77MM Pistons?

[Veefan]

I'm selling some spare parts on e-bay, one item I have listed is a set of 77mm .020 over pistons.

Providing all the below rules are met, shouldn't they be legal?

The GCR says

"The engine shall be a standard VW power plant, as normally fitted
to VW sedans as defined herein. Any engine part(s), listed by the
manufacturer (VW) as a current, superseding, replacement part for
the standard VW 1200 series, Type 1, U.S. model sedan and interchangeable
with the original part(s), may be used."

4. Pistons and wrist pins minimum combined weight without clips
or piston rings = 330.0 grams

a. Maximum bore: 3.040 inches
b. Stroke: 2.520 inches +/ 0.005 inch.
c. Minimum capacity of combustion chamber in head: 43.0cc
(Polishing and/or tooling is prohibited.)
d. Minimum depth, top of cylinder barrel to top of piston:
0.039 inch


http://cgi.ebay.com/ebaymotors/ws/eBayI ... 0696652986

[FV80]

John,
No - they are not legal. VW has never defined the 0.020 over pistons as "replacement parts". I sent you an email a few minutes ago. VW HAS, however, just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). The pistons do not define "the bore" - the cylinders do that.

Steve, FV80

[SR Racing]

vw just notified SCCA that the newer aluminum cases are now official replacement parts for the mag cases (see Feb FasTrack). Steve, FV80

And a good idea if you need another 14 lbs of ballast. We have built some of the hyper Bug engines with them, but they are pretty heavy for FV.

[tiagosantos]

Are they cheap though? I could use the ballast!

[SR Racing]

About $100 more than a stock case. You can probably find 15lbs of ballast cheaper than that.

[tiagosantos]

Gee.. For that much money, I can probably EAT 15lbs of ballast!

[hardingfv32-1]

Is this new case extra strong, a rhino case?

Brian

[brian]

I know there are some heavy duty after market aluminum cases but aren't the new cases simply made of different material?

[hardingfv32-1]

So the 15 lb. might come from the loss of magnesium?

Brian

[DanRemmers]

The density of magnesium is about 1.74, and aluminum is about 2.8. So if the magnesium case saves 15 lbs, then it weighs about 25 lbs and the aluminum case weighs about 40 lbs.

[hardingfv32-1]

I did not appreciate that the case was pure magnesium.

Brian

[brian]

They weren't. The cases were a blend of materials. AS41 casted on the cases described the mix of materials. Cant remember the exact combination but the AS41 included zinc.

[smsazzy]

AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM

[FV80]

AS41 composition is 4.3% Al , .35% Mn , 1.0% Si , remainder MAGNESIUM

Hmmmm... 94% Mag - I think we can call that pretty much a Magnesium case .

Steve

[SR Racing]

The aftermarket AL cases also have larger webbing etc. They are quite a bit beefier.

[hardingfv32-1]

I'm looking for a more stable case to develop a zero clearance engine. This could be the answer.

Brian

[SR Racing]

Zero clearance? You mean like interference fit rods and main? We have acouple laying around if you want one.

[hardingfv32-1]

To be honest I'm not sure what it means. I have seen it used in a couple of places to indicate an engine that has very little clearance when cold. When the engine is at operation temperature the clearances are more like the numbers we normally use. I have cut my cold clearances in half so far. Working my way down until I get a failure. Very few crank grinders willing to or capable of holding the tolerances required.

Why? Thinner oil, less friction. Can now use 15W @ 240 deg with no problem.

Brian

[brian]

The tighter clearances also means higher oil pressure, doesn't it? Recent thinking seem to contend that higher oil pressure means more drag and less flow.

[hardingfv32-1]

No, the requirement for tight clearances is strictly to keep the oil from leaking out of the bearings and causing oil pressure losses. They are required to maintain normal oil pressure.

There is no drag penalty for tight clearances until you get metal to metal contact. Scientific studies have shown it is a complete myth about extra clearances being needed for a race engine. A free spinning cold crank assembly means nothing. How it spins when at operating temperature is what counts. Of coarse we are talking about a high maintenance race engine, not common idiot proof FV dune buggy examples.

More power the thinner the oil gets. Don't need the power extra power, then stick to the simpler dune buggy engines.

I have not studied the effects of high oil pressure because that in never an issue.

Brian

[brian]

Crank clearances for our motors is designed to prevent metal to metal events. It' s nice to think of our cranks as stable units but the truth is that they are really moving around in the case and if you don't have at least .002.5 on the mains you'll get contact.

I agree with you Brian that on our motors there's a ton of oil escaping the rod bearings and flooding the engine which should be reduced. But current thinking combined with recent developments in synthetic oils have shown that by reducing oil pressure, which is resistance to flow, increases life and hp. Flooding the bearings maintains film strength and will help prevent failures. All bets are off when one talks about dry sumps, evacuated crankcases and more modern engine designs.

[hardingfv32-1]

I'm not sure that our cranks move around. Regardless, thinner oil films handle heavier loads than thicker films.

Is your stated .0025 clearance cold? What does that become when the engine is at operating temps?

Our engines do not leak oil from the bearings any more than other engines of that period. This is not an issue of synthetic oil or reduced oil pressure either. I'm using 30-35 psi for normal at speed oil pressure. I use the smallest oil pumps with two cover gaskets to insure the pump does not get into the pressure relief valve when hot. No wasted pump energy. The oil pressure trace looks just like the RPM trace. You do have to be careful during hot idle situations. The driver is busy until he shuts the engine off in his pit.

There is no flooding to maintain film strength. You maintain your oil pressure, you have no bearing failures.

Brian

[brian]

You know Brian, Ive never been able to mike a hot engine. Honestly, I don't know what the clearances are hot. A common failure in vw's is a frozen rear main. The quickest way I know of locking up a rear bearing is to have an oval bore in the case. A .001 out of round rear main bore is a 40% reduction in clearance. Another issues in insufficient end play. While I have never been able to measure it, at high rpm, the crank is flexing in the middle and moving back and forth. On virtually every motor i have taken apart has had some contact in the center main. I have seen high speed films from a spintron test on small block chevys and the cranks are really moving around there.

[hardingfv32-1]

The load a bearing can support increases to infinity as the oil film thickness decreases. Smaller clearances would reduce crankshaft flexing in that case.

What would cause the crankshaft to move fore and aft? It is under load from the camshaft drive gears.

Brian

[brian]

Our beveled cam gear is one and thrusting from the clutch assy is another.