2000 YZ426 Noises!

Ok, today a 2000 YZ426 came on my local craigslist for cheap so I went to check it out. It was making alot of noise that it wasn't supposed to. I know this because I just sold my perfectly running 2000 YZ426 about 3 days earlier, and it didnt make noises like these. I know that they have a few issues since they were the first year design but I'd like to know more about exactly what the issues are. I've read thread after thread and don't quite understand it all. I read that having aluminum skid plate on the bottom made the noise quite a bit louder, so I took this off and it made it about 1/2 as loud so I could diagnose the noisy area a little better. It runs strong, has no issues starting or running or even idling, but it makes alot of noise. The noise seems to be coming from the bottom of the engine, noise on both sides, but if I had to pick one I think the noise would be louder on the clutch side. I havent been able to figure out what exactly the weak link on the 2000's is in there and what I need to look for when I pull off the cover. I also am going to check the water pump, because I've read about those as well. It shifts through all gears, rev's high and grunts low but the noise is killing me. The guy I bought it from said that he's been riding it like this for the 5 years that he's owned it without any problems, but I just can't handle it. any diagrams pointing the the weak part(s) would be AWESOME! or any other ideas would be alot of help. Also, I think that the noise becomes louder when the bike is at an idle than when it is moving, hot/cold engine doesn't change the noise. Thanks for any help!

Your clutch basket could be worn. If you pull in the clutch does the noise get quieter??? How low is the idle set that can cause some weird noise as the motor is fighting to stay running.

I didn't notice the noise get quieter when I pulled in the clutch yesterday, but I wasnt exactly thinking of that. I'm gonnna go fire it up in a few hours and I'll see if anything changes when I pull in the clutch, I don't think it will. It's a fairly loud noise, like a clanking, but it's in the bottom of the engine, so I don't think it has anything to do with the valves, cam chain or any piston slap, especially since it runs so well. Thanks for the idea, i'll check it out.

I think something that sounds likely and is also a problem on these bikes is a key being loose on something. I have been looking through my manual trying to match up what people are saying to the pictures in the book, and i think the one that people were talking about is the number 6 shown in this diagram. if i'm wrong please let me know so I wont be wasting my time in the bike.


Sounds suspiciously like the counter balance gear key as you mentioned. This had to be replaced on my '00. When it was loose, it sounded like the whole bottom end was ready to explode. Replace one little key and the noise went away. I'd start there.

so am I right in my guessing that the number 6 in the diagram is the correct key to be looking for? I don't have much time inside an engine yet so the more direct I can be the less chance I have at breaking something I don't know about. Thanks again, TT has yet to let me down on any of my problems.

Yes, #6 in the diagram you posted.

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