What does "bored 10 over" mean?

[trad1987]

I need to replace my rings on my black top, but am not sure about the correct size. The previous owner listed that the motor was "bored 10 over" when it was rebuilt. Does that mean that each cylinder is 1mm larger in diameter than stock? Thanks for the newbie help

[UNITEDMASTER]

That means the cylinder has been enlarged by 10 thousands of an inch

[landins13]

yup what he said, when a machine shop refers to bearing and what not theyll tell you that you need 10 over stock, 20 over, blah blah blah, its reffering to thousanths of inches more than what stock is.

[VQMaxFan]

.010 of an inch

[trad1987]

do any of you guys know who makes rings that are only .010" over? Can't seem to find any

[VQMaxFan]

Get some 86.2mm piston rings.

[UNITEDMASTER]

When the block has been cut you need to change the pistons & the rings. Off the top of my head I think nissan has OEM replacements that are 10 over. Did you take your motor to a mainly domestic machine shop. Why did the block need to overbored? unless the walls were damaged ,a clean up hone should have done the trick. By changing only the rings you may or may not encounter piston slap. Check your bore clearance VS whatever piston you have ,if its out of spec, it doesnt matter what ring you use, its not legit. Generally a forged piston will run a slightly looser bore clearance

[trad1987]

I'm confused here. So 10 thousandths = .01" .01"= .025 cm. .025cm = .25 mm. Therefore, the bore is 86.25mm correct? Is all my math correct here?

[UNITEDMASTER]

Well yea thats a problem your trying to put a biger ring in a smaller hole & that creates other problems(excess friction on the walls, incorrect ring gap,possible ring butting. To me , if this is the way it was setup before thats why the motor is wearing out rings. From what I know a bad tune will break rings, or gas wash the cyl & that leads to excess wear. Tell me what parts you have!!