rear cylinder broken piston ring

[cantho870]

I have a 95 evo with edelbrock performer heads .005 over  je pistons. was blowing smoke from rear cylinder. tore down and found broken top ring. Any reasons for this.what would be the best replacement rings. Pistons look good. Can i reuse them in new jugs. Approx 10-15000  miles on pistons.

[Trip]

I would ,very carefully, inspect the piston ring lands on the both..if in fact they,re in spec..you could order a set of Hastings rings and go from there...at 15....you "should " be able to just do a cleanup hone on the barells....i,d spend a lot of time finding out why a compression ring broke tho.....

[Tattoo]

 I agree something happened for sure.
where did it break?

[cantho870]

I agree something happened for sure.
where did it break?
[/ Top ring came out in approx 5 piecesquote]

[Mule]

 A broken ring could be caused by not enough ring end gap and high temperature. Could also be cause by a tapered cylinder bore...Mule...

[cantho870]

well i found out after the fact that the cylinders were honed 005 over instead of bored. I also lost a lifter on that cylinder 3000 miles ago and it took out the cam. replaced all. I'm wondering if that is when my problen started.

[massheadcase1]

get your cylinders checked for taper..... with a dial bore guage....taper can cause a ring to break as it gets fatigued by getting big and small with every stroke......15k doesn't seem like much and the cylinders may look good...i have seen stuff w/less than 15k have lots of wear/taper..get 'em measured to be sure  ..Headcase

[jclark311]

I am new to the site, and have not rebuilt an EVO motor yet, but I have done a few hi perf v8 motors. It would seem to me that piston, and ring clearances on an air cooled motor are critical. If you are doing the top end of your bike, you must bore the old cylinders to make sure they are round and not tapered, use new pistons, and check ring gap to make sure its right. This is an air cooled motor with great changes in temperature, thats going to mean a lot of expansion, and contraction.

[Herbstr]

when pistons are fitted to the cylinder SE specifies the amount of taper that is required,

I would have to open a box of pistons to copy the specs

bored straight then honed to a slight taper

[Trip]

"Allowable".....not "required"....