piston to valve clearances - 2.7 CIS engine

[fanaudical]

I have assembled my 2.7L (CIS with CIS cams), being careful to increase base gasket thickness to compensate for the amount the case was decked and heads were shaved. I had what I thought was good deck height. After timing camshafts (and double-checking) I find that my intake and exhaust valve-to-piston clearances are a little on the small side. (I used the method prescribed in Wayne's book.)

I'm getting 1.25mm minimum on intake, 1.75mm minimum on exhaust. (Wayne's book indicates 1.50 minimum on intake, 2.00mm minimum on exhaust.)

I think I know the answer already (even thicker cylinder base shims), but what is the absolute minimum that is "safe" for a sedate street motor? (I have searched and see some conflicting info.)

Thanks for the help.

[Walt Fricke]

What did you do on the rebuild which could have changed what this engine ran just fine with before?

You've probably figured out that the normal drill is to replace with the shims whatever got shaved off the case spigot to get those all the same distance from the crank, and what you took off of the head mating surfaces. Otherwise you will get higher compression (which might work fine all by itself if not too much - the 3.0 Euros run 9.8/1 just fine) and have to deal with issues like this.

[Eagledriver]

I'd run with the clearance you have. Porsche shop manual says .8mm minimum.

-Andy

[fanaudical]

Thanks for the feedback.

Where does the Porsche shop manual for the 2.7 indicate 0.8mm min clearance? (I don't doubt it - I'd just like to find where I missed it in the copy I have.)

My case was decked 0.010" and the heads were machined 0.020" (~0.75mm combined). Original cylinder base gasket was 0.25mm. I installed 1.00mm base gasket and deck height was at the upper end of the limit (which, in retrospect, really doesn't compensate for shaved heads).