help on a timing chain

[backwoods boy]

i bought a bike [beartracker 250] that i believe has a broken timing chain when you try to start it you can hear a clunking kind of and the top end was just rebuilt so now im trying to figure out wat to do with the bike yamaha wants 250 just to confirm its the timing chain can anyone kind of explain wat all goes into changing one
                                                                         thanx in advance

[TRX450R_Racer]

If the timimg chain was broken you wouldn't hear anything from the top end. The timing might be off. If you are mechanically inclined, you can do it yourself. You need to get a service manual. that will make it easier.

[backwoods boy]

ohhhhhhhhhhhh someone told me that if it was making the noise with the sparkplug out then it was the timing chain because a valve wouldnt when the sparkplug was out ??

[TRX450R_Racer]

ohhhhhhhhhhhh someone told me that if it was making the noise with the sparkplug out then it was the timing chain because a valve wouldnt when the sparkplug was out ??

The timing chain goes around a gear that is attached to the cam. When the cam turns, the lobes on the cam open and close the valves. If the chain is broken, it will not turn the cam. That means not action up top. It will turn it until it all comes off the top gear. Maybe 1 to 1 1/2 revolutions. After that it will bunch up in the bottom end and lock up the motor. If you were closer I would look at it for you for free.

[backwoods boy]

wish you where closer lol but ya its all good i didnt pay much for it just an extra bike
ya when i got it the top end had just been rebuilt but the guy said it had a bad valve ? would that make a click/cunking when im trying to start it?

[TRX450R_Racer]

No.
A bad valve usually leaks down. I think maybe the timing cahin is stretched and jumped a tooth. That would make the valve open when they are not supposed to and possibly hit the piston. It's hard to tell with out tearing into it.

[Turboderf]

if its making noise thats not good something is hitting

[backwoods boy]

oh well thanx guys for the info looks like she'll be up for sale 

[Fox17]

the bike turns over it just wont start. its probably a timing issue. we will look at it when we get the 400ex fixed. its more important. it wont take much to check the timing. the XR was very easy to get to that part. if its 3 times as hard it will take 30 mins tops to get in there.