Cam Timing

[ribbert]

Hi Guys,

I have a '93 FJ with 57k's on  it that I managed to "cook" in heavy traffic and 40c + temp. I am reassembling it after a re-bore and new pistons and having problems with the cam timing.  I assembled and timed it according to the sequence described in the manual ( many times! )
While I have no problem timing the ex. cam to the crankshaft, the in. cam always ends up ahead or behind the timing mark - being the punch mark on the cam sprocket.  I have rotated the in. cam back and forth one tooth while keeping the tension on the chain many times to no avail.
Any suggestions would be much appreciated.

Regards
Ribbert

[racerrad8]

The chain is dropping off of the crank on the intake side when you are installing the cam. You need to keep the rear chain guide against the chain with slight pressure which will hold the chain on the crank teeth.
Secondly, you have to allow for the rearward rotation of the cam as you tightening the cam caps.

It is difficult for most, and there is no real "easy" way to do it.

Randy - RPM

[fj1289]

Some additional comments from an amateur:

... You need to keep the rear chain guide against the chain with slight pressure which will hold the chain on the crank teeth.

Fairly easy to do this by pushing on the chain guide with your finger through the hole where the tensioner mounts - a little awkward to tighten the caps single handed, but that's the best way I've figured out so far...

Secondly, you have to allow for the rearward rotation of the cam as you tightening the cam caps.

Took me a LONG time to figure out that one!  Set the cam just so, snug everything down, and it would end up all out of whack!  Finally paid attention to the cam during the process, SAW it move and the light bulb came on!

Also, if you have adjustable sprockets or you slot your stock ones, you can "cheat" a bit, but you have to actually degree the cams (using a degree wheel and dial indicator).  When I degree the cams, I'll get the crank in the right position (via the degree wheel), loosen the sprocket bolts, and use a wrench to turn the cam to a appropriate position (according to the dial indicator) and snug down the sprocket bolts.  A lot quicker than the old adjust the sprocket, check the timing, tweak the sprocket again, check again, tweak, check, tweak ... etc.   

Chris

[ribbert]

Thanks for the suggestions, but I still have the same problem.  Allowing for the rollback of the cam and keeping the chain tight I had figured out on some earlier attempt but still end up "half" a tooth -or about 5mm- above or below level with the top of head, and the hole viewed through no. 3 bearing cap similarly forward or aft of centre. Keeping everything tight, and marking the chain and sprocket, I have moved the cam 1 tooth only, left and right, and the mark moves from just below to just above level with head surface by the same amount.
This motor has been apart very early in its life (can't imagine why) it has workshop job no. etched onto the major bits (crankcase halves, barrels etc.)  If undue force was applied while assembling could the cam chain have been stretched and would it have this effect?

ribbert
Melbourne, Australia

[VMS]

Hi Guys,

I have a '93 FJ with 57k's on  it that I managed to "cook" in heavy traffic and 40c + temp. I am reassembling it after a re-bore and new pistons and having problems with the cam timing.  I assembled and timed it according to the sequence described in the manual ( many times! )
While I have no problem timing the ex. cam to the crankshaft, the in. cam always ends up ahead or behind the timing mark - being the punch mark on the cam sprocket.  I have rotated the in. cam back and forth one tooth while keeping the tension on the chain many times to no avail.
Any suggestions would be much appreciated.

Regards
Ribbert

Slot the cam gears

[Harvy]

This motor has been apart very early in its life (can't imagine why) it has workshop job no. etched onto the major bits (crankcase halves, barrels etc.)  If undue force was applied while assembling could the cam chain have been stretched and would it have this effect?

ribbert
Melbourne, Australia

Ribbert........you say its been apart b4.......... are the cam sprockets slotted by any chance?

Harvy

[Harvy]

Slot the cam gears

Sorry Jim, I missed your reply.........was just thinking maybe they already are?

Harvy

[ribbert]

Slot the cam gears

Thanks Jim and Harvy, no, it doesn't have slotted cams and while I have read much (good and bad) about playing around with valve timing it shouldn't be necessary to reassemble a standard motor, unless of course this was a known common problem, which it's not.

Ribbert

[TRoy]

While I have no problem timing the ex. cam to the crankshaft, the in. cam always ends up ahead or behind the timing mark - being the punch mark on the cam sprocket.

BTDT, forget about the dots on the cam gear you may never get them "perfect"...  use the dots on the cams which line up with a hole thats made into 2 of the cam caps. I forget which cam caps have the hole in 'em, use a bright flashlight look down thru the hole in the cam caps you should see the divets/dots in the camshaft. may need to blow it out to see.

[andyb]

^ We have the winner..

[VMS]

I think there is a hole in the #3 cam cap?
At TDC the two dimples should be centered in the hole on both cams

[andyb]

Or as near as you can swing it.  Should be no more than a half tooth off, but that's still a significant (what'd we work out in the other thread, 8.5deg or so?  Something horrible like that).

Last I had my head off, with slotted sprockets, I just aligned the little dots through the cam caps and the bike ran very well afterwards (better than it had before, more top end).  Slotted gears are $50 or so if you buy them premade, and let you get the spec timing correct.  You could also move things around if you wanted a bit more midrange (or top, or bottom, or..)

[VMS]

If you can't get it where you want it and want to go the slotted cam gear route, just let me know.
Jim
www.vmsmotorsports.com

[fj1289]

Are you reusing the camchain with 57K on it?  If so, you will probably have to have slotted gears to get the timing back to stock!

[VMS]

I hope not...that thought never entered my mind, I assumed everyone replaced the starter and cam chains whenever the case is split

Good point