oversized pistons

[FullyBuiltDSM]

im about to rebuild my 92 gst and the pistons i purchased are .020 over. im kind of nervous about sending my block to have it bored. im not sure what the clearance between the piston and the cylinder wall is suppose to be. do i need to have it bored larger than .020 so the clearance is correct? or is the clearance already figured into the diameter of the pistons when there made? i know this is hard to understand but i dont know how else to explain it. i dont want to take it to a shop and say "hey bore this .020 over" and then have it too small or somthing. not many good shops around here so id rather explain it to them than have them try and figure it out

 

[SolidBoostTSi]

you should be alright, The factory service manual specifies .039 as the limit of over sizing pistons. I don't see why you are unsure unless your block has been bored out already to .0XX and you want to go .020 over and it will end up being .0XX + .020 = disaster just measure you bore first with a telescoping guage and refer to a service manual Haynes, Mitsu, Chiltons . hope that helps.


Solid

 

[99gst_racer]

im about to rebuild my 92 gst and the pistons i purchased are .020 over. im kind of nervous about sending my block to have it bored. im not sure what the clearance between the piston and the cylinder wall is suppose to be. do i need to have it bored larger than .020 so the clearance is correct? or is the clearance already figured into the diameter of the pistons when there made? i know this is hard to understand but i dont know how else to explain it. i dont want to take it to a shop and say "hey bore this .020 over" and then have it too small or somthing. not many good shops around here so id rather explain it to them than have them try and figure it out

Don't worry, you're machine should know what to do. .020 over refers to an oversize of the original bore. The original bore is 85mm (3.346") and your machinist should know to make that bore .020 over than that (which will be 85.5mm or 3.366"). If they know what the stock bore is and what your piston's oversize is, then that's all they should need to know to get the job done correctly.

This is all assuming that you want to have a factory spec wall clearance. Some pistons require a tighter or looser clearance which would be printed on a spec sheet included with the pistons. You might want to take a look at that or at least give it to your machinist.

 

[dr1665]

If they know what the stock bore is and what your piston's oversize is, then that's all they should need to know to get the job done correctly.

Not to mention you should take them your pistons and the spec sheet when you drop off the block for machining. They will be able to bore the cylinder to the pistons' specs so the clearances are ideal.

 

[gurmanator]

Not to mention you should take them your pistons and the spec sheet when you drop off the block for machining. They will be able to bore the cylinder to the pistons' specs so the clearances are ideal.

yes what you said .....have the pistons in your hot little hands and take the pistons and block together...no pistons are the same its all numbers.piston /cylinder wall clearance is .004 before you have to bore otherwise you run the risk of"piston slap".