Hi,
Im up to assembling a Chevy 355 engine. I just wanted to check a few things with you guys before proceeding...

The pistons (speed pro hypers, H631CP30) are very tight in the bores! I know that these pistons wants minimal clearance but Im worried that it will be TOO tight when the engine reach working temp. The pistons have a snug fit even without the rings, you almost have to "push" them trough the bores! .002" wont slide in between piston skirt and bore.

Anyone, Should they be this close??

You need to get someone to measure the bore IDs. It's possible they weren't correctly honed to finish size.

What does the mfg call for? Hypers and cast pistons don't need a lot of clearance. Also, cold pistons are not perfectly round. The mfg should spec where to measure them.

The teflon coating on those pistons makes a difference. I wonder if yur machinist honed it according to the diameter of the piston at the bottom of the skirt where there is no coating.

TP,
DO you have the box that the pistons came in ? On the side of the box there will be a minimum bore size that the block needs to be. On the coated pistons, you CANNOT measure the skirts to get a clearance size. You have to go by the size printed on the box as a minimum. We generally finish the bores about 1/2 thousanth (.0005") bigger than the minimum size because we know most engines with those pistons are going to be thrashed some.
Bottom line is .. you have to measure the bore size !!

PS, they sound tight to me, I have used quite a few of those pistons and never have had to use any real pressure to get them in the bore.

Yea and forged pistons expand more than cast or hyper's so that could be a problem.

Thanks for all your help guys! Well, I will measure the as soon as I get back my micrometer so I can set my bore gauge. I check the bores with my bore gauge (without a outside micrometer) Ya know I cannot measure the bores this way, but I can compare them and check roundness etc etc. The block is honed with torqueplate and I measure without one so I know this will affect the readings. Anyway, some bores were about .001 out of round, I know this probably will change when torqing down the head bolts. But other than that they seem to measure very similar all 8 cyl. Now im just waiting for my micrometer to get real measurements. The reason that I ask was that Ive never used coated hypers before, and they seemed kinda sticky in the bores, maybe im just paranoid =)

Bill K,
Thanks for letting me know that speed pro are writing skirt size & minimum clearance on the box! Ive never thought of that and the letters were VERY small, but when you know that they should be there, you'll find them!
It says: skirt size 4.02875 +/- 0.00025 inches
Minimum clearance .0010

I really appreciate your help!