Its actually on my 408 stroker windsor Ford... I am putting my short block together. Its a .40 over 351w and I have forged SRP pistons. I took my block and rotating assembly machine shop, they went through and balanced the rotating assembly and said that my rods and pistons weighed perfectly the same and I could put any piston in any hole becaues the bores and piston diameters are perfect. So I get everything back home and just tinkering around I put a piston in a hole and noticed it has a little side to side movement (rocking piston towards front and rear of block) but when I try to rock it up and down (towards oil pan and intake) it is nearly flush and no movement. But since the piston cant move side to side when its running because of the rod and rod pins position is this still something to worry about? Is that how SRP designed the pistons in the first place?

Thanks for any input!
-wes

That is because the pistons are not round.
Also there is no skirt to hold the piston in that direction.
No Worries :)

Pistons, ESPECIALLY forged ones, change size and shape when they get hot. They're designed accordingly. Forged ones pretty much always fit loose in the bores when cold, which is why people say they're "noisy".... they have good reason for saying that. The noise goes away when they get hot.

If your machine shop guy signed off on the bore clearance, then most likely it's OK.

Are you sure you don't have the direction it rocks backward? It should be able to rock side to side (toward the intake and pan) and not front to back. The wrist pin should not allow it to rock much if any front to back. At least that is what makes sense to me. Now if the piston has no rings on it yet, it may slide front to back slightly, but should not be able to rock in the bore front to back. It should however, rock a little side to side from intake to pan. Unless they were hypers, and they have to be so tight it seems like they barely fit in the bore!

I have built a bunch of motors over the years and have come to expect piston slap from the forged pistons, if you have a quiet exhaust and valvetrain you can expect to hear it until the motor is warmed up. The newly rebuilt motor seems to do it more because the break in needs to take place. The shorter the skirts the more likely the noise will be noticable, you should see the Buick 455 piston. It resembles a diesel piston with a full skirt, it is made that way for better stability and less noise but doesn't do any favors for making HP. I put wiseco light weight pistons in mine and it makes a bunch of noise at start up because they have just the two sides with skirts along with being a huge bore size.

Nothing to worry about on yours, it will go away after warm up. :yes:

Steve

If the pins are offset, say, .060", then turn them around and install the right bank of pistons in the left bank and visa versa to create a better, although more cold slap, running engine b/c the pins will get just a schosh better push on the crank rod journals due to a very slightly better angularity deal!!

My old junk301 was put together this way.

pdq67

wes,
Want to try something interesting ..... put the piston in a pot of boiling water for a couple of minutes. The pick it up with some gloves and try to put it in the bore. Let us know what you see.

Thanks for all of the help! :beers: