trans issue 06 yz450

I know there has been a ton of threads around the trans for these bikes but I think my problem is a little different than the common issues. I did some searching but didn't find exactly what I was looking for.

This is a new to me bike as of a few months ago. I put brand new chain a sprockets on it this season and had about 4 rides on it. Wanted to take the bike out for a trail ride this weekend and was just warming it up down a dirt road. I was not getting on it hard at all and had just shifted 4th gear and the chain snapped and the motor died.

It broke the lower bolt boss for the chain guard which put a hole in the case. (I can take care of fixing that part).

My concern is that the bike is REALLY hard to shift now. Both when it's running or when I dry shift it on a stand. I had to rock it back and forth for quite a while and apply way too much force on the shifter to get it to go through any of the gears.

It looks like I'll be pulling the motor and getting in to the trans.

My question is what came first here? Did the chain break causing the trans to lock up? Or did the trans lock up causing the chain to break?

I would like some suggestions to get at the root cause here so neither of these things happens again!

Also what should I be on the look out for in the tranny. bent shift fork maybe?

Thanks for any help.

If it was the OEM chain, it's almost certainly the cause of the whole problem. My first guess in a case like this would be that the shift shaft was bent by the chain. Remove the right side cover and the clutch, then pull it out and have a look.

Thanks Gray!! exactly the kind of starting point I was looking for. I was really hoping you would reply. That makes a lot of sense. The Chain was crammed up in front of the shift lever and the lever itself has some scarring on it!

It was a DID 520 chain though! I'll have to look at the exact model when I get home today but it was supposed to be the recommended chain for the 450's.

would you still be inclined to say that the chain was the cause of the failure? If so should I assume that it was a fluke or is there maybe an underlying issue with alignment. The chain was tensioned properly and the masterlink was correct.

Thanks again!

The two most common causes of chain failure are the tension being set too tight, and the master link being turned around backward, or, in the case of the press fit master links, not pressed together far enough to allow the clip to seat completely in the grooves in the pins.

Since you say you did neither of these, I have no idea, but I wish I had $5 for every time I've caught someone with an '06-'08 YZF with his chain too tight.

Also be sure and check the Shift Index Arm:

http://www.thumpertalk.com/forum/showthread.php?t=744166

He may as well while he's in there, but that condition is unlikely to produce the symptoms he has, and even less likely to be caused by a chain failure.
The two most common causes of chain failure are the tension being set too tight, and the master link being turned around backward, or, in the case of the press fit master links, not pressed together far enough to allow the clip to seat completely in the grooves in the pins.

Since you say you did neither of these, I have no idea, but I wish I had $5 for every time I've caught someone with an '06-'08 YZF with his chain too tight.

I've never had problems with breaking chains before. Is this a common problem on the 06-08's?

Just as an update, I got the shifter shaft out tonight. It does not appear to be bent.... :banghead: (moved freely in the bore and I rolled it on the bench)

I'll be delving deeper in to the trans tomorrow night. What would be the next logical place to look for damage?

Thanks

I've never had problems with breaking chains before. Is this a common problem on the 06-08's?
It is in the sense that people tend to judge the chain tension by how it looks rather than measuring it out as the manual calls for. And the '06+ requires more slack than previous models, and looks loose to most people when properly adjusted.
What would be the next logical place to look for damage?

You'll have to "play with it" to see what's binding up. Your problem could be that the shift rail pocket(s) in the left case for one or more of the forks is damaged.

Thanks again for all the help. I'll let you know how it turns out!

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