cam chain sprocket question


8 replies to this topic
  • gstt500

Posted February 03, 2008 - 06:19 PM

#1

I'm in the process of reassembling my 2000 xr650L and noticed while bolting the sprocket back on the camshaft that the camshft chain sprocket has another mark in addition to the two marks that line up with the top edge of the head. this is another line that would be 90 degrees from either side mark, if that makes sense. Anyways, I'm thinking that it should'nt matter if this mark goes to the top or bottom as the piston is at tdc but since this machine has the decompression mechanism on the cam shaft it may matter the way that the sprocket is bolted back on the the shaft. Any suggestions?

  • resurrection

Posted February 03, 2008 - 09:26 PM

#2

With single cyl.and cam then at tdc the spocket can go on with no concern.
These marks as the bolts locate sprocket.they will line up with top edge to ref.with crank mark.
Then.
Your biggest concern is no chain slop from sprocket to crank .Rotate and check both marks again,after tensoner is installed
The decomp. is fixed on cam.

  • crmc33

Posted February 04, 2008 - 04:18 AM

#3

As you say, it doesnt matter which way round the sprocket goes, as long as the main lines are inline with the head edge and the cam is either lobes up or lobes down.

Getting finer adjustment of the cam timing means slotting the sprocket holes of course. Ive found that my hotcam was quite retarded with the standard bolt holes, as it also depends on chain slack, head gasket thickness etc. This is due to the head skimming Ive done rather than the hotcam dimensions.

Hope this helps anyway

  • Motosprtman

Posted February 04, 2008 - 11:29 AM

#4

I always assemble cam lobes down - at TDC - and horizontal sprocket line (marks) flush with the surface of the head.

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  • gstt500

Posted February 04, 2008 - 03:18 PM

#5

Thanks for the advice. Just wanted to make sure, followed procedures in my Clymer manual but it's a little vague on some of the 650L stuff. Most of my experience has been with older bikes and this motor seems a bit more hi-tech than what I'm used to, less tolerant of error anyway. Spent most of the weekend reassembling the motor after replacing a worn countershaft, the bike only has 8k mi on it,must be a weak point. I think I'll keep the drive sprocket splines lubed to make sure I don't have to do this repair again.

  • zipper600

Posted February 04, 2008 - 03:35 PM

#6

As you say, it doesnt matter which way round the sprocket goes, as long as the main lines are inline with the head edge and the cam is either lobes up or lobes down.

Getting finer adjustment of the cam timing means slotting the sprocket holes of course. Ive found that my hotcam was quite retarded with the standard bolt holes, as it also depends on chain slack, head gasket thickness etc. This is due to the head skimming Ive done rather than the hotcam dimensions.

Hope this helps anyway



Eheheh.....dude i rode my XR600 for a year without almost no idle but reving like a maniac cause someone skimmed head and i didnt know.I found out cause my bike had more compression than others ive seen and the cam marks never aligned correctly.But i never thought that was the issue so i was letting a bit advanced.Was crazy to ride it that way. Then onde day decided to slot the sprocket holes to give it a try and voila.Found out with the help of Eddie Sisneros from Jetting Forum!!
Thank you Eddie!!!:busted:

  • resurrection

Posted February 04, 2008 - 03:36 PM

#7

I had the same problem the keeper was not offset when bolted on .
I just tack welded keeper in place.

  • crmc33

Posted February 05, 2008 - 04:39 AM

#8

Note that if you skim the head (makes the engine height shorter) it actually retards the cam timing if you use the std sprocket bolt holes. Which can be beneficial for off roading of course!

  • zipper600

Posted February 05, 2008 - 06:38 AM

#9

Note that if you skim the head (makes the engine height shorter) it actually retards the cam timing if you use the std sprocket bolt holes. Which can be beneficial for off roading of course!


i could let it advanced or retarded..i let it advanced..i only use it on road..i was thinking in next rebuilt to use a high comp piston but i never understood how the piston gives more comp.The piston pin-top piston measure is bigger to increase piston height?
If so because the head was skimmed i can not use a high comp piston cause of valve-piston clearance?What do you think?





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