another deck height question
 

this is on my stock USA 78' 911sc

Im doing a test fit on my new JE pistons after having my heads redone. I had one cylinder with some damage because of a blown ring gasket, combined with some broken head studs, which looked just like the pictures in Waynes book. I had 3 of the cylinders machined the same with the idea that the bank would be matched. I ordered six 0.50mm cylinder base gaskets along with another six 0.25mm cylinder base gaskets.

Here is the puzzling part... i assembled the passenger side (4-5-6) with the 0.50mm base gaskets, which were the cylinders that had the machining done to them. EBS recommends that the JE pistons have a 1mm distance from the top of the cylinder. I measured between .046 and .052 inches with my gauge for all cylinders at the wrist pins. This translates to about 1.2 mm on that bank.

Now, on the bank where the cylinder tops were not machined, I expected that the 0.50mm base gaskets would give a deck height greater than the machined cylinders. On this bank, with the .50mm gaskets I measured .048" on #1 and .038" on #2 and .039" on #3. I had to add the .25mm gaskets to #2 and #3 to get heights of right at .049 inches on #2&3.

Is this a normal variance or should I be concerned? Im thinking as long as I have at least 1mm (.040") I should be ok...right?

ok...after further reading, I think the purpose of getting the deck height set right is really to insure that the heads & cam towers bolt to a level surface. JE recomends 1mm but Waynes book recommends nothing less than 1.3mm. I have also measured the cylinders from the base to top and noticed some variance between cylinders there as well. Anyone else gone thru this?

looks like im answering some of my own questions. It seems that my cylinders are not all the same height either. not off by too much but off by enough that I can mix them around with other case holes to measure deck height. So here is where im at on deck height

#1 1.28mm with .25 & .50mm cylinder gaskets
#2 1.33mm with .25 & .50mm cylinder gaskets
#3 1.36mm with .25 & .50mm cylinder gaskets
#4 1.23mm with .50mm cylinder gasket
#5 1.23mm with .50mm cylinder gasket
#6 1.17mm with .50mm cylinder gasket

again, wayne recommends at least 1.3mm and JE recommends 1.0mm, so im somewhere in the middle.

Hey!

I see you're still having fun with this! ;)

Wayne's recommendation should only apply to factory Mahle or KS pistons as that is the deck clearance they were built for. JE's are designed for 1.0mm. I have had JE make pistons designed for greater clearance because of customer requests but they are otherwise designed for 1.0mm. At that height they should offer plenty of clearance around the dome and should provide the advertised compression ratio.

Don

Thanks Don... In case you havent figured it out, im the guy that called you twice last week all worried about deck heights! Im now fighting the circlips! There has got to be a tool or something to get those clips in there. Im all bloody :)

Yeah, those clips can be bastards! However, Stomski makes a circlip "injector" that we keep in stock now. Let me know if you need one!

Merry Christmas!

Don

A thank you to Don and anyone else I pestered at EBS! the engine is all back together and feels great. I have about 100 miles on the car and my fear of it falling apart is diminishing ;)

Don and his team at EBS are great to work with, THANKS AGAIN.

Steve