sabastian458

I'm wrapping up my 403 LS2 build and the last parties measuring piston/deck clearance for head gaskets. Using a 4.5 inch bridge with micrometer set to "0.000" off the deck, I found that my measurement has fluctuations. The top portion of the piston, where "quench" is at, the piston measures any where from .006-.007 above deck to as low as .015 below deck, when the piston is rocked in the bore.

I rotated the engine off TDC and measured the opposing bank and found the same situation. I know using forged Pistons required specific piston/bore clearance, in which I had the block bored/honed to (with torque plate) by my machine shop, but is this rock excessive? Or am I being paranoid over nothing and should use the above deck measurement for calculating proper "quench" for head gasket thickness?

93 lt1 vette

So your saying you're getting .022 of piston wobble in each hole? Did the machinist have the Pistons when he bored and honed the block. Piston to wall clearance sounds way excessive.

CaseyJones

Piston expansion may vary between piston composition and manufacturers. I'd check with the manufacturer and find the optimal clearances and tolerances. If you are outside that range then you have problems.

Rob 02

Forged pistons expand more with heat than cast OEM 1's, so take into account that they are cold. Can you consult the manufacturer for specs?

sabastian458

I will recheck wisco's piston/bore cleared clearance. Yes the machinist had the Pistons at time of bore/hone. I'd originally measured my bore and then ordered one size larger so it could be machined to spec.

93 lt1 vette

I agree with the above statement that Pistons will expand but .022. That would be like running STD Pistons in a .020 over block and end gapping the rings to seal the holes. Imagine the slop once the rings are fully seated.

sabastian458

I edited the first post with a video from my cell phone

LoneStarFRC

Check with the machine shop as well and see what the actually measured.
PW clearance s/b .004 (~)

sabastian458

Wiseco' piston bore clearance recommendation is .001 to .003" clearance

LoneStarFRC

Also depends on the specific application, hence the (~) in my post which btw, I corrected to reflect what I meant to post, which was .004.

sabastian458

I thought you may have ment .00x instead of .000x. I sometimes still do the same thing when dealing with them, one reason I've learned to measure 3-4 times before going to my next step.