2001 yz426 feels like no compression after rebuild I'm stumped

21 replies to this topic
  • joelenway

Posted October 03, 2014 - 06:36 PM


OK so I had my crank rebuild new cylinder new piston put it all back together and I can push the kick start with my hand.. timing is on I and dot aligned with the head. I put a teaspoon of oil in thei plug hole kicked and kicked but no resistance.. valves were cleaned checked everything was in specs.. where do I go from here need help!!!

  • joelenway

Posted October 03, 2014 - 06:37 PM


Bike has hot cam.

  • mch

Posted October 03, 2014 - 07:09 PM


Just to be clear.  Is the crank turning and is the spark plug in?

  • joelenway

Posted October 03, 2014 - 08:44 PM


Yes spark plug is in. And yes the crank is moving..it has spark it has gas but I but I can push threw the strokes with my hand it's that easy. It feels the same kicking it over with the spark plug in or out..

  • Slow and Jerky

Posted October 04, 2014 - 04:23 AM


Check your decompression cable and make sure it is not too tight and holding the valve open. Other than that I would suspect the valve timing is off.

  • MattyDubz426f

Posted October 04, 2014 - 04:43 AM


I had my cable get tight on me once. Whenever I would turn it would kill out. Was vary confused for alittle before I found it.

  • joelenway

Posted October 04, 2014 - 05:55 AM


The cable is very loose and when I kick it over I can feel the Decompression lever Get Harder And softer.. Could It Possibly Be 180 Degrees Out Of timing? But wouldn't it still be hard to kick over I mean it feels like I'm kicking it over without the spark PLUg In Its That easyeasy

  • Slow and Jerky

Posted October 04, 2014 - 06:06 AM


No compression has to be one of two things, air leaking past the rings or the valves. Assuming there is not a gigantic hole somewhere, the valves are the  most likely culprit. It's easy to get the timing off enough to cause serious headache's. I always check TDC with a probe of some sort just to be sure and double check that the cam lobes are pointing away from each other  when you have the marks aligned with the head and that you are looking at the correct marks.

  • joelenway

Posted October 04, 2014 - 06:39 AM


So where do I start with the valves? All the clearances with the shims were perfect

  • dkbl5

Posted October 04, 2014 - 06:43 AM


That decompression setup is where I would start - check it out end to end.

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  • amamx19

Posted October 04, 2014 - 08:35 AM


Do you have exhaust cam lobes pointing to the front of bike and intake cam lobes pointing to the rear? I have Hotcams and got confused on all the alignment dots.

  • mch

Posted October 04, 2014 - 10:05 AM


Take some pictures of the of the cam timing marks to show us.  Also, drop a chopstick or something down the spark plug hole to make sure you are at TDC and make sure the bottom marks line up per the manual.

  • joelenway

Posted October 04, 2014 - 10:59 AM


[attachment=187867:20141004_135033.jpg][attachment=187868:20141004_135122.jpg][attachment=187869:20141004_135141.jpg] here are some pictures

  • joelenway

Posted October 04, 2014 - 11:10 AM


The dots don't line up exactly with the head. I moved it one tooth and it was worse the other way. So that is as close as it gets

  • joelenway

Posted October 04, 2014 - 11:37 AM


Decompression valve is working perfect I can see it engaging and releasing..

  • joelenway

Posted October 04, 2014 - 11:39 AM


I have not got it started since I put it together.. should I keep kicking it to see if it starts and maybe the piston will seat??

  • mch

Posted October 04, 2014 - 11:43 AM


It looks right, check this video on the lobes pointing out.. 

  • joelenway

Posted October 04, 2014 - 12:02 PM


Don't really know what happened but said screw it I'm gonna put it back together and bring it into the shop. Got it all together kicked it one tim it ztarted right up.. LMFAO!!! TIME to break it in..:)

  • AFelix

Posted October 06, 2014 - 03:29 PM


Correct me if I am wrong, but it looks like you have a decompression cam? Why do you have the decom. lever still?

  • joelenway

Posted October 06, 2014 - 03:59 PM


When I bought the bike the guy told me even with The decompression cam he needed the lever to start it.. well after I rebuilt it obviously it doesn't need it and I don't have a plug for it so I just left it.

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