YZ426 rattle noise after rebuild. Help Please.

10 replies to this topic
  • Dennish87

Posted August 17, 2013 - 06:16 AM


When the transmission went out on my yz I put a new transmission it it and shift fork and it still slipped in 5th gear. Then I put a different bottom end on my yz426 because the parts to fix my tranny was as much as a used bottom end on ebay.  I had to use my old cankcase side covers (Left and right).  I installed everything correctly but after putting it all together there is a rattling noise coming from what sounds like the kick starter. It never did that with my old bottom end.  I also used a different exhaust cam because a bird took a crap on it and it actually pitted the metal on my cam. Other than that, the top end was unchanged.  The top end is completely rebuilt.  New timing chain, valve seals, springs, piston, wristpin and circlips.  It sounds like it's coming from the right side and somewhere in the bottom end but its hard to tell.  It's not a "OMG this things going to explode" sound, more of an annoyance because I know it didn't do it before I replaced the bottom end.  Here's a video of what it sounds like.  I might try to get a better one later.  It's a little distorted because it's inside the barn.  





This is someone else's video but it sounds very similar to what mine does. 




Here's a pic of the bike. 



Edited by Dennish87, August 17, 2013 - 06:18 AM.

  • jwleonard

Posted August 17, 2013 - 05:39 PM


I've never heard this sound before so I have no experience with it and this is just a guess but the first things I can think of are the kick start assembly & shift mechanism.  You could try starting it and moving the kick starter around (through the kick cycle) to see if the sound comes & goes or changes any.  You could also put it in gear and/or ride it and put pressure on the shift lever to see if it changes any.  Just be aware doing these could cause complete failure too since you really don't know what is causing it right now.  One more option would be to look into removing the kick start (internal parts too) and then bump start it and see what happens to the noise.  I'm not saying this is even possible; I'm just saying look into it as a possibility.

  • Dennish87

Posted August 17, 2013 - 06:18 PM


Well when you press on the kick starter while its running it will grind like crazy and that's kinda the noise its making. I think I'm going to take the right side cover off and check to make sure the kick starter is installed correctly and also check that the clutch basket but is secure. Also will check the counterbalance key and nut. I've heard they can come loose and make all kinds of noise.

  • Dennish87

Posted August 19, 2013 - 04:24 AM


Anyone else have an idea what this might be?

  • ekulb14

Posted August 19, 2013 - 07:21 AM


cant see from the pic but do you run a skid plate ? ive seen and heard thoes rattle something terrible, exhaust's too, and let us know how it runs with out the kick starter

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  • Dennish87

Posted August 19, 2013 - 10:18 AM


I took the skid plate and water pump guard off and it seamed to resonate a little less. Not really sure how I'll get it started without the kick starter. Might have to have a buddy pull start me.

  • Dennish87

Posted August 19, 2013 - 10:19 AM


I did repack the silencer, but there shouldn't be anything rattling in there.

  • Dennish87

Posted August 26, 2013 - 08:11 AM


Grayracer513 do you have a comment?  I still haven't figured out what this might be.

  • grayracer513

Posted August 26, 2013 - 08:24 AM


No.  I can never make anything of noises recorded and posted in videos or whatever.  Too many distortions between the low quality mike that did the recording, the acoustics of the place they were recorded, and the sound reproduction at the other end, plus all the steps in between.  Just all sounds the same to me here, so I never bother to listen.  Checked yours the other day, same thing.  Can't tell anything from it. 

  • WGP

Posted August 26, 2013 - 04:30 PM


Maybe head pipe not tightened to motor? I did that but it sounded more clanky then your sound.

  • MotoRoku

Posted August 27, 2013 - 10:12 PM


What year is it?  If its a 2000, I would check the primary drive key for any wear.  My 426's key was a little beat up and made a lot of noise, changed the key and sound went away.  

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