Has anyone been succesful at running their piston to head clearance at .026" on stock internals? Engine is a F20b. Had the head decked .020" and when I got it back it looks like there is some core shift, and #1 and #4 combustion chambers around the outside are flush with the head surface. When I initially measured it in the quenches, .020" was supposed to leave me .004" in the quenches, but it looks like it didn't in those outside combustion chambers. So I guess I'm looking at .026" piston to head clearance. Anybody run it this tight with problems?

 

IMO .026 would be touch and go with used stock internals on a F20B. I have been doing research where .030-.026 is a quench clearance that a lot of builders run. However that is with new internals that are tested. Even with new parts you need to know how much they may stretch @ a given temp and RPM in order to determine reliable clearances.

Another question is. What are your piston to deck and piston to valve clearances? Is your piston to deck 000 or is it out of the hole like the rest of the F series blocks -0.02. Not a lot but it still tightens up that clearance a little bit more. Don't forget that you are also closing the gap on your piston to valve as well. You may want to go with a .03 crush height head gasket.

Clay the engine to be sure what your clearances are.

 

piston to deck was measured rocking the piston fore and aft. averaged out to flush with the deck. Dynamically, it's hard to guess what the piston to deck will be, so I was wanting a little more clearance. But it looks like I'm gonna be stuck with the gasket alone for clearance. I haven't looked much for aftermarket headgaskets for the f20b, but maybe I'll have to come up with something. Nobody has ran piston to head clearance at .026" successfully?

 

I ran a .015" on a forged B16A

It made me go nuts, I was scared to rev the motor, to beat on it, etc...


I would go to the safe side if I were you and run a thicker gasket..

 

damn, .015" piston to head? yeah, I don't think that would work for this stock engine. How long did you run that engine? What did you rev it at?

 

I don't remember the clearance off hand, but I've worked on an engine where the pistons would kiss the head when it was cold. Once the block warmed up it would get quiet. It revved to 7000 a lot (race track) and was replaced with a newer engine after 60k miles of track and city abuse. On teardown we could see where the carbon was kept off of the quench areas. I'm not suggesting you do this, but I think 0.026" would be fine.

 

but you don't remember if it was tighter than .026" I know there are alot more variables, and human error when measuring. But everybody says .030" is safe. But everybody's technique when measuring piston to deck can present different variables also. I'm a little leary about .026" on stock rods, but if it was a race car, I wouldn't be against running it and seeing what happens. But this is just my street car, so I don't have that luxury of "finding out". lol. I was just seeing if some people have done it at .026" or tighter and not had "contact".

 

It was quite a bit less than a HG thickness; I'd guess a bit over 0.010". It was a hybrid build with pistons sticking out of the deck. If you think about it the GSR engines have quench areas flush with the cylinder head, and iirc the edges of the pistons are about flush with the deck, so the thickness of a HG is all that separates the pistons from the head.

 

What head gasket are you thinking of running to get your 0.026" clearance. If OEM 3layer then your pistons are out of the hole which would be okay for a PR3 Head but not a GSR head (B-Series analogy).

I'd spot face the head to get back your clearance.