426 problems timing... i think


9 replies to this topic
  • Rcme86

Posted March 05, 2008 - 11:58 AM

#1

okay, i must have messed up somewhere or my valves were bad... this is the first four stroke ive every worked on (besides my truck). So i got everything back together(the timing jumped so i took the head off), got the timing all dialed in (so i thought) and was all pumped up to take it for a ride and i started kickin it over and i noticed it wasn't getting that really big build up of compression like it used too. I dont have to use the compression release to kick it over. So im wondering if i missed something... i checked all the valves with starting fuild and none of them leaked it out. So is my timing off? i think when i get it fixed i might consider going back to two strokes lol.

  • 642MX

Posted March 05, 2008 - 12:04 PM

#2

What was the cause of it jumping time? Can you take some pictures of the cams and the lower flywheel mark?

  • Rcme86

Posted March 05, 2008 - 01:55 PM

#3

I think the chain stretched. here are some pictures... im having trouble understanding the timing thing in the book so maybe someone on here will have some pictures or can help me out.
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  • 642MX

Posted March 05, 2008 - 02:34 PM

#4

On the intake side, it looks like the cam gear has rotated on the camshaft. The marks on the gears appear to be correct, but the intake lobes are facing down when they should be angled up just like the exhaust side.

I'd replace both cams. Stock cams are a dime a dozen on ebay, or you can upgrade to Hot Cams and not only will you gain more power, but you'll gain auto-decompression like the 450's have.

  • grayracer513

Posted March 05, 2008 - 02:39 PM

#5

If the mark on the flywheel and the pencil in the plug hole agree that you are at TDC, then you have it timed correctly according to the marks on the sprockets.

However, it looks to me as if your intake sprocket has slipped on the cam. If you look at the picture of the right side, opposite the sprockets, note the angle of the exhaust cam lobe. Your intake cam should be a mirror image of that, pointing up and back at about the same angle as the exhaust is facing up and forward, but it isn't.

You could have the cam reindexed and tack welded, but the cost of that will likely exceed the cost of just buying a new one. IMO, you need a new intake cam, and you will want to recheck that your intake valves have not hit the piston.

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  • tnl

Posted March 05, 2008 - 04:52 PM

#6

Looks like the punch marks are not even? But, if the piston is at TDC then I guess it's a cam prob.

  • Rcme86

Posted March 05, 2008 - 05:16 PM

#7

Oh man... thanks so much i would have never of figured this out. So my next question is what would cause it to slip like that? and should i buy both the exhaust and intake cams? and are the hot cams worth it?

  • 642MX

Posted March 05, 2008 - 05:36 PM

#8

Oh man... thanks so much i would have never of figured this out. So my next question is what would cause it to slip like that? and should i buy both the exhaust and intake cams? and are the hot cams worth it?


Not sure why it slipped, but I would replace the exhaust cam too. Its cheap insurance.

Yes, the Hot Cams are worth it. They provide gains throughout the power curve and the decompression feature is the best mod you can do to a 400/426.

  • grayracer513

Posted March 05, 2008 - 06:47 PM

#9

... what would cause it to slip like that? and should i buy both the exhaust and intake cams?

It happens now and then for no apparent reason, but you might want to look to see if the intake seized in the head once (which is also repairable).

  • Rcme86

Posted March 05, 2008 - 11:33 PM

#10

hmm, okay well hot cams it is. thanks alot for the help.





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