Cam timing tolerance?

[cstreit]

So my cams specify a 5.2mm lift at 360 degree rotation, (or .205").

What is the acceptable variance? '

I can't seem to get closer than about .05mm off (or 2 thousandths inches).

[ChrisBennet]

What do you mean by variance? Do you mean the difference from the spec mid point or the difference between left and right cams? Sorry if I'm being a little dense.
-Chris

[cstreit]

Both.

[ChrisBennet]

Chris,
Even if this isn' much help, maybe it will bump it up so one of the experts will see it.
The same source you used for the "measurement value" (or whatever they call it) should have spec'd the tolerance. For a 964 cam it would be spec'd as 1.26 +/- .1mm for example. If your valve to piston clearance is small, the allowable tolerance is probably smaller.
If you want to spend the time (and we already know you are anal about this sort of thing ) you can match left and right almost exactly. The steeper the slope of the cam, the harder it will be of course.

You won't be able to get them any closer than the "noise"/error in your measurements. Say you make the measurement 10 times and the range of measurement varies by 0.02mm for the left cam and you do the same thing for the right cam and the range of measurement is 0.03mm. In this example, you won't be able to match the left and right cams any closer than 0.05mm. At least that is how I would figure it. Not that I'm that obsessive...
Hopefully someone smart can explain it better (or correctly).
-Chris (the other, slower one)

[RoninLB]

the chain and teeth don't return to exact same match every turn.. so a variance in that system happens.. I believe it takes 9 revolutions to return the teeth and chain.. easy to test my probable number of turns w/some paint on tooth and link.. this issue had me spinning, anally talking, LOL