does this seem normal. im building a 489 for my pachanga. started with a 330. now its going to be a forged 489 with 781 heads. anyhow. i bought some 14cc dome 2618 diamond pistons. they want the piston to bore clearance at .0055. with open cooling marine motors adding another.002-.004. this seems like alot to me but ive only ever built car motors. i understand the block staying cold and the piston material growing. but this motor will be lucky to make 475hp and will only be WOT for about 5 minutes total a weekend.

is .0055 ok or should i have the machinist open it up more. im dropping the pistons off this week for the final bore and i need to know what to tell him

thanks, Brandon.

You really should go with what Diamond tells you. They know how to make a piston and they also know what kind of material they used to make the piston and how much it will grow. If you gave them all the specs of the build and the intended use then go with what they tell you. If you have an old piston measure it with a set of calipers then throw it in the oven for 20 minutes on 400 and pull it out and measure it. I don't think you will be worried about the piston being loose anymore. My piston to wall (Diamond) n/a is .0065

thank you

On the flip side I know a few folks who put marine motors in their car and were freaked out with how loud they clamoured until things warmed up.

we run an xtra.001 if not running a thermostat or circulating pump.

Call diamond with the job number off your piston spec sheet. Discuss the build and intended use with them and they will be happy to confirm. I built 2 pro charged 383's using there pistons. Marine required .005, add .002 for open cooling add .002 for boost. Well that adds up to a sh!t ton for a 4.030 bore! I called talked to a tech and he said go .0065 -.007 so that's where we are.

Perfect solution. I'll never understand why people won't call *boutique* manufacturers. They're the ones that eat, sleep and breathe parts. Ones where you might get help from an engineer or designer.

gotta watch those engineer,s.lol.

Piston slap when its cold doesnt bother me. I called diamond and got some girl who said i would have to talk to the distributor i got them from. Ill try again tomorrow and be more persistent.

I got it taken care of thanks guys.