i have a ls block with stock bore which is supposed to be 81mm but when i mic'd it it came out to be 80.86mm then i took another ls block that i bought that was supposed to be 82mm bore n mic'd it, that came out to be 81.43. i need to buy pistons for the "82mm" block but now im unsure as to what size pistons to buy. even if i was to buy 81.5mm pistons they wouldnt fit into the 81.43 cylinder, right??? im confused by these readings...its a brand new digital mic zero'd it in before i started and everything. am i just supposed to round it off to 81.5?? anyone's input would be very helpful! i need these pistons to put the motor together n dont want to order the wrong size!!!

 

if the block is 81.43, get some 81.5mm pistons and have it bored out to the right ptw clearance.

 

hate to tell you but your using the wrong tool.....you need a cylinder bore gauge AND a outside micrometer....also, you get what you pay for when buying precision measuring tools.......start searching ebay for a central tools bore gauge, I saw one of the sled types go for 15$ last week. If I hadnt just bought a periscope type gauge I would have been all over that....Its not the best brand out there but it will work for you. Central also has a cheaper brand called "storm" that can also save you a few bucks

 

but is it the gauge thats wrong? like i said the oem block should have been 81mm correct? it was 80.86mm is this supposed to be rounded up to 81mm? if so then i should round the other block up to 81.5 right?

 

bump for help

 

if you had 81mm piston in it already.. and you mic'd your bore and got something smaller don't you think your mic'ing it wrong or your tool is incorrect... i don't think you can put 81mm piston into a hole that is smaller then the piston.

 

Have you ever checked cylinder bore diamtere before? You might just be doing it wrong. When i did it the first time, my measurements were way off.

That or maybe your tool is not calibrated correctly.

 

THe GIGO factor is in play here. GarbageInGarbageOut. Swing your block by your machinist and let him/her tell you.

 

doing it according to haynes manual... thats why i was asking if the measurements were literal or if they rounded up...they were oem pistons supposed to be 81mm but they didnt mic up to be 81mm either they were like 80.6 or something dont remember exactly thought maybe the rings made up for the difference on the pistons

 

lets just round up every measurement and see what we get