I bought a set of SRP pistons off the owner of a semi local shop. I was told the were 81mm's but they do not fit at all. I know forged pistons expand more than oems so they should be fairly easy to drop in without rings on them. I mic'd the skirts out and they came out to 81.5mm. The undersides of these pistons have a "20" stamp on them which im thinking means these are 81.5's sonsidering the 81.5s on the site signify .20 over.

Let me know if you want some more info. Oh yeah, i measured the oem's i pulled out and they are 81mm measured with the same mic

 

.020 is roughly .5mm

 

Just take the block to the machine shop to have them match the bores to the pistons and hone it for you.

 

Or save the money and get the pistons you were supposed to originally get. Why spend more money on machine work when he clearly stated he ordered 81's.

 

what is the part number on the buttom of piston

 

If they are marked 20 on the bottem theyre .20 over. Which is obviously 81.5mm. Get the right pistons.

 

He seemed like he thought i was stupid. I know the PTW clearance needs to be a good amount higher than oems due to expansion, so they should drop in fairly easily. Ill see what he wants to do about ot

 

id use those 81.5 if there good condition. fresh bore/hone will really help give the rings a better platform to seal up on. just my .02

 

There's been some fairly clear evidence that SRP's expand more than other pistons with high temps, so you'll really want to get the correct amount. I would *highly* recommend you have your block honed out to at least .0035" wider than those 81.5mm pistons, if not >.004". Not doing so (ie using 81mm) could lead to blowby issues if your bores aren't *perfect*, which is unlikely if it has more than 30k miles on it. Its very cheap to do, and one of the best things to do to prevent headaches that you can only solve by ripping the block apart after building it.

 

i agree

if you have 81.5 mm, i would bring the pistons and spec sheet with you to a machinest and have them do a bore/hone

this will provide a better circle/bore for the rings to seat with and will provide an overall more efficient motor

81mm rebuilds are ridiculous imo unless the block is brand new or your just doing a stock rebuild