last race of the year. oops..

[sborns]

ran real well this year with the old yb quad now my buddies. threw on the o'connor YB killa cylinder and this happened on the last practice of the last race of the year. the one thing i cant explain is the carbon on top of the piston. but here is the damage.

intake side

exhaust side

wierd carbon build. the clearing is on the intake side.

 

[blasterBruce]

Looks like too much Cylinder to Piston clearance caused the ring to come loose or catch on a port

 

[sborns]

well what gets me is the top rig spun from the pin and got caught on the exhaust port. and sorry bout the photo size i tried to get them smaller but couldn't for some reason.

 

[blastblast2]

Man that sucks how bad did it eat up the jug

 

[sborns]

Man that sucks how bad did it eat up the jug

not too bad actually. it moved material from the exhaust port into the cylinder but it shouldn't take too much to get cleaned up.

 

[sporty982000]

that should not have happened.

if the chamfer was good, should not have caught. and the ring moving, makes me wonder how that happened, unless it slipped / moved, while putting it into the cylinder.

or out of spec piston to cylinder wall clearance.

Sporty

 

[sborns]

the piston was a 67.25 and cylinder i just measured at 67.30.

 

[blastblast2]

At least you can save it

 

[Awk08]

that looks to be an excess of carbon buildup, what oil and ratio are being run ? possibly running rich ?
what's a plug chop show ?
possibly had a ring locater pin failure ?
what brand piston ?
how many hours on that set-up ?
quite possibly just worn/run past clearence specs

 

[sborns]

32:1 yamalube 2r
plug chop i couldnet tell you i wasnt involved in tuning or the build. i was away at school.
locating dowls look to be recessed way in the back of the ring groove.
wiesco.
100-200 hours? flattrack so wide open turn left.

 

[Awk08]

100-200 hours on a raced engine is way too many without at least re-ringing it a few times.
measure the width of those rings compared to new ?

 

[sborns]

one ring gone. the other im working on peeling out as i type. im thinking that the locating dowl is set to far in the piston and not holding the rig in place.

 

[sicivicdude]

one ring gone. the other im working on peeling out as i type. im thinking that the locating dowl is set to far in the piston and not holding the rig in place.

Wiseco pistons use a recessed locator dowel with full face rings. The recessed dowel pin design works well as long as the piston to cylinder clearance and ring thickness are within tolerances.

Awk's right, 100-200 hours is too long on a race engine without a re-ring. With a good (power wise) exhaust port width, the rings will be sticking out into the exhaust port while it's running and will be pushed back into the groove with each stroke. That will wear the ring thickness down until it's no longer tight against the locator pin and eventually one end will "pop out" and the result is what you have.

I do not believe that carbon buildup is excessive though. That's fairly normal on a seasoned setup and I've seen engines with WAY more carbon buildup on the piston that didn't do what yours did. Twostroker99's piston was original factory 66mm ART cast piston with WHO KNOWS how many hours on it and had lots of carbon buildup on it and was happily ticking away.

 

[sborns]

well in that case were going to be keeping a closer eye on it next season. see if i cant somehow but an hour meter on the thing. thanks for the input guys. now to see if ken can possibly squeese a little more out of this cylinder!I:I

 

[eventhorizon]

thanks for all the info guys its my quad that this thread was about since buying it from yb200 late last year and putting the oconner worked cylinder on its been amaizing

 

[sicivicdude]

the piston was a 67.25 and cylinder i just measured at 67.30.

Blaster piston's for a 67.25mm bore will actually be 67.20mm (.002" or so smaller than the "stated" size). If your cylinder was 67.30mm and your piston is 67.20mm you've got .004" clearance. Add that to the high time on that engine which has probably worn the rings enough to slip past the locator pin and there you have it....

 

[little3mil]

Blaster piston's for a 67.25mm bore will actually be 67.20mm (.002" or so smaller than the "stated" size). If your cylinder was 67.30mm and your piston is 67.20mm you've got .004" clearance. Add that to the high time on that engine which has probably worn the rings enough to slip past the locator pin and there you have it....

sounds like you found your problem