Balancing P/C only

[Marc]

Please read this article it may help you change your mind...This engine is still running in a uk street car I believe.

I'll try one more time. The reason an ACVW crank, even a short-stroke one, benefits from the addition of the counterweights is not because of balance per se, it's because the two center crankshaft throws are offset to the same side of centerline. If there were two more main journals/bearings this would not be an issue, but since there are not it's only natural for the crank to flex like a jump-rope once the inertial forces overcome the stiffness of the forging. Even a stock Rabbit crank, which does have 5 main bearings, has counterweights because it's designed to run in a higher RPM range than the ACVW was intended for. There is an exception, the short-stroke cast crank used in the 1457, and it does work quite nicely in that application (even though the pistons are the same diameter and if anything are heavier than those used in the 1588) - but that's with a main bearing between every pair of throws, and stiff cast-iron block.

69mm stock Type I crankshaft:


This is a simple, straightforward FACT and I'm not going to "change my mind" about it based upon anecdotal evidence, but since you seem to be overly impressed by stories here's one for you:

The first circletrack class I ever competed in was limited to 1300cc - those pistons are considerably lighter than even the lightest 1600. You can be sure that my engines were dynamically balanced to within a gnat's ass by the most competent machine shop in the region.
Flywheels were restricted to a minimum weight of 16 lbs and counterweights were forbidden.
I ran the tallest gearing of any one competing and still exceeded 6500 RPM whipping around a 1/5-mi track in 2nd with 23" tires (those with "short" gears were buzzing close to 7500). The cases took the brunt of the damage, they'd be pounded out at the center main web to the point of being unserviceable in at most half a season's racing. And yes, shuffle-pins and other "fixes" were all tried with no positive results. EVERY team (at least every one that was running competitive laps) had the same problem.
Most everyone would "move up" after their rookie season to the 3/8-mi track where displacement was upped to 1650cc and carburetion was unlimited - engines turned harder and faster and longer yet they lived because in that class counterweighted cranks were legal. Many teams had a "spare" engine at the ready which was typically built from veteran components and seldom had a CW crank; they were used as a last resort, though, because one 30-lap feature was about as long as they were expected to last. I did build one engine with a stock crank that was used to set a track record (lower windage = more HP), but that was only run for three laps...

[Phil69]

Please read this article it may help you change your mind...This engine is still running in a uk street car I believe.

I'll try one more time. The reason an ACVW crank, even a short-stroke one, benefits from the addition of the counterweights is not because of balance per se, it's because the two center crankshaft throws are offset to the same side of centerline. If there were two more main journals/bearings this would not be an issue, but since there are not it's only natural for the crank to flex like a jump-rope once the inertial forces overcome the stiffness of the forging. Even a stock Rabbit crank, which does have 5 main bearings, has counterweights because it's designed to run in a higher RPM range than the ACVW was intended for. There is an exception, the short-stroke cast crank used in the 1457, and it does work quite nicely in that application (even though the pistons are the same diameter and if anything are heavier than those used in the 1588) - but that's with a main bearing between every pair of throws, and stiff cast-iron block.

69mm stock Type I crankshaft:


This is a simple, straightforward FACT and I'm not going to "change my mind" about it based upon anecdotal evidence, but since you seem to be overly impressed by stories here's one for you:

The first circletrack class I ever competed in was limited to 1300cc - those pistons are considerably lighter than even the lightest 1600. You can be sure that my engines were dynamically balanced to within a gnat's ass by the most competent machine shop in the region.
Flywheels were restricted to a minimum weight of 16 lbs and counterweights were forbidden.
I ran the tallest gearing of any one competing and still exceeded 6500 RPM whipping around a 1/5-mi track in 2nd with 23" tires (those with "short" gears were buzzing close to 7500). The cases took the brunt of the damage, they'd be pounded out at the center main web to the point of being unserviceable in at most half a season's racing. And yes, shuffle-pins and other "fixes" were all tried with no positive results. EVERY team (at least every one that was running competitive laps) had the same problem.
Most everyone would "move up" after their rookie season to the 3/8-mi track where displacement was upped to 1650cc and carburetion was unlimited - engines turned harder and faster and longer yet they lived because in that class counterweighted cranks were legal. Many teams had a "spare" engine at the ready which was typically built from veteran components and seldom had a CW crank; they were used as a last resort, though, because one 30-lap feature was about as long as they were expected to last. I did build one engine with a stock crank that was used to set a track record (lower windage = more HP), but that was only run for three laps...

A great story and information.
So how light where the pistons you used on your 1300's?
Some guys over here built a grass track engine (again std crank) they lightened the pistons so much that they could only run with one compression ring they set up and oil spray system to cool the back of the crowns so they wouldn't hole!
I guess that was my point I was trying to make (badly) is that counter weights on a flat four air cooled are not necessary for balance more strength. Saying that I have seen two instances of forged counter weight cranks sheering at the junction of the webs and journals.
Any idea why this would be?

I believe also Rabbit engines (we call them Golf's I believe) are a in line four not a flat four and are therefore dynamically different as you would know when it comes to balance weights having an effect on rpm's and piston and rod weight.

Sorry about the SI units guys European's huh and so all the measurements used are normally metric over here. I can and do work in inches and lbs but it's like banging your head on a metre of concrete.
Oh IIRC the picture you have posted is an early stock crank due to the single oil gallery drillings?

[Marc]

That's why I was questioning what you meant by "no real effect" - we agree that they are not required for balancing, but I can assure you that they still perform a very real function.

I don't recall the 1300 piston weights (that was 35 years ago) but they're 77mm diameter, so you can imagine how much lighter they are than 85.5s.

Yes, the Rabbit/Golf engine has different balancing/harmonic concerns and I probably shouldn't have brought it up...but the point I was trying to make is that it's crankshaft still has the two center rod throws offset to the same side of centerline, yet it is not as subject to the "whipping" effect because it is better-supported.

The crank in the picture is a non-crossdrilled, O-ring style...as used on mid`66 and `67 1300 and 1500cc engines. The additional oil passages to the rod journals debuted for `68. Earlier 69mm cranks were essentially the same, but weren't machined at the snout to accept an O-ring flywheel.

[nsracing]

for the rotating assemblies, you need a dynamic balancer to do the job.

for pistons and rods just a scale is needed.

if the pistons and pins are good manufacture like Mahle, I can tell you they are very close w/ pins. But pistons can very by a lot. so you need a nice scale to balance the pistons and/or rods.

Rods are balanced first the bigends ...make them all equeal. This is part of the rotating weight. The small end -reciprocating wt.- you just put the rod on the scale and make them all even. Take the weight off the small end.

Flywheel, pulley, crank, pressure plate all need to be spun on the balancer to figure out all the unbalances.

I do balance jobs when time permits. Let me know if I can help.