No bore gage - no problem!

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Tractors Owned: Restored: 1950 Cub, 1950 Cub Demo, 1948 super AI, 1935 Silver King, 1946 Oliver 60 RC, John Deere M, 1950 C demo.

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No bore gage - no problem!

Postby artc » Sat Sep 27, 2008 5:49 pm

i got to thinking about another thread where the initiater of the thread was trying to determine the condition of his engine after dissassembly. i would simply reach for the bore gage, set it up, and measure away. but its a tool most do not have, simply because its a one use tool for many.

one of the things you should always do with new rings is test fit them in the bore and measure the end gap for tolerance and that the rings are correct for the block. just because it says STD or .020 on the package doesn't mean anything.


try this. your engine is dissassembled at this point anyway. what you are trying to determine is 'to bore, or not to bore'

remove a top ring from any piston, and insert it in the empty bore of the cylinder as if it was on the piston. position it using the piston to push it down 3/8 to 1/2 inch. (you use the piston to get the ring square in the cylinder.)

use a feeler gage (or 3 or 4 together) to get a ring end gap. then use the piston to send the ring to 1" from the bottom of the cylinder. theres no wear down there because the rings don't make it that far. measure ring end gap again. It should be less.

subtract the two numbers and divide by 3.14. that number is the wear of the cylinder at the worst point typically.

for instance. Kit's motor is in my shop now with badly worn rings and a block worn to max. or close to. at the top i have .100 end gap. at the bottom, .082. .018/3.14=.006. it means that i have .006 wear in the cylinder - tolerable for a motor that's not going to work 10 hours a day.

When the engine was new, the rings were probably in the .010 gap range in a new bore, so this motor has worn over .024 off the diameter of the rings. thats a lot! It still ran, BTW

maybe this helps someone.
'If they're tappin', they're not burnin'

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