No compression after replacing cam chain


9 replies to this topic
  • marbee40

Posted July 28, 2012 - 12:35 AM

#1

2001 WR426, no mods.

Bought this year. Ran like a champ after cleaning carb. I'm the 2nd owner.

Two weeks ago, bike stalled, no compression. Pulled apart. Found two pieces of the little cam shim laying down below the rotor (flywheel?). Didn't know what the metal was, but it definitely broke the cam chain. Popped the covers off the cam and found one shim correctly in place above each cam. Original owner (or mech) must have dropped one at some point and neglected to go after it. :-(

Pulled head and cylinder. Piston and valves look to be in excellent condition. Did NOT pull valves, just looked at all five plus piston. Didn't appear to be any damage.

Put on new cam chain, set piston TDC, put cams on correctly per the manual. Put it all back together. When kicking I get no compression...ie when kicking, the kicker doesn't come to a stop, requiring the use of the compression lever on the bar. Used to start 1st time, every time.

Ideas? Is it possible the previous owner had the YZ timing (rotated exhaust cam one tooth clockwise) and now it won't start cuz I have is set to WR stock? Maybe a bent valve that I can't see unless I pull them out?

THanks,
Jim in AK

Edited by marbee40, July 28, 2012 - 12:37 AM.


  • GuyGraham

Posted July 28, 2012 - 12:50 AM

#2

Sure the 'pieces' you found weren't woodruff keys?

Is the cam chain rotating the cams when you kick it over?
YZ or WR timing will not result in no compression

Edited by GuyGraham, July 28, 2012 - 12:52 AM.


  • MANIAC998

Posted July 28, 2012 - 03:45 AM

#3

Have you measured the valve clearances? I'm willing to bet that you'll find one or more with no clearance, and this will be the cause of no compression.
Maniac

  • marbee40

Posted July 28, 2012 - 05:14 PM

#4

Guy, Nope, woodruff key is good. Yes, cams are rolling.

Sure the 'pieces' you found weren't woodruff keys?

Is the cam chain rotating the cams when you kick it over?
YZ or WR timing will not result in no compression



  • marbee40

Posted July 28, 2012 - 05:19 PM

#5

After fussing around for 4 hour (yes Im slow) ive come to the conclusion it must be valves. Im dead nuts on with cams being set propely at TDC using the manual. Dammit. Bet I tweaked a valve or two. IF, for some odd reason, all valves are good, can u think of anything else Im missing b4 I order new valves? Finally, if it IS valves, should I upgrade or go stock? Ive read about kibblewhite. Also, should I just order new shims? Anything else while Im in there (again)?

Thanks guys!

Have you measured the valve clearances? I'm willing to bet that you'll find one or more with no clearance, and this will be the cause of no compression.
Maniac



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  • marbee40

Posted July 29, 2012 - 03:57 PM

#6

Just did a leakdown.  Poured some gas in intake side.  One of the valves weeped.  Cleaned carbon from surface and tried again. Came pouring out.  Must be it?

  • AKmud

Posted July 29, 2012 - 05:03 PM

#7

I'm helping Marbee with the project... What is the general rule on replacing valves? Can we get away with just changing the one or do they all need to be done at the same time? The little buggers are a bit spendy.....

  • MANIAC998

Posted July 29, 2012 - 07:36 PM

#8

You should be able to just replace the bad one. I see no need to replace the others. Hopefully you checked valve clearances before tearing the engine apart. This would tell you if the others were running tight and might need replacement.
Maniac

  • marbee40

Posted August 02, 2012 - 03:36 PM

#9

We didn't but I'm replacing the two outside intake valves. Our local Super-Bike-Mech looked at the head and vavles and explained that all valves (other than the two bent ones) were still in excellent condition. Just waiting for the new vavles to come in and put this monster back in action before our short AK summer is over. :)

  • ncampion

Posted August 04, 2012 - 10:23 AM

#10

A broken cam chain will almost always result in one or more bent valves.




 
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