Need help with timing issue


8 replies to this topic
  • rg_series

Posted March 20, 2006 - 06:35 AM

#1

My 89 XR600 has been down for two years now and I am ready to go riding again. I tore everything down a while back and had the cylinder bored, new piston, new rocker arms, 3 angle valve job, new stainless valves, new barnum's grind cam. My problem is, when I installed the cam, I lined the lines on the sprocket up parallel with the top of the cylinder head when the T mark on the rotor was lined up the notch on the side case. The problem is that the piston is not at top dead center when the rotor says it should be. When the piston is at TDC, the II mark shows up through the viewing window instead of the I T . What did I do wrong? Don't know if it matters, but the previous owner installed a niks pro-x rod.

  • rg_series

Posted March 21, 2006 - 04:51 PM

#2

^^^^^

  • Thumpmeister

Posted March 22, 2006 - 12:04 AM

#3

I think some Hondas are just like this...

I just finished a rebuild on an 84 XR 250. Granted, its not the same engine, obviously, but a lot of the pricipals are still the same. Anyway, when I went to do my timing, I had a similar issue. I would get the "T" mark right in the middle of the hole, and go to set my cam. The only problem was, was that the cam was about a half tooth off. When I would go to set the upper cam gear, the lines wouldn't be exactly parallel with the top of the head. Seemed kind of wierd, but it was the only thing I could do. Turns out this is normal, and you just have to get it to be the closest tooth you can get.

This was on a completely OEM rebuild, so it might be a bit different on your ride. But, I just thought I would say that since I just went through a similar issue.

  • creeky

Posted March 22, 2006 - 05:13 AM

#4

I have had the same experience as Thumpmeister on older XRs, I ran them anyway even though the sprocket timing marks were slightly off. XRs Only used to sell a cam sprocket with slotted bolt holes to allow cam timing to be fine tuned, don't know if they still offer it or not.

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  • rg_series

Posted March 22, 2006 - 07:36 PM

#5

Thanks for the responses, although I am very comfortable with my cam timing. The problem is that the piston is only mid way up it's stroke when the rotor T mark is lined up with the notch in the side cover.

  • creeky

Posted March 23, 2006 - 05:02 AM

#6

Sounds like the flywheel is not fitted correctly or maybe wrong flywheel???

  • Motosprtman

Posted March 23, 2006 - 11:55 AM

#7

I think you may have answered your own ?

"Don't know if it matters, but the previous owner installed a niks pro-x rod."

If this rod is longer i.e. a "stroker" then TDC will obviously change and the makrs on the flywheel become irrelevant to the actual position of TDC acquired via the istallation of the new rod. Bring the piston to known TDC and then set your cam timing.

  • creeky

Posted March 23, 2006 - 12:55 PM

#8

I



If this rod is longer i.e. a "stroker" then TDC will obviously change and the makrs on the flywheel become irrelevant to the actual position of TDC acquired via the istallation of the new rod. .


Am I missing something? I always thought that the length of the connecting rod has nothing to do with TDC, TDC is when the crankshaft throw has reached its' uppermost point in its' rotation. The position of the flywheel on the crank should be such so that the TDC marks are aligned when the crank is in this position. Help me out here.

  • rg_series

Posted March 25, 2006 - 10:54 AM

#9

creeky I think you are correct but regardless, niks doesn't make a stroker rod for an xr600, it is an oe replacement.





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