911 deck height after heads were flycut .012"

chtom1981911sc · 10-08-2013, 04:17 PM

After replacing broken lower headstuds ,I had the heads machined to clean up the damage from running it with broken studs. The machine shop flycut the heads .012". After assembling the motor and checking the deckheight I found it to be 1.02mm using the solder method contained in Wayne's book. I'm working on a 1981 911sc 3.0 with Mahle pistons & cylinders. I installed the .25mm copper cylinder gaskets to acheive this measurement. I this too tight? The book says 1.25-1.5mm desired clearance. Also did the machining change the CR too much to run pump gas? Already using premium fuel in this car.

Steve@Rennsport · 10-08-2013, 06:07 PM

1.02mm is just fine,....too much deck height contributes to detonation.

Just don't run too much ignition timing and you will be OK.

fred cook · fred cook's Garage

What Steve said! The original compression on your engine was probably 9.3:1 so that small head cut should not bump it too much. Actually, machining the heads did not affect the deck height. That is determined by the relationship of the cylinder height, rod length and piston design. I'm running a deck height of 1.1mm in my 3.3SS with a compression ratio of 10.1:1 and it runs fine on 91 octane pump gas.

Eagledriver · 10-09-2013, 01:47 PM

Quote:

Originally Posted by chtom1981911sc

After replacing broken lower headstuds ,I had the heads machined to clean up the damage from running it with broken studs. The machine shop flycut the heads .012". After assembling the motor and checking the deckheight I found it to be 1.02mm using the solder method contained in Wayne's book. I'm working on a 1981 911sc 3.0 with Mahle pistons & cylinders. I installed the .25mm copper cylinder gaskets to acheive this measurement. I this too tight? The book says 1.25-1.5mm desired clearance. Also did the machining change the CR too much to run pump gas? Already using premium fuel in this car.

The measurement you did is not a deck height measurement. It is a piston to cylinder head clearance measurement. That being said, it indicates you won't have a problem with interference on the cylinder head. I would also say you should have no problem with compression since you have a lower compression USA engine.

-Andy