2006 YZ450F No power on low end

2 replies to this topic
  • Raptor_rider1985

Posted June 09, 2016 - 12:06 PM


Hey guys.

Recently I had my intake camshaft seize up and I bent my intake valves on my 2006 YZ450F. When i took it apart I noticed the cam journals had some scoring on them.  I took my head to a local engine shop to see what they could do.  They polished the journals and the camshaft and got the cam turning perfectly again, they think i overtorqued the caps last time i had the head off.  They installed 3 new intake valves, valve guides and seals.  They adjusted my valve lash to spec and i took the head home and installed it.  I installed the head, turned the Crank to TDC, aligned the camshaft gear punch marks on the top of the cylinder head.  I double checked valve lash, which was perfect and put everything together.  When i started the bike it ran very poorly.  It usually starts first kick and idles perfect.  I took it out for a quick spin and had no power on low end, however had decent power from half throttle onward.  The bike would actually almost stall if i didn't rev up before releasing the clutch. I took the valve cover off to verify i timed it correctly, which it was, however i noticed the intake lobes were sitting at about 9 oclock when looking at the engine from the right.  When typically i remember them pointing at 10.  I took a photo.  Can anyone confirm that this correct or incorrect? I'm assuming the gear spun on the camshaft? Does anyone have any pictures or documentation on how that gear should be indexed on the camshaft?CAMSHAFTS.jpg

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  • grayracer513

Posted June 09, 2016 - 12:45 PM


Retarded.  Your intake cam, that is.  Assuming your timing marks are aligned, your intake cam sprocket has slipped on the shaft.  You could try advancing it one tooth, but there's no telling, and no reason to believe, that it slipped exactly one tooth's worth, or that it won't slip again, now that it has once. 


To properly re-index it, you first need the stock opening-closing specs, then a degree wheel, then a hydraulic press.  You'll need to remove and replace the gear more than one time, most likely, to get it back where it belongs, then you'll have to tack weld it in place to prevent it from slipping.  At the end of that operation, you'll have a correctly timed worn and damaged cam.  Why bother?  Simpler and cheaper to replace the cam unless you have all the stuff to do it with.

  • Raptor_rider1985

Posted June 27, 2016 - 05:46 AM


Thanks Gray. Advanced my intake shaft 2 teeth on the gear. Runs like a top.

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