need input

[chickwrench]

yzf250 w/262 kit seized

a few months ago, i got a big bore kit, ran awesome, then seized. i need help in deciding what to do. it is heavily scored on the intake side of my piston, cylinder, and the pin was wedged. also the cams (both) are ruined, and the vales are stuck because the seats for the cams are ground down and on them.

 

[chickwrench]

02 yzf250 w/262 kit. ran awesome, untill a shop changed cam timing, then motor seized. i need help in figuring what is fair and what is not. the bike was just a tad off (almost jetted incorrectly for altitude) b-4 service, but then seized the day we got it back. i had contacted the shop immediately, and they said it was due to the big bore kit. i don't believe that, cause the bike had the kit in it for about 4 months b-4 all this happened. does anyone have any advice on how to work this out?? Please help me, all i want to do is ride my bike.

 

[rickyd]

My feeling is they took in the job, so they should be accountable.. Was it there choice too change the cam timing?? Was that what caused the motor too seize??
Rick

 

[chickwrench]

when i took it in they said they would contact me with any issues they found, they called me and told me that the intake cam was off 1 tooth. they set it back to factory settings, called me and told me bike was fixed. i tool it home went for a ride and within 30 minutes the bike seized. i took apart top end to check for any problems, such as a broken ring(which is common on a big bore aftermarket kit), and found that the intake side of piston and cylinder, head were badly scored, ontop of the cams (both) in crooked and broken inside.

 

[chickwrench]

when you have such damage on the intake side of the piston and cylinder, it normally is caused by the piston being the wrong size, well the thing is that when i opened up the top end the cams were torque dwey too tight, when i confronted the shop, they said that it was not there problem. i have no i dea how to get my bike fixed.

 

[Jaybird]

The big bore had been in for 4 months? What did you have the bike in the shop for that would have them changing the cam timing? Why were they even inside the motor?

 

[Rich Rohrich]

Originally posted by chickwrench
i took apart top end to check for any problems, such as a broken ring(which is common on a big bore aftermarket kit),

I've put together quite a few big bore four-strokes and have NEVER seen a broken ring. Eric Gorr has put together more big bores than almost anyone and has never seen a broken ring either. It's hardly a common failure.

The piston problem you described sounds like a cold seizure which IS common if proper warmup of the forged piston isn't followed. Forged pistons expand more than cast pistons and they have to be warmed up slowly and carefully. If you ran this piston for four months without hurting the intake skirt you can pretty rule out an notions of improper piston/bore clearance on the initial build. Improper warmup, running the engine low on oil or some some foreign material in the bore are the more likely causes for damage to the intake skirt.

The cam caps seizing is a common problem with these engines if they aren't assembled correctly. That certainly sounds like the case with your engine. Lots of two-stroke trained mechanics crank down the caps and seize the cam bearing surface.

These bikes are remarkably reliable but they can't just be slapped together like our old trusty two-strokes. Proper assembly by a qualified four-stroke mechanic is one of the real speed secrets of thumpers.

 

[chickwrench]

the comment about the broken ring in the big bore kit, was not at all directed towards Eric Gorrs kit at all. i am just stumped on what to do. i took the bike in to the shop because i had just moved to reno from the bay area, and had a bogging problem that i could not fix with jetting, so i wanted them to look over it and let me know. when i took my bike in, that same day, they called me to let me know that the intake cam was off one tooth. they said they would put it back to the stock setting, and that i could pick it up the next day. so i did, when i had gotten back home, my dad and i went out for a ride, and the bike died right away, making a snapping sound. we called my husband to come pick up the bike and then notified the shop. they said bring it in and show us. i did, but they told me that just because they were the last shop to work on it, that they really could not prove what caused it. i can take pictures of all my parts if that would help in determinig what really happened.

 

[Daisycutter]

What was your "warm-up" procedure. I've read that intake side piston smearing can frequently be attributed to improper cold-starting/warm-up.