these or several alternatives such as CB041 or 043 heads should produce a good head. Without a flow bench it would be hard to be sure though.
Ok, so the work on the chamber in HTHRVWs makes sense to you and you are aware of the value of keeping the deck height, therefore squish volume, as small as possible while the port volume will set the compression ratio (either by porting or skimming) - what about the ports, huh?
Basically, we want the port size to be as small as possible while maximising flow. The main things here are to try to keep the cross sectional area constant, avoid any sharp bumps or turns, and avoid any "step" where the port suddenly becomes larger (or to a lesser extent, smaller.) We avoid the sudden steps by creating "venturi effect," essentially we smooth the change in and out to accelerate the air through the restriction. This enables to move air a little faster than the normal point where turbulence tends to occur, around mach 0.5, but only at that single point at the centre of our venturi. The required diameter can be calculated and you would be surprised just how small the optimum is for most engines when bore/stroke and rod ratios are combined with the appropriate cam timing - about that of a stock port or little more. An engine up to 2 litres turning up to 6k would most likely be happy with no increase in the maximum CSA of the port, just the appropriate cleanup as above. Strokers used on the street only require an average port diameter of 34mm to turn 6-7000+ rpm.
You can easily reach these engine speeds and flows using off the shelf CNC ported heads, but you will probably lose a lot of torque throughout the range. Remember, peak HP is what you are making at that RPM, torque is what you make the rest of the time (99% or more of the time.) Personally, I'd give up a little off the top end to get more for the 99% of the time when I really need it.
So, I'll probably get 041s with the correct bore and clean up the chambers. If they are no longer available I might get AJ Simms Pocket port. The Simms' have the advantage of the valve job already being done, but unfortunately he also takes the exhaust guide boss out and trims the guides.
Whatever heads you end up with, they will probably need some polishing not the intakes or exterior, the chambers and exhaust ports. This reduces heat absorption, coking and the risk of detonation. Smooth off any sharp angles or roughness with sandpaper or stones, then polish until you can see your face in it.
- and that was just the intro! At a later date I will put some detailed information here.
You have probably heard the claim before that the head(s) are the most important part of an engine build.
That's because it is true.
Unfortunately, it is also true that it is almost impossible to just go out and buy the right heads for your engine.
With the right headwork and a set of ratio rockers, an otherwise stock engine can outperform a significant percentage of "performance engines," possibly the majority! I have seen the dyno figures of engine making incredible amounts of horsepower through their huge (ported) heads, but usually only ever see one number. While the engine may be making 200HP at 8000 rpm, what is it making at 4000? Often it isn't even running well - this would be OK with close ratio gears and a low enough diff ratio, but with most VW transmissions this would run like a hairy dog around town! And drink like one, too!
I know I harp on about this a bit, but big ports and flow numbers do not equate to a powerful engine. Yes, the maximum or peak level of power an engine can make can be limited by, or enabled by the size of the ports, but if the ports are too large for the application, the engine may not be producing usable levels of power everywhere else in the rpm range!
People advertising heads often quote "capable of making xxHP" this is usually a calculation such as 1cfm @28" = 1HP which is kind of fair enough - but if the rest of the engine is not going to flow efficiently at that level there is no point. CNC machining has become affordable enough that the old "hog out the ports as big as you can get 'em" has found a whole new marketing strategy - but the mass-produced ports may not always be optimal, nearly always include completely removing the exhaust boss, and are too smooth for optimal flow. You heard me right - we actually learnt back in the 70's when flow bench data became available to the amateur scene (rally cars back then,) that a polished intake port flows less than a sand-cast one of the same dimensions! The same should probably be true for exhaust ports, but the reduction in heat transfer and coking of a polished port more than makes up for it - plus there is usually more room for enlarging the ports and a lower port velocity is not such a problem (exhaust gases commonly exceed the speed of sound, hence the sonic tuning.)
A careful examination of the figures in HTHRVWs shows that a stock VW port outflows a lot of aftermarket heads! Especially if a little sensible work is done on the combustion chambers after milling for larger cylinders and a good valve job performed!
The trouble with this is usually the cost of having someone with a flow bench perform the work, but the basic advice of HTHRVWs of unshrouding the valves, laying back the non-plug side and basic cleanup of the ports can be done by just about anyone and with a good valve job will produce good flow without decreasing port velocity (or increasing port volume) too much.
The original CB044 heads produced very good numbers from a port that was not overly large for most engines, but the extra metal around the combustion chamber and below the rocker and head studs left significantly less fin area for cooling. I didn't hear any stories of overheating however,but they are not available unported at the time of writing. A little unshrouding to the cylinder size on these or several alternatives such as CB041 or 043 heads should produce a good head. Without a flow bench it would be hard to be sure though.
Ok, so the work on the chamber in HTHRVWs makes sense to you and you are aware of the value of keeping the deck height, therefore squish volume, as small as possible while the port volume will set the compression ratio (either by porting or skimming) - what about the ports, huh?
Basically, we want the port size to be as small as possible while maximising flow. The main things here are to try to keep the cross sectional area constant, avoid any sharp bumps or turns, and avoid any "step" where the port suddenly becomes larger (or to a lesser extent, smaller.) We avoid the sudden steps by creating "venturi effect," essentially we smooth the change in and out to accelerate the air through the restriction. This enables to move air a little faster than the normal point where turbulence tends to occur, around mach 0.5, but only at that single point at the centre of our venturi. The required diameter can be calculated and you would be surprised just how small the optimum is for most engines when bore/stroke and rod ratios are combined with the appropriate cam timing - about that of a stock port or little more. An engine up to 2 litres turning up to 6k would most likely be happy with no increase in the maximum CSA of the port, just the appropriate cleanup as above. Strokers used on the street only require an average port diameter of 34mm to turn 6-7000+ rpm.
You can easily reach these engine speeds and flows using off the shelf CNC ported heads, but you will probably lose a lot of torque throughout the range. Remember, peak HP is what you are making at that RPM, torque is what you make the rest of the time (99% or more of the time.) Personally, I'd give up a little off the top end to get more for the 99% of the time when I really need it.
So, I'll probably get 041s with the correct bore and clean up the chambers. If they are no longer available I might get AJ Simms Pocket port. The Simms' have the advantage of the valve job already being done, but unfortunately he also takes the exhaust guide boss out and trims the guides.
Whatever heads you end up with, they will probably need some polishing not the intakes or exterior, the chambers and exhaust ports. This reduces heat absorption, coking and the risk of detonation. Smooth off any sharp angles or roughness with sandpaper or stones, then polish until you can see your face in it.
- and that was just the intro! At a later date I will put some detailed information here.
Saturday, January 15, 2011
Oils ain't Oils
The above is a quote from an ad we used to have here. It was very effective, even a little entertaining for a while, but it was wrong.
Oils is Oils - Synthetics aside,oil is dug up from the ground, base oils are essentially the same no matter who you buy from. The same fractions are used to produce particular grades. Some cheap oils are made from recycled oil, but the issue with these is how pure they are, not the quality of the base oil.
Grades is grades - If an oil is specified to have a particular grade, it will be made to meet that specification. Low quality reclaimed oils aside, the performance of the oil will be pretty much equal across various manufacturers.
Additives is additives - the base oil is the same, and in fact may be the same between a single grade and two different multigrades. The difference is in the additives. The main additive is the viscosity improver, which is what creates a multigrade oil. the base oil will actually be close to the viscosity that the single grade would have at high temperature, but special long-molecule additives cause it to not thin out at these high temperatures and increase it's shear factor, so it behaves the same as a heavy weight oil at this point.
Other additives are anti-oxidant, anti-corrosive and anti-galling (ZDDP.)
Old oils, as were originally specified for VWs, were single grade oils. It was necessary to have an oil heavy enough that it would not thin out too much at operating temperatures, while still pumping well and not gelling at the lowest temperature experienced. You may remember pouring such oils into engines, they were noticeably viscous, a bit like warm honey, while modern oils pour a bit more like water.
If the oil became too thin, it could not provide the lubricating barrier needed. VW, like most four stroke engines, use pressure-lubricated flat bearings. The bearing surface itself is quite soft as you may have noticed, it's main purpose being to hold a film of oil. If the crankshaft is perfectly balanced and the oil pressure sufficient, the crank should be spinning inside a thin film of oil, never actually touching the bearings. Of course, we don't live in a perfect world, so we rely on the shear force of/between the oil molecules themselves to prevent this contact. If the oil becomes too thin, it will not be able to maintain this facility. Another problem with thin oil, of particular concern to those of us running older style engines, is it will flow out of the bearings more easily, along with leaking from places that might not be such a concern with a heavier oil. This flow may cause problems with oil pressure, delivery to the extreme parts of the engine and possibly even the ability of the oil pump to deliver the required flow. The problems with oil leaks are fairly obvious, and the areas these tend to increase in this example are Head Studs, pushrod tube seals, flywheel seal and cylinder bases.
An oil that is too thick will not flow easily through the engine, making it slower to reach parts, and slower to return to the sump. It will not spray around as easily, hence will have reduced capability to cool the engine. it also will likely produce more friction.
Exotic Oils and additives:
The exception being the flush, of course. Just look at the crud in your engine when you do a rebuild and you will see this makes sense.
One more thing: A lot of people seem to have forgotten, or don't think it matters with modern cars/oils, but if you do not use your car regularly, do only short trips, or are storing the car you must do extra oil changes. Ever noted those interesting little indented patterns in your bearings? That is where acid has built up in the oil and sat there etching the bearings. This exists in all engines, but if the oil is not regularly reaching temperature or it is left for extended periods, such erosion becomes accelerated.
You don't need to change the oil again at the end of it's storage, just before. And if you only drive your car to the shops, enjoy a regular long drive, just to keep you both happy.
Oils is Oils - Synthetics aside,oil is dug up from the ground, base oils are essentially the same no matter who you buy from. The same fractions are used to produce particular grades. Some cheap oils are made from recycled oil, but the issue with these is how pure they are, not the quality of the base oil.
Grades is grades - If an oil is specified to have a particular grade, it will be made to meet that specification. Low quality reclaimed oils aside, the performance of the oil will be pretty much equal across various manufacturers.
Additives is additives - the base oil is the same, and in fact may be the same between a single grade and two different multigrades. The difference is in the additives. The main additive is the viscosity improver, which is what creates a multigrade oil. the base oil will actually be close to the viscosity that the single grade would have at high temperature, but special long-molecule additives cause it to not thin out at these high temperatures and increase it's shear factor, so it behaves the same as a heavy weight oil at this point.
Other additives are anti-oxidant, anti-corrosive and anti-galling (ZDDP.)
Old oils, as were originally specified for VWs, were single grade oils. It was necessary to have an oil heavy enough that it would not thin out too much at operating temperatures, while still pumping well and not gelling at the lowest temperature experienced. You may remember pouring such oils into engines, they were noticeably viscous, a bit like warm honey, while modern oils pour a bit more like water.
If the oil became too thin, it could not provide the lubricating barrier needed. VW, like most four stroke engines, use pressure-lubricated flat bearings. The bearing surface itself is quite soft as you may have noticed, it's main purpose being to hold a film of oil. If the crankshaft is perfectly balanced and the oil pressure sufficient, the crank should be spinning inside a thin film of oil, never actually touching the bearings. Of course, we don't live in a perfect world, so we rely on the shear force of/between the oil molecules themselves to prevent this contact. If the oil becomes too thin, it will not be able to maintain this facility. Another problem with thin oil, of particular concern to those of us running older style engines, is it will flow out of the bearings more easily, along with leaking from places that might not be such a concern with a heavier oil. This flow may cause problems with oil pressure, delivery to the extreme parts of the engine and possibly even the ability of the oil pump to deliver the required flow. The problems with oil leaks are fairly obvious, and the areas these tend to increase in this example are Head Studs, pushrod tube seals, flywheel seal and cylinder bases.
An oil that is too thick will not flow easily through the engine, making it slower to reach parts, and slower to return to the sump. It will not spray around as easily, hence will have reduced capability to cool the engine. it also will likely produce more friction.
Exotic Oils and additives:
- Magnatec, or similar products which claim the oil stays in place to protect your engine upon startup. If this process works, it will mean a layer of oil will be clinging to most parts of the engine, impeding the flow of cooling oil. I don't know if it is still true, but when these were first released they were also known for a kind of gelling effect, to the point where I have seen a stock oil screen effectively blocked. Maybe this factor has been fixed, but probably best kept out of air/oil cooled engines.
- Slick 50 or Nulon - PTFE additives. Very popular when I was young, with the tests showing a car driven for 500km without any oil! Even if you do try one of these products, don't try that with our air/oil cooled engine. These were also notorious for producing sludge, which in extreme circumstances could block filters or even oil passages. Scorched bearings where the PTFE had built up were also common. It seems no really scientific tests could back up their claims, unless they were paid for by the company in question... Again there is an added possibility they may interfere with cooling in a VW, so best to steer clear.
- ZDDP and Molybdenum Disulhphide. These are legitimate additives that produce wear resistance and anti-galling on surfaces that are under extreme pressure and/or temperature. These should be used as prelube on the valve train in particular, and can be used on most parts of the engine as appropriate (e.g. don't pre-lube the cylinders or valve stems.)
- Engine Flush - not really an additive, but something you should use. If you have just bought a second hand VW or engine, you will probably find the sump full of sludgy black muck from inadequate maintenance by the previous owner. Get as much out as you can, fill the engine with cheap oil and the flush and run per directions. Immediately drain the engine, leaving as long as possible, then fill with your regular oil. If the dipstick looks brown after a week, put another tin of flush through. Regular oil changes should suffice from here on if you are running air filters, but a flush every time the oil starts to look sludgy shortly after a change is probably a good idea. Additives will get used up or worn off - a clean engine will allow the oil to do it's job most effectively.
- Synthetic oil. Not so exotic these days. I will not go into detail here, but it seems the jury is in and synthetic oil is good for VWs... Except, I do not know of a fully synthetic oil that has a high enough base number for most of us, and the cost is prohibitive. If you want the benefits of a synthetic and are willing to pay the extra, 'cos you love your engine, use a good branded semi-synthetic. Of course I am talking about engine oil here - if you can find a suitable fully synthetic gear oil, use it - I guarantee you will enjoy the results.
- It's just a VW and I drive it. Use 20W50 if you can get it, you might get away with 20W40 if you live in a cooler climate, but if it's really cold you will be using a 15W- or 10W- The 50 means it will not thin out as much at temperature, and even healthy VW engines tend to run a bit hot. The 5W might look tempting if you want to go synthetic, but unless you live in Antartica will probably cause a lot of the problems described above.
- I've just rebuilt my engine, using German Seals and new crankshaft etc. Use 15W50, with similar warnings to above. If you have paid attention to bearing surfaces and sizes, bearing crush, etc, you should be OK with a 10W50 - I will try this when I get my engine done.
- I'm going racing - OK, now you are probably running an oversize oil pump, extended sump, high pressure hoses, etc. If you can afford it, run the fully synthetic as you want every ounce of power you can find - it may also help keep your monster cool. Don't run a single grade, even if you can get it, as your engine doesn't usually run long enough for it to get to temperature if you go to the drags, and will run too hot for it if you are an off-roader. If you are dropping your oil after every meet, you might want to save a little and run a semi-synthetic, but otherwise you probably can't afford the sport! Just kidding, lot's of people run dino oil in their drag cars for this very reason, just run the lowest base rating oil that won't leak all over the track.
The exception being the flush, of course. Just look at the crud in your engine when you do a rebuild and you will see this makes sense.
One more thing: A lot of people seem to have forgotten, or don't think it matters with modern cars/oils, but if you do not use your car regularly, do only short trips, or are storing the car you must do extra oil changes. Ever noted those interesting little indented patterns in your bearings? That is where acid has built up in the oil and sat there etching the bearings. This exists in all engines, but if the oil is not regularly reaching temperature or it is left for extended periods, such erosion becomes accelerated.
You don't need to change the oil again at the end of it's storage, just before. And if you only drive your car to the shops, enjoy a regular long drive, just to keep you both happy.
Valves
Run at 6 thou, run at 4 thou, run at 0 lash, but whatever is right for your engine - check valve clearance at least every 10,000km (6,000mi.)
If you, or your mechanic, do not do this religiously your engine will die young! If an engine is rebuilt, the valve clearance needs to be checked after the first start, after the first 20 minutes, then at 800 1,500 2,500 and 5,000km services (you do all those, don't you?)
All old pushrod/flat tappet engines needed their valve clearance checked and adjusted regularly, our VW just needed it a bit more often. Here's Why:
You can't check too often - some check weekly. If you keep this up, your engine will live a long life, if you don't it won't. Simple.
If you, or your mechanic, do not do this religiously your engine will die young! If an engine is rebuilt, the valve clearance needs to be checked after the first start, after the first 20 minutes, then at 800 1,500 2,500 and 5,000km services (you do all those, don't you?)
All old pushrod/flat tappet engines needed their valve clearance checked and adjusted regularly, our VW just needed it a bit more often. Here's Why:
- Air cooling. I am a big fan of air cooled engines (pun intended,) but they do tend to run hot - particularly where cooling is needed most, the heads. The hotter things get, the more they change size and the more prone metal is to stretching or fatigue.
- Pushrods - the aluminium in the pushrods can easily be pounded if lash is allowed to get too loose, this will generally cause the tips to recede into the rod, making it shorter, which in turn creates more lash, which then...
- Crankcase. Magnesium is wonderfully light and strong, but itself is rather soft, and alloying it to make it harder tends to make it brittle. Extreme cases of lash can make the lifter bores go out of round, causing noise, further wear, loss of oil pressure in the heads.
- Camshaft. Hopefully the cam developed a nice hard surface during the run-in, but a loose valvetrain can effectively knock the tops of the lobes, creating another spiralling wear pattern.
- Rockers. Stock rockers have a very small area of contact with the top of the valve stem, any excessive lash will increase their tendancy to hammer against it. "swivel foot" type adjustors can also be damaged by such hammering, in extreme cases rotating out of position and breaking.
- Valves. This is what it's all about - if the lash is too great, the top of the valve stem is being pounded by the rocker, if the lash is too tight, the valve will not be closing properly. The valves are also one of the reasons the lash changes - valves get mushroomed stems, they stretch, they pound themselves into seats and they wear. they are also often what causes the catastrophic failure of your engine if valve lash is not taken care of religiously.Specifically, it is usually No. 3 exhaust - the head breaks off, jams the piston, which then breaks the rod, etc. And it all starts with someone figuring checking and adjusting the valves is too much hard work!
You can't check too often - some check weekly. If you keep this up, your engine will live a long life, if you don't it won't. Simple.
Wrist Pin Clips and teflon buttons.
We call them gudgeon pins here, but anyway...
They need to be held in the piston, or they will walk out the end. The four most common methods of retaining them are:
1. Snap rings, or "stock circlips." These are kind of like a ring with the ends twisted in. To remove them, just sqeeze the ends togather with a pair of needle-nose pliers, swear and reach for an old screwdriver or such... OK, they aren't that bad - if one side is difficult to remove, the other is probably easy. They usually keep the pins in place too, but if the forces are great, the pin can push against the ends, which pulls the clip out of it's groove and hey, presto! Engine build time. This actually didn't happen all that often on stock engines that were properly looked after (though my friendly Volkswagen mechanic was familiar enough and the dealership he worked for used circlips.)
2. Circlips, these are pressed from sheet metal, and have holes for circlip pliers to get purchase in and remove (pictured.) These can be a little harder to remove, especially if they are installed backwards - "Hang on!" I hear you say; "backwards?" Yes, there is a right and a wrong way to install these. If you look at the profile, you will notice there is a bit of a chamfer from when they were pressed. The side that was on the bottom is a little wider and has sharper edges - this is the side we insert our circlip pliers from and will be on the outside of the piston when installed. You will note from the picture above, I have put one punched side up on the left and one "flat side" up on the right - the example on the right is how it will look to you from the outside of the piston. This is not only so you will be able to install them without finding why they are called dammit clips and also to remove them one day, this will give the greatest strength or retention. If they are installed the other way, extreme pressure could cause them to go concave enough for the chamfer to ride over the edge of the possibly worn groove and come loose. If they are installed as recommended, this same pressure will tend to push the ring outward, digging into the piston groove any more and they will not come loose in any normal engine operation. If they come loose after this, you probably have something seriously wrong with your engine - a very bad machining job on the case, or a dodgy crank.
3. Teflon buttons - the great high tech answer to you problem, without having to worry about details like installing things correctly! If you have a set, bin them. There is always going to be some kind of side pressure on the pin, which will be pushing at least one of these against the cylinder wall - the other will probably work it's way out there, too. These will then be constantly wiping oil from a patch of the cylinder wall, meaning a section of the piston and rings will not be properly lubricated and the cylinder will receive a little less cooling at this point. The buttons themselves are know for scoring the cylinder wall, though whether this is the actual button, or the above lack of oil, or grit and carbon building up on the button no-one can be sure. There may be a place for these in race engines that are rebuilt weekly, but leave them out of any engine you want to last - I have also heard of them disintegrating in turbo applications. The circlips work, they can be used in slipper skirt pistons, they don't interfere with pin or piston oiling and they are cheap. If you have already had Teflon buttons fitted, your pistons may be damaged beyond fitment of circlips, but you probably need new pistons and cylinders anyway.
4. Spirol-lok or similarly named products are actually like a helically-cut ring which is fed into the groove, then the pressure from the pin pushes them into a firmer position much like the circlip. I have not used these - circlips are cheap, they work and are easy to remove - but I see no reason why they would not be effective. My only concern with these would be removing them after the engine has seen a decent amount of work...
They need to be held in the piston, or they will walk out the end. The four most common methods of retaining them are:
1. Snap rings, or "stock circlips." These are kind of like a ring with the ends twisted in. To remove them, just sqeeze the ends togather with a pair of needle-nose pliers, swear and reach for an old screwdriver or such... OK, they aren't that bad - if one side is difficult to remove, the other is probably easy. They usually keep the pins in place too, but if the forces are great, the pin can push against the ends, which pulls the clip out of it's groove and hey, presto! Engine build time. This actually didn't happen all that often on stock engines that were properly looked after (though my friendly Volkswagen mechanic was familiar enough and the dealership he worked for used circlips.)
2. Circlips, these are pressed from sheet metal, and have holes for circlip pliers to get purchase in and remove (pictured.) These can be a little harder to remove, especially if they are installed backwards - "Hang on!" I hear you say; "backwards?" Yes, there is a right and a wrong way to install these. If you look at the profile, you will notice there is a bit of a chamfer from when they were pressed. The side that was on the bottom is a little wider and has sharper edges - this is the side we insert our circlip pliers from and will be on the outside of the piston when installed. You will note from the picture above, I have put one punched side up on the left and one "flat side" up on the right - the example on the right is how it will look to you from the outside of the piston. This is not only so you will be able to install them without finding why they are called dammit clips and also to remove them one day, this will give the greatest strength or retention. If they are installed the other way, extreme pressure could cause them to go concave enough for the chamfer to ride over the edge of the possibly worn groove and come loose. If they are installed as recommended, this same pressure will tend to push the ring outward, digging into the piston groove any more and they will not come loose in any normal engine operation. If they come loose after this, you probably have something seriously wrong with your engine - a very bad machining job on the case, or a dodgy crank.
3. Teflon buttons - the great high tech answer to you problem, without having to worry about details like installing things correctly! If you have a set, bin them. There is always going to be some kind of side pressure on the pin, which will be pushing at least one of these against the cylinder wall - the other will probably work it's way out there, too. These will then be constantly wiping oil from a patch of the cylinder wall, meaning a section of the piston and rings will not be properly lubricated and the cylinder will receive a little less cooling at this point. The buttons themselves are know for scoring the cylinder wall, though whether this is the actual button, or the above lack of oil, or grit and carbon building up on the button no-one can be sure. There may be a place for these in race engines that are rebuilt weekly, but leave them out of any engine you want to last - I have also heard of them disintegrating in turbo applications. The circlips work, they can be used in slipper skirt pistons, they don't interfere with pin or piston oiling and they are cheap. If you have already had Teflon buttons fitted, your pistons may be damaged beyond fitment of circlips, but you probably need new pistons and cylinders anyway.
4. Spirol-lok or similarly named products are actually like a helically-cut ring which is fed into the groove, then the pressure from the pin pushes them into a firmer position much like the circlip. I have not used these - circlips are cheap, they work and are easy to remove - but I see no reason why they would not be effective. My only concern with these would be removing them after the engine has seen a decent amount of work...
Paint your 'wagen
Another popular aircooled question, whith a lot of opinions, a lot of anectdotal information and bugger all science around.
It is well know in physics that a black item will radiate heat better than a silver one, but I think the first question is whether that is what we are looking for. The majority of heat energy is conducted away by air flowing across the fins, very little is radiated. Any paint or colouring is unlikely to provide a meaningful increase in heat dissipation in any case.
Bob Hoover pointed out the advantage of preventing rust, which he points out quite correctly is an effective insulator. I personally have not seen cylinders rusted to this degree, including my Kombi which spent most of it's life by the coast (and didn't have much metal left in the chassis, to be honest, but I was a poor student at the time.) Of course it looks good, so if you are of the "Cal-Look" crowd nothing else might matter and you need read no further.
Some guys here in Aus came up with a test rig which they claimed proved paint will make the cylinders run hotter, but there are a number of problems with their test method:
I would like to make some tests of my own at some point in the future, probably along these lines:
This still may not be repeatable to give reliable results. I recall when I was young there was similar debate about efficiency in heatsinks (used to cool electronic components.)
When a heatsink used in a non forced air situation was treated with anodising to make it black, there was little doubt there was an improvement and other tests showed advantages in painting (usually a very light coat from a common spray can of flat black.)
As soon as fan forced air came into the equation (and sometimes convection flow) the advantages would disappear in fact the efficiency of a painted heatsink was usually lower! The main reasons cited for this were usually insulating properties of the paint, or the reduction in turbulence from the smoother painted surface. Those cases where efficiency appeared higher with a painted surface could not be discounted as being from the surface preparation for the paint rather than the paint itself.
As an aside, producing a rough finish, a la Bob Hoover's blasting, does tend to improve the efficiency of either radiating or conducting surfaces, but you are unlikely to be able to measure the difference.
So, my opinion?
As anodising is not practical on cast iron, you are not likely to gain any improvement in cooling by painting your cylinders.
A thin enough coat should not cause any significant loss in cooling however, but such a coating may not be enough to prevent rust either. I'd probably try a combination of phosphoric acid treatment covered by a spray of highly-thinned flat black paint, or a straight (maybe tinted) zinc primer if I was going to try.
PS - I have to arguments with Bob Hoover's comments about chrome. It will significantly reduce radiant heat dissipation on valve covers and pushrod tubes and personally, I'd like to keep all the cooling I can get.
PPS - if anyone can afford gold plating, I'd love to know the results - or you can do it to my engine and I'll let you know.
It is well know in physics that a black item will radiate heat better than a silver one, but I think the first question is whether that is what we are looking for. The majority of heat energy is conducted away by air flowing across the fins, very little is radiated. Any paint or colouring is unlikely to provide a meaningful increase in heat dissipation in any case.
Bob Hoover pointed out the advantage of preventing rust, which he points out quite correctly is an effective insulator. I personally have not seen cylinders rusted to this degree, including my Kombi which spent most of it's life by the coast (and didn't have much metal left in the chassis, to be honest, but I was a poor student at the time.) Of course it looks good, so if you are of the "Cal-Look" crowd nothing else might matter and you need read no further.
Some guys here in Aus came up with a test rig which they claimed proved paint will make the cylinders run hotter, but there are a number of problems with their test method:
- The temperature sensors were mounted on the outside of the cylinders. The outside of the cylinders and the fins are where we want to transmit the heat from - a higher surface temperature could indicate more efficient cooling! (Refer Newton's Laws of Cooling.)
- The method involved filling the cylinder with water, then cooling it with a fan, which suggests questionable accuracy and repeatability.
- The sensors, I believe, were thermistors which are not the most accurate device (using accurate in the scientific sense.)
- The tests do not appear to have been performed a number of times.
I would like to make some tests of my own at some point in the future, probably along these lines:
- Drill a hole into the cylinder wall and insert a thermocouple, probably at more than one point and preferably out of the area exposed to the airflow, or inside.
- Heat the cylinder to a set temperature, probably in a similar way, as the boiling point of water is pretty constant, so the cylinder can be filled for a set period, drained and capped, and the temperature should be pretty constant.
- Simulate the air pressure, flow and speed of the VW fan.
- Monitor the rate of temperature drop of the actual cylinder wall under these conditions.
This still may not be repeatable to give reliable results. I recall when I was young there was similar debate about efficiency in heatsinks (used to cool electronic components.)
When a heatsink used in a non forced air situation was treated with anodising to make it black, there was little doubt there was an improvement and other tests showed advantages in painting (usually a very light coat from a common spray can of flat black.)
As soon as fan forced air came into the equation (and sometimes convection flow) the advantages would disappear in fact the efficiency of a painted heatsink was usually lower! The main reasons cited for this were usually insulating properties of the paint, or the reduction in turbulence from the smoother painted surface. Those cases where efficiency appeared higher with a painted surface could not be discounted as being from the surface preparation for the paint rather than the paint itself.
As an aside, producing a rough finish, a la Bob Hoover's blasting, does tend to improve the efficiency of either radiating or conducting surfaces, but you are unlikely to be able to measure the difference.
So, my opinion?
As anodising is not practical on cast iron, you are not likely to gain any improvement in cooling by painting your cylinders.
A thin enough coat should not cause any significant loss in cooling however, but such a coating may not be enough to prevent rust either. I'd probably try a combination of phosphoric acid treatment covered by a spray of highly-thinned flat black paint, or a straight (maybe tinted) zinc primer if I was going to try.
PS - I have to arguments with Bob Hoover's comments about chrome. It will significantly reduce radiant heat dissipation on valve covers and pushrod tubes and personally, I'd like to keep all the cooling I can get.
PPS - if anyone can afford gold plating, I'd love to know the results - or you can do it to my engine and I'll let you know.
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