Yz 426F Camshafts


7 replies to this topic
  • 3d0

Posted September 30, 2013 - 05:08 AM

#1

Hi guys, I'm kinda new here, been lurkin around a lot reading before I had to ask for advice.

So I've been rebuilding my yz426f 2001 from bottom up. I guess it skipped a toothe or dropped a valve and the piston slamed on the valves, choping some of them completely off.

I bought a used 02' head which included everything, Ti valves, springs, camshafts etc.

Did the bottom end, bought new piston and rings, installed everything. Checked the clearances, the exhausts are .25 and the intakes .15. Cleaned the carb, got new gas, new spark plug, new yamaha cam chain so everything is ready to start.

So I tryed firing her up, but after a few kicks nothing, I had the choke pulled so now I tryed to prime her with one full throttle opening.

Then bang, she backfired, I was thinking she has to start now, so I kicked again and still she backfired, now my guess was the timing is wrong?

Checked, and the timing was good, had the piston on tdc then I noticed the exhaust cam timing is off slighlty (didnt take any pictures sorry) maybe by half a link on the cam chain, tryed adjusting it but theres no chance of aligning the marks on both the intake and exhaust, so fustrating. I took a look behind and the lobs on the intake camshaft arent pointing up, they are more linear (horizontal) to the head, picture no.1 Btw thats my old cam, I installed it becuase it was in mint condition. Picture no.2 is with the intake cam from the new head.

So now I know the intake cam is no good, but need to verify which one has sliped the gear on the shaft?

Did some rough measurements, so you can see the difference.

 

Any help would be appreciated, thanks.

 

 

Attached Thumbnails

  • Old Intake cam.jpg
  • New Intake cam.jpg
  • Old intake vs new.jpg


  • whyzee426F

Posted September 30, 2013 - 04:31 PM

#2

Hi guys, I'm kinda new here, been lurkin around a lot reading before I had to ask for advice.

So I've been rebuilding my yz426f 2001 from bottom up. I guess it skipped a toothe or dropped a valve and the piston slamed on the valves, choping some of them completely off.

I bought a used 02' head which included everything, Ti valves, springs, camshafts etc.

Did the bottom end, bought new piston and rings, installed everything. Checked the clearances, the exhausts are .25 and the intakes .15. Cleaned the carb, got new gas, new spark plug, new yamaha cam chain so everything is ready to start.

So I tryed firing her up, but after a few kicks nothing, I had the choke pulled so now I tryed to prime her with one full throttle opening.

Then bang, she backfired, I was thinking she has to start now, so I kicked again and still she backfired, now my guess was the timing is wrong?

Checked, and the timing was good, had the piston on tdc then I noticed the exhaust cam timing is off slighlty (didnt take any pictures sorry) maybe by half a link on the cam chain, tryed adjusting it but theres no chance of aligning the marks on both the intake and exhaust, so fustrating. I took a look behind and the lobs on the intake camshaft arent pointing up, they are more linear (horizontal) to the head, picture no.1 Btw thats my old cam, I installed it becuase it was in mint condition. Picture no.2 is with the intake cam from the new head.

So now I know the intake cam is no good, but need to verify which one has sliped the gear on the shaft?

Did some rough measurements, so you can see the difference.

 

Any help would be appreciated, thanks.

When I put my motor back together after a complete rebuild, I followed the manual.  I recall the cams needed to be completely horizontal, but it appears yours are both slightly canted up and not level.  Also, I'm not sure what you mean by saying you now know the intake cam is no good.  Why?  Are there no timing marks on the sprockets of either cam that help in alignment?  I thought there were on mine (I used a hotcam for the exhaust to eliminate the decompression lever).  Take your time, relook and rethink, and remeasure and I think you'll get it.



  • 3d0

Posted October 01, 2013 - 01:03 AM

#3

I have intake and exhaust cams from the old head, and from the new head. Thats 2x intakes, and 2x exhaust cams. I used the old intake cam from the head that blow up, it was in perfect condition so I installed it.

If you take a look at the pictures you can see the intake cams (from the old and new head) have the lobes pointing at different angles, thats with the marks aligned with the cylinder head surface.

I'm going to buy her the hotcam AD cam if she fires up, just want to make sure if thats the correct angle the lobes should be pointing before trying again?

Thanks



  • whyzee426F

Posted October 01, 2013 - 10:01 AM

#4

I have intake and exhaust cams from the old head, and from the new head. Thats 2x intakes, and 2x exhaust cams. I used the old intake cam from the head that blow up, it was in perfect condition so I installed it.

If you take a look at the pictures you can see the intake cams (from the old and new head) have the lobes pointing at different angles, thats with the marks aligned with the cylinder head surface.

I'm going to buy her the hotcam AD cam if she fires up, just want to make sure if thats the correct angle the lobes should be pointing before trying again?

Thanks

Okay, so it sounds like you have properly aligned the cams, assuming you're following a manual and aligning with timing marks per instructions.  Is the crank also in the correct position?  If so, you should be there.  You can always torque stuff down then spin the motor by hand with no spark plug.  A few complete cycles of the motor will help to ensure it all lines up without issues.   



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  • 3d0

Posted October 01, 2013 - 10:44 AM

#5

Yep following the manual, the piston is on tdc. I bought new SS valves, so the head might need some work to be done on before I try the new intake cam that has a different angle on the lobes then the old one.

Need to wait two weeks before I can try again! :banghead:



  • jsmith4816

Posted October 02, 2013 - 11:20 PM

#6

What year is your 426? I believe the 01 came with titanium valves and 02 and up had stainless steel. The clearances are different between the two. Check out my thread in this section. It will explain more

Edited by jsmith4816, October 02, 2013 - 11:22 PM.


  • 3d0

Posted October 03, 2013 - 08:00 AM

#7

01 and 02 had Ti valves, SS are less expensive.  :rolleyes:

Mine is a 01, will get all the parts next week so I'll let you know if she starts.

 

BTW did you get your bike to start?


Edited by 3d0, October 03, 2013 - 08:02 AM.


  • jsmith4816

Posted October 03, 2013 - 09:27 AM

#8

No, after a few rides my clearances shrunk so I think they need to be reseated. Doesn't help I am a few hours away from my bike otherwise I would work on it daily





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