1980 911 3.0 SC deckheight
 

Hello,

I have a 911 sc from 1980 with KS piston and cylinders and are rebuilding the engine. Not the entire engine because it was running ok. The reason for the rebuild was broken head studs. The part i did not do in the rebuild was split the case, so the last part i took of ware the pistons.

Now i am starting the rebuild and have put the pistons (with new rings) and cylinders on the blok. When i check the deck height i measure the following:

cylinder 1: 0,95 mm
cylinder 2: 1,20 mm
cylinder 3: 1,10 mm
cylinder 4: 1,14 mm
cylinder 5: 0,96 mm
cylinder 6: 1,02 mm

My question now is:

I did not do anything to the long blok itself, how can it be that for 2 cylinders the measurement is under 1 mm ?
And do i realy need to put extra gaskets in for these cylinders. (all cylinders had one gasket installed and ware put back with 1 new gaskets for each cylinder).

Thanks for responding,

I wouldn't worry about the .95mm measurement. That's close enough to 1mm to be safe. I'd worry about the differences though. Are you sure the cylinders are seated fully in the case? Did you use a hardening sealant on the base gaskets?

You may have trouble with the cams binding when you put the engine together if the cylinders are different heights. You might want to do a trial assembly of the top end to check for camshaft binding before putting on the sealant and doing the final assembly. Don't put the CE rings on during the trial assembly.

-Andy

Thanks for your answer Andy,

I have the cylinders mounted and secured only hand tight with one bold and a round 19 mm copper pipe as a spacer to replace the head. I also did not use any sealant jet, because i was unsure about the measurement.

I am following the book how to rebuild and modify Porsche 911 engines by the letter and have not much experience with the exact engineering behind the engine, so i can not interpret certain parts due to lack of knowledge. But there we have the Internet for.

I will secure all the head studs with spacer and take all the measurements again.

Benno.

If you use a sealant, use a non hardening kind. I use a permatex material that doesn't harden. Curil T would work here as well. Do not use a hardening sealant like the Locktite 574 on the cylinder bases. What will happen is the sealant will dry and space the cylinder out from the case before you can put the heads on tight.

-Andy

Thanks for the info, i was gone use curil-T so it should al go well.

I would check again. I assume you are using a caliper to measure the deck height. Brings a few variables into play. Fasten the cylinder in opposite corners (at least two nuts on it) to hold it square. You can probably rock the piston a wee bit in the bore when it is at tdc and that can also affect the measurement. If the caliper is not perfectly perpindicular that will also bring variables in.

Cheers