924Board.org

[kaffine]

Well my 931 wont stop burning oil so I'm going to rebuild the engine. Are there any pistons that will make it a non interfence engine? I don't like interfence engines with timing belts or chains.

Those of you using the VW pistons how are they holding up?

Thanks.
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80 924
80 931

The best desciption of an atom boils down to something unknown is doing we don't know what.
Sir Arthur Eddington

[Smoothie]

Forged flat tops - jl924t did it. Look here - http://www.924board.org/viewtopic.php?t=9809
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[endwrench]

From what I understand the VW piston is a flat top and sits 5.4mm down the bore. This equals .212". I just measured a used 924 (not 931) head gasket and it is .068". A quick measurement of the 931 combustion chamber depth to the valve face gave .190".

So .212 + .190 + .068 = .470". The exact valve lift of a stock 931 cam! Creepy! I would think you could mill a couple shallow pockets around .020" in the piston tops for a margin of error. Being this close though, the only way you would know for sure would be to assemble and check it.

You could also use an early model 924 cam with .412" lift or use a regrind like mine with .435" lift. My cam may be better than I first thought. It seems to be performing well with the EFI setup and supercharger.

Todd

[Raceboy]

I checked mine with 2mm Copper head gasket, nothing to worry about: I turned crank without having timing belt and everything checked out fine.
But: a) I haven't torqued the head to the specs and b) with stock head gasket it sure will be VERY close.
I would go for the small valve relieves, just for piece of mind
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[endwrench]

Hey Raceboy, good news! If possible, would you mind doing a "clay" test with the piston at TDC then turn the cam one full revolution? Are you using a stock cam?

Todd