Cams and Top End

5 replies to this topic
  • jonova

Posted June 08, 2005 - 01:51 PM


I am just about to pull my motor apart and put in some new hot cams and a 97mm piston in my 01 426. I have a few reservations left that I want to clear up.

When I tear the motor apart at TDC and then replace the cams, piston and new barrel, how do I know if the bike is at true TDC without the cams in the bike? Do I just have to make 100% certain that the entire time I have the motor apart the crank does not move at all?

Do our bikes fire both on power and exhaust stroke?

  • 02YZ426

Posted June 08, 2005 - 01:59 PM


Just look through the inspecion window on the side case... as long as the mark on the flywheel is ligned up with the mark on the case then its still at TDC. Just look in your manual, it shows it all in detail. IF you dont have a manual there is one somewhere in this forum free to download, just do a search and you should be able to find it.

  • jonova

Posted June 08, 2005 - 03:18 PM


I hear ya on that....But, this is a True TDC which is when the plug fires and then there is a TDC for the exhaust stroke and they are 360 degrees off. How do you know you are at True TDC, because all that mark does is tell you the piston is at the top of the stroke. :)

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  • 02YZ426

Posted June 08, 2005 - 03:54 PM


Thats because it doesnt matter... the cams determine wether or not its intake or compression stroke, Just make sure the "E" mark is facing exhaust and the "I" mark is facing the intake side and the marks on the flywheel line up with the case.

  • grayracer513

Posted June 08, 2005 - 04:14 PM


The ignition is crank triggered, and thus produces a spark on each TDC, so both TDC's are the same as relates to ignition timing. "True TDC" has nothing to do with which stroke the engine is on, though, only on whether it is within one degree of TDC or not. The crank determines that. The cams and ignition must be sync'ed with that to determine which TDC is which in terms of the engine cycle events.

  • jonova

Posted June 09, 2005 - 06:49 AM


I see clearly now, thank you Masta! :)

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