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Dumb question time . . . . Brand new stock jug 89.0 bore, brand new stock cast piston, brand new standard rings . . . . wash the Honda honey off the bore, slip the rings in with the slug so they sit square, end gaps measure 19 and 20 thou. . . . . is this about right ? I know there was a formula that stipulated the end gap as a percentage of bore circumference, but I'm buggered if I can find it ! Just want to make sure this engine is as safe as possible. Any opinions ?

I'd have looked for .018", go with the .019"

have you measured that cylinder to see that its skirt is proper size?

ring end gaps measure the same top and bottom, so yeah, it seems pretty parallel. exhaust bridge is relieved too, so it seems ok to bolt up ?

This is one thing that piss' me off sometimes.

The end gap in the manuel says .018-.020 max. I think there is a minium of .014?

I have yet to see an end gap of less than .018 with a fresh bore and rings.

other wrote:Dumb question time . . . . Brand new stock jug 89.0 bore, brand new stock cast piston, brand new standard rings . . . . wash the Honda honey off the bore, slip the rings in with the slug so they sit square, end gaps measure 19 and 20 thou. . . . . is this about right ? I know there was a formula that stipulated the end gap as a percentage of bore circumference, but I'm buggered if I can find it ! Just want to make sure this engine is as safe as possible. Any opinions ?

I know the formula for a forged piston is usually .004" for every inch of bore.. for cast i'd just use the same... can't hurt... i've took a kx125 engine apart for a customer that had a ring end gap of .020" and it ran fine.. lol thats no joke.

If the rings ever butt, its all over. Go with ther bigger gap.

Roosty measured my end gap last summer at his shop when we were changing a couple of gears out in the trans. .050. That's right. 50 thou. Slammed it back together in June and rode it out to the end of the season. Fuck it, it's a Honda. It's bulletproof. Lol

Agreed Scooter (and Bob ). Gap can be big, no drama, they just blow-by a bit. Gap's too small, they blow-UP a bit. That's was the one I was tryin' to avoid !