72 combat ring gap clearence.

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stevesbsa

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Dec 18, 2010
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checked bore, and measured standard bore, honed and remeasured to 2.8755. Order standard pistons and hasting rings. Pistons measured around the same as the old ones, 2.890. The problem was the ring gap measures .020 the manual says .008 to .012. .020 is the same gap I had on the old rings. Nothing has really changed from the old to the new parts. I measured the cylinder with a bore gauge and the machinist checked it and found the same with a .002 out of round. Why is the ring gap off from the Norton manual. I bought .020 oversize pistons and rings, I don't want to end up with the same scenario.
 
stevesbsa said:
checked bore, and measured standard bore, honed and remeasured to 2.8755. Order standard pistons and hasting rings. Pistons measured around the same as the old ones, 2.890. The problem was the ring gap measures .020 the manual says .008 to .012. .020 is the same gap I had on the old rings. Nothing has really changed from the old to the new parts. I measured the cylinder with a bore gauge and the machinist checked it and found the same with a .002 out of round. Why is the ring gap off from the Norton manual. I bought .020 oversize pistons and rings, I don't want to end up with the same scenario.
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I have run into the same problem with new rings but they were GPM rings and pistons from Italy. Must be that these manufacturers are making new rings that are a bit too large or that they are playing it safe avoiding seize-ups and assuming nobody knows how to gap them properly! 0.020 isn't that far off and may last you a lifetime depending on how you ride the bike. Better to have more gap than less and you are probably good until 0.028 or so. The gaps in my GPM rings for my Dominator were about 0.020 and I too was wondering why they were so large. I just installed 'em and ran 'em and they seem fine.
 
stevesbsa said:
checked bore, and measured standard bore, honed and remeasured to 2.8755. Order standard pistons and hasting rings. Pistons measured around the same as the old ones, 2.890. quote]'

How do 2.890 pistons fit in a 2.8755 bore?
Click to expand...
 
stevesbsa said:
checked bore, and measured standard bore, honed and remeasured to 2.8755. Order standard pistons and hasting rings. Pistons measured around the same as the old ones, 2.890. quote]'

How do 2.890 pistons fit in a 2.8755 bore?

Yeah good question ! Forgot the 6 2.689
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