02 426 timing help

13 replies to this topic
  • dubee

Posted December 07, 2010 - 09:22 AM


Ok so my bike stalled on me a lil while back it would get tight as if it was locked up and it would free up sometimes.. and its time for repair, but i took the valve cover off and flywheel plug to make sure it was in time before i tear it down and it looks like i am one tooth off?? auto decomp. is working fine no signs of wear or anything out of ordanary...??

Bike was running fine before this happended all it did was stall on me and i took a break for a sec and went to kick it and it was hard like it was locking up....then got it in the garge and it kicked over fine for a few...then tight spot!?:thumbsup:

Another problems is i bought bike used so i dunno how to tell if i got stock cams or its a 450 cam?:blah:

Anyhelp would be awesome!!!!!!

  • dubee

Posted December 07, 2010 - 09:29 AM


note there are 13 pins between the 12:00 marks but the marks will not line up with the head surface with both cams...

  • cowboyona426

Posted December 07, 2010 - 09:55 AM


If it has auto decomp, its not running the OEM cam anymore. Whether it was replaced with a OEM YZ 450 cam or a Hot Cams is the question. Sounds like an OEM 450 cam and I do believe you want 13 pins between the dots on the cam gears (look at the 450 cam swap thread to verify).
If the cams are in time, the lobes will point opposite each other when the piston is at TDC.

  • grayracer513

Posted December 07, 2010 - 11:57 AM


If the cam is an OEM YZ450 cam, it's supposed to be set at 14 pins apart from the intake cam, which is to be timed at TDC by aligning the I mark with the gasket flange on the head.

If it's a Hot Cams or other cam originally made for a 400/426, the it needs to be timed by using the timing marks: one at 12:00 and the other at 9:00 with the mark a 9:00 aligning with the head at TDC, and the intake timed as above. There should be 13 pins between the 12:00 marks, but this is NOT the primary reference for cam timing.

It's neither abnormal nor unusual for a AD YZF to feel "locked up" occasionally after a sudden stall. The engine may simply stop so quickly that the decompression pin is trapped behind the lifter because it didn't extend fast enough. Once you turn them through or back them up in gear a bit, they return to feeling normal:


  • dubee

Posted December 15, 2010 - 07:14 AM


If im at TDC and the flywheele mark is lined up the intake cam lines up great but then it looks like the exauhst is one tooth off (IF it is supposed to line up with the head like the Intake cam does?) My rod bearing is shot for sure.. bike was running great tell then, its not complete locked up but is obviouslly Locking up..lol if you know what i mean.

So could this thing have skipped a tooth when it stalled? i dont see how... autoDecomp. is working properlly and fine.

  • cowboyona426

Posted December 15, 2010 - 07:23 AM


It could have skipped a tooth, the cam sprocket could have slipped on the cam, or it could be a bad install.

  • dubee

Posted December 15, 2010 - 07:26 AM


this is what mine looks like

http://www.thumperta...ht=timing marks

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  • dubee

Posted December 15, 2010 - 07:27 AM


but my bike as always started fisrt second kick no matter what... and this is on tear down..

  • grayracer513

Posted December 15, 2010 - 08:06 AM


Once again, you need to find out whether the exhaust cam is genuine Yamaha, or an aftermarket cam made for the 426. If it's a Yamaha 450 cam, it has to be set up where the intake lines up as in the manual, but the exhaust is rotated one tooth farther forward. The fact that the bike starts well is a good indication that it's correct, because cam timing on these also affects the auto decomp feature, and if you're a tooth off it will either be nearly impossible to kick over, or have too little compression to start. Aftermarket AD cams time like the stock cams, with the marks aligned to the head.



  • dubee

Posted December 15, 2010 - 10:30 AM


gotcha! thanks alot guys!! just waitin to get bearings and im off to ridee!!

Thanks alot agian!!

  • dubee

Posted December 15, 2010 - 10:45 AM


also gray, do you know if the bone stock cams of the 426 are the same deminsions as in the two cam tubes, so what im askin is could i measure the deminsions of both of my cams and if there diff. sizes will that tell me for sure i have the 450 cam in it?

Im tryin to wrap my head around this sorry if you have told me this before somewhere.

  • grayracer513

Posted December 15, 2010 - 02:20 PM


The manual gives the following specs for the exhaust cams:

  • 31.2 ~ 31.3 mm (1.2283 ~ 1.2323 in) from base to top of lobe
  • 22.95 ~ 23.05 mm (0.9035 ~ 0.9075 in) across the cam at 90 degrees to the lobe centerline

  • 30.950 ~ 31.050 mm (1.2185 ~ 1.2224 in) from base to top of lobe
  • 22.494 ~ 22.594 mm (0.8856 ~ 0.8895 in) across the cam at 90 degrees to the lobe centerline

The chain will ride slightly higher on the Yamaha cam, too, and the overall finish of the Hotcams part will look a bit different from the intake.

  • dubee

Posted March 08, 2011 - 06:46 AM


thanks gary, almost got all the parts so rebuild will go quick once i begin!!!

  • grayracer513

Posted March 08, 2011 - 11:29 AM


Who's Gary?

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