Nah its never 'blown up' on me. I just rebuilt the top end with a Wiseco Pro-lite piston and new hone job.

First ride: at night around 70 degrees, for about an hour. Went wide open, 'break it in like your gonna ride it' method.
Ran great.

Next day. 100 degrees. Wide open again. Ran for about 10 minutes... BOOM.
(well, knock knock knock knock........ anyway)

the motor became VERY loud, so I pulled the clutch and it came to a loud, knocking stop,

Uppon kicking the kickstarter, the motion is smooth untill it hits 'something'. Then its BAM.
Its not seized. The piston is free. I can put it in gear and rock it back and forth, and the motor turns till
it hits whatevers lodged in both directions.

What do you guys think went wrong?
I was told today that the Pro-Lite pistons need a slow, under half throttle break in.
Deff. NOT what I did today.

What do you guys think?


ps. To you Beechman... (because I told you id tell you the results)

My Zilla WALKED on that modded CR250R in a drag on pavement..... before it blew up.

 

I assume it has a bent connecting rod.

 

or you seized the lower rod bearing. i had that happen on my buddy's kx250 and thats how it acted.

 

Something simialr happen to me,but i just bought my quad like 2 weeks ago and i started up and made sure everything was fine and i loaded it up in the truck and got to my ridin place.WHen i got there i started it up let it warm up for about 2min.took off down the road and turned open up the trottle in 3rd and than clonk clocnk .stopp...........that was a hell of a ride.i knew that didnt sound good so i also tried to kick it and it was easy .to easy.and then stopp.obvioulsy the rings were shot.and that thing ur talking about when u try to kick it it stops my problem was the piston bushing or washers that stableise it.one of them broke and went down in the eng and lfew up in the ports. and came on top of the pistoon and went inbetween the cyclinder and piston.
basically i got messed up.Try looking for some washers.

 

i know it doesnt help but the break it in like your gona ide it is a 4 stroke thing and thats usualy going against manufacturers recomendations,

only ever had 1 engine go on me, RGV250 road bike, total meltdown and seizure at 90mph 300yd black streak down the motorway from my rear tire,

ally piston melted all over my polished and ported nicasil bore,

ISNT AUTO LUBE FUN?? EH!!!

 

sounds like you broke your connecting rod. remember you always have to take it easy for about 3 tankfulls until you give her hell.

 

Honestly, "breaking it in like you will ride it" is stupid. You shouldn't do it to any motor you will be keeping. AT LEAST let them break in for 2 hours, with at LEAST 2 cool down sessions. May have saved you $2-300, depending on what other damage you did. Good Luck.

 

Thanks.. Im aware of that now.

 

damn the bad luck. i always whetehr its a 4 or 2 stroke i prelube the entire motor when assembling that really helps breakin my guess is u used a stock bore in old condtion and the cylinder was out of round u cracked the new piston due to all the stress being on 1 side of the piston.. if u did use a new bore with the new piston imma say the bottom end let go probably the rod bearing.

 

1) Did you mic the cylinder or just assume it was fine?

2) Are you using race fuel or at least a race fuel/premium fuel mix (even stock LT500's are prone to detonation)?

3) Did you do a leak-down test after final assembly and before first start-up (very easy and great insurance)?

4) You didn't mention making any plug/piston readings or consulting an egt. Do you just assume the jetting is fine?

Let us know what the piston looks like (if and where melted or broken). The motor might be turning over freely untill it hits an aluminum patch imbedded on the cylinder walls.