Piston to Valve Clearance

[126coupe]

I am performing my clearance's for my 2.0L 10.5:1 race engine. I am performing this measurement because I went from a DC60 Cam to a DC80 Cam.

In 2 spots I only have .5mm of clearance on the intake and 1mm of clearance on the exaust.

I am performing this measurement with no head gaskets.
Would performing this measurement with the gaskets make a difference?

Should I have 1mm of material removed from the valve pockets? I would like to have as much CR as possible.

These are J & E pistons.

Your thoughts

[Eagledriver]

Yes.

1mm is good enough according to the early factory workshop manual but .5mm is not. Since you are going to have to machine the pistons I'd shoot for 1.5mm as recommended by several engine builders on this forum. The gaskets will not make a difference (assuming you are refering to CE rings).

-Andy

[304065]

Mark, of course you are talking about the 80mm head gaskets, not the 84mm and later CE rings, but I have never read that they make any difference in the piston-to-cylinder clearance: the seal is between the top of the cylinder and the head surface, with the gasket around that.

I'll let the guys with experience answer the part about the clearance.

[126coupe]

Originally posted by john_cramer
Mark, of course you are talking about the 80mm head gaskets, not the 84mm and later CE rings, but I have never read that they make any difference in the piston-to-cylinder clearance: the seal is between the top of the cylinder and the head surface, with the gasket around that.

I'll let the guys with experience answer the part about the clearance.

I use the 80mm head gaskets. I just got off the phone w Ollies. It looks like I need to remove 1mm from the intake pocket and 1mm from the exaust pocket. this will get my clearances to 1.5mm and 2.0mm. I will lose a little CR, but thats better than hearing the dreaded "clang"

[William Miller]

I had a simular clearance issue when rebuilding a stock 3.0.
I retarded the cam timing to euro spec and it solved the clearance issue.

My question is this: On an earlier rebuild on this same engine, It looked like the valve seats were replaced. When closed, the valves face protruded a bit into the cylinder about 1 or more mm. During my project, I had the machine shop replace the seats and I supplied new valves. The machine shop cut the seats so that the valve faces were very close to flush with the head instead of protruding.
It seems like my shop did it correctly, but I don't thing I've seen any specifications on this.

I had to rebuild the engine because of a broken ring. When I took it apart, I found marks on two pistons where the intake valves made their mark. One of the two had the snapped ring. It was not a catostrophic failure, but looks like it was due to slight mechanical contact over a period of time.

So I was wondering if grinding the valve seats would give you the same clearance as making the pockets in the pistons?

Seems like less disassembly.

[Eagledriver]

I failed to notice the engine size on my comments. You got the right answers though.

I think it will be cheaper to pocket the pistons more than having the valve seats redone. Also don't think you can recess them that much.

-Andy