2000 yz426 engine? slapping noise

4 replies to this topic
  • ssewards

Posted April 13, 2008 - 05:51 PM


i had my 426 out for the first time today. when the bike was hot and running i would hear at low speed a slapping noise possibly from the top end area. also the bike would just stall every once in a while. i have never had the top end apart. i just changed the oil and filter and the spark plug. the outside temp was approx. 56deg. farenhiet. could this possibly be piston slap or a timing chain streched ?? thanks for any help. oh yeah the bike rips and i smoked all the 2-smokes out there today.

  • BRYANS01

Posted April 13, 2008 - 07:10 PM


the timing chain would have to be bad enough that it would have already jumped a tooth and even then i dont know if you would be able to hear it. these things hate a bad adjusted drive chain and yes at low speeds in any gear they will slap like crazy i would check that before anything.

just read you post again do you mean speed or rpm in nuetral, the jd jet kit will stop the stalling prob. you have it did mine.

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  • 06crf_er

Posted April 13, 2008 - 07:15 PM


Inevitably it was chain slap. Very very common when lugging a 4 stroke. Did it make the sound when stationary and being revved? If not, check your chain tension to make cure it's correct, then if it is, get used to it. Pretty much par for the course:thumbsup:

  • Ga426owner

Posted April 14, 2008 - 06:22 AM


Can be chain slap or worse......a 4stroke bike with a lot of hrs needs to be checked. Again it can be a bearing issue or not but it needs to be checked before further catastrophic damage can occur...once this happens...expect a 2000.00 repair bill or more....this is why they are all timebombs. It is only a matter of time before they will detonate.....in yamis case hopefully a lot of time:excuseme:

  • grayracer513

Posted April 14, 2008 - 09:34 AM


It makes a difference whether you are hearing this noise at low engine speeds such as at idle, or at low speeds under a load.

In the first case, it could be just the usual cacophony of noises that these engines are notorious for. But there could be a problem, too, so it's a good idea to compare it to another 426 to see how much it sounds like all the rest or not. If it's a 2000 model, it could have a loose nut on the primary drive gear, which would let the balancer drive gear rattle on the key that holds it. If that's the case, it's fairly urgent that you fix it, but your parts bill will be about $10, including a gasket, not counting coolant.

If you here the noise under a load, it's more likely the rear chain slapping the swing arm. Normal, and nothing to worry about.

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