CP piston install question?
 

Ok I bought a set of CP pistons a few years ago and I’m now assembling the engine I got them for. Problem being they are L and R short skirt pistons but with double valve relief. So when I look at pistons from bottom you can see one corner is thicker than the others. I’m assuming the thicker area would be under exhaust valve or am I totally wrong?

It is my understanding from talking to Barry Calvert (President of CP) and his brother "Snake" at the PRI shows that CP Pistons were "Non-Directional" meaning the piston does not care which set of valve reliefs you install upward.

No direction arrow on which way should face the front of the engine. But that was some years ago, just like the age of your pistons.

Tom V. .

Can you see in the picture where the one corner is thicker than the others?

I would guess the thicker corner would be positioned to the trust side. Unless it is just because the pin is offset, could position it either way depending on the use.

Non-directional means no offset like a factory piston. See post #2.

If you have a non directional piston then both sides of the piston can be the same contour/thickness and no reason to add more weight to on side of a piston to make it thicker and "stronger" on the thrust side.

Tom V.

The shorter thick skirt is hard to see in the picture. Pin offset I thought I noticed was likely and optical illusion.

Main point I was trying to make was is if one side of the skirt looks like it has more support or skirt area, it was likely designed to be positioned so that the larger skirt area was to be positioned to the major thrust side of the cylinder. If the thicker looking side is thicker looking because they machined it shorter and the piston is symmetrical like Tom said, then it probably belongs on the minor thrust sided. Doesn’t sound to me like the pistons are non directional if the skirts are not identical. Fwiw

The top down shot of those pistons ( if taken close to being centered) really looks to me like the pistons have valve notches for both early and late heads due to the notch off set.

You set them up on the rods for the heads you are running (since there’s no Wrist pin off set )that being 20 or 14 degree, very efficient and clever by CP!

Agree. Very clever.

Tom V.

If the OP is talking about the under side of the valve relief, then I would think the thicker area would be for the intake valve. Manufacturer leaving more material for the intake valve relief due to the valve being larger and the relief for the intake valve usually being a deeper cut in thw piston.

Yes it is the underside that is thicker the skirts are the same on each piston that’s what I didn’t understand because they are R and L pistons for each bank. That made think if the thick area was for heat distribution from exhaust side.One thing I learned on this build is don’t build a shortblock around used pistons. LAL thanks for the replies

If the Op will confirm that the valve notches are cut for both early and late valve inclination heads then whatever difference there happens to be in thickness of that corner material is a 100% moot point!

Valve notches look to be the same both sides all are .168-.170 deep. the thick area I’m talking about is mirrored from the L to R pistons. See picture.

The other picture was an optical illusion, No 389/421 valve reliefs on those CP pistons.

Thanks for the better pictures.

Tom V.

Yup, far different then in that first photo!

I talked to a CP tech today and you are correct this piston can be mounted either way. They said don’t worry about the thick area. Thanks for the replies

GLAD IT STILL APPLIES TODAY WITH THEIR STUFF.

I talked to Barry & Snake at every PRI show held in Florida back in the days when Bob, Frank, I, the Butlers, and the guy who used to make the cast iron round port manifolds worked that show every year. Promoting Pontiac HP New Parts.

Tom V.

Anyone have a good guess of the cc on the pistons?? I’m thinking 16cc I never did check.

Looks like a TRW stock replacement valve relief which would be about 6.7 cc.