JD G piston/liner clearance question ???

Crazy Horse

Well-known Member
OK, I"ve been given and have read more than one answer to this question so I"ll try the JD guys at the YT forum to see what they have to say.

For a John Deere model G having cylinders bored to 0.045" oversize ..... the replacement pistons are alumninum. What is the recommended piston skirt clearance ???

Thanks for the replies !!
 
What do the pistons measure? The block should be bored .045 over standard and the clearance is in the pistons. I am just guessing .010 to.020 clearance on that size. It has been over 40 years since I bored & fitted them.
 
Teddy has is right. The machine shop bores the cylinder to the .045 over but when they did mine I asked them to take out another .002 in my bores the last time I had a G block done. My G pistons (.125 over aluminums) had .013 clearance.
 
Wow. 8 is way too tight. I don't think I'd want cast iron pistons that tight in a big bore like that. I just built a B with 5.06" billet aluminum pistons & the maker demanded 0.024" minimum. It's at 0.026" & works excellent. Add another 1.11" to those & you'll want even more. I would guess .025" minimum, prolly close to 30.
 
(quoted from post at 13:52:14 06/23/14) For a John Deere model G having cylinders bored to 0.045" oversize ..... the replacement pistons are alumninum.

Traditionally, the cylinders get bored to match the pistons. Generally the piston manufacturer would have a very good idea of the required clearances.

Assuming that they are long gone or unknown, a common safe rule of thumb is something along the lines of .0015" per inch of bore assuming you have new round (as opposed to cam ground) aluminum pistons. So at a nominal 6.125 you're at about .009 clearance.
 

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