Topic: Can't get timing marks to line up...Stretched cam chain?

[justinmcgiver]

Ok, when the cam is turned so the two marks on the end are lined up with the seams of the end cap and the key groove is pointing up(as per the manual) the "T" mark is not lining up perfectly. The "T' mark moves about .050" too far when the cam is turned to where it needs to be. I have tried walking the chain in both directions, and turned the sprocket 180deg on the cam and this seems to be the closest I can get it. Should these marks line up exactly, or is there some tolerance that can be accounted for later when doing the timing? Or am I doing something wrong? 
Thanks

[heffay]

at the same time as adjusting the timing you'll need to adjust the points gap... sometimes it takes several adjustments back and forth between the two to get them both right.  so yes, that tolerance you're asking about is probably the gaps not allowing you to adjust the timing correctly.

are you working from a manual?

[Bodi]

If the crank is a bit past the T mark with the cam lines level to the head it could be a stretched cam chain or worn slider (what model?). But the cam marks are not perfectly exact, they are really only there so you get the chain on the right tooth. Only way to really tell is to degree the cam. The engine will run OK as is though, you need to be pretty far off to cause piston/valve interference.

[bryanj]

As Bodi said, the only time the marks line up exactly is when everything is new (and then it aint 100%)

[justinmcgiver]

Thanks for the replies,
I will button her up now as is.
Yes I am working from a manual but not actually timing, just getting the crank lined up to the cam(static timing?)
Also I have a new dyna s ignition so I am assuming the points gap will no longer affect my timing as heffay was saying.

[kettlesd]

As Bodi said, the only time the marks line up exactly is when everything is new (and then it aint 100%)

True enough. You want to find exact TDC,  then insert a long dowel through your spark plug hole and rotate engine very slowly while watching the dowel oscillate with piston travel. Stop when the dowel is at its highest (TDC). Pretty much guarantee that it wont match your mark exactly.

[JohnG]

The best you can ever get on the cam timing is to within 1/2 tooth with stock parts, even new. If you want it better than that, you need to "slot" the holes in the sprocket so you can rotate the cam a little relative to the sprocket.  Once you have things perfect, put Loctite on the bolts and tighten them up according to the shop manuals torque spec.  If you want to go beyond this, get a degree wheel and dial indicator.

Slotting the sprocket only takes a few minutes and thereafter guarantees quick and more accurate results.

        John
        1976 CB750F

[justinmcgiver]

Other than a Bridgeport with a rotary table, what method would you use to slot the cam sprocket?

[JohnG]

I put a round file in a drill press and just held the sprocket in my hands until I was happy. Basically I went about half the width of the bolt each way but you might get away with less than that depending on how far off you are. No point in overdoing it.

[kettlesd]

Bringing the camsprocket to any machine shop is an easy and inexpensive way to do it. Not to say it hasn't worked well for him, but using John's idea of the file chucked in a press I'd be concerned about radial runout - meaning deviating from the imaginary circle that the mounting holes are drilled into, that runs concentric to the center of the camshaft . Even a small bit would make the sprocket spin out of true (like a washing machine with a load out of balance) - setting up nasty vibrations and stresses in the cam/camchain/valvetrain/etc.etc.

[JohnG]

I thought of that but there is a hub on the cam that maintains the concentricity so all the bolts are doing is keeping it from rotating one way or the other.  In any event if you can get it done precisely in a machine shop, by all mean go for it!!

              John