Camshaft Timing - At What Lift?

[Anthony]

Could anybody tell me what lift the Triumph camshafts are measured at?

 

i.e. if the timing is 35-65, is that at 0.050" valve lift?, or is some other measurement used?

 

I have an unidentified camshaft that I'm trying to work out the specs of, but don't have an original one to compare it against.

 

Thanks.

 

[That Man]

It's when the valve either starts to open or finishes closing with standard valve clearances.

If measuring the camshaft directly it gets tricky as you'd need to calculate what the valve clearance would be at the follower, this would be very important as the quietening ramps are very shallow and would give a big variation in the angles you'd measure. Also remember it crankshaft degrees not camshaft degrees.

 

[Anthony]

I'm rebuilding an engine at the moment, so my plan was to measure the camshaft during installation.

i.e. Set the valve clearance to zero, rotate the crank until the valve is lifted by XXX thou, and then read the degrees of rotation off the timing wheel.

I just don't know what Triumph and the current camshaft vendors (Newman, Piper, Kent, TT, etc.) use for their lift figures.

 

[That Man]

If you don't know the specifications of the cam you intend to use it does make it very difficult to set it correctly.

If you are sure it's a original Triumph factory cam it will be symmetrical so you would use the method described in the workshop manual for camshaft alignment

If it's a after market cam it should be marked by the manufacturer as to which profile it has.

[PeteStupps]

Hi Anthony,

There was a detailed discussion about this subject on the Sideways forum a while ago - http://sideways-technologies.co.uk/forums/index.php?/topic/8106-how-to-measure-a-cam-in-the-hand/#comments

Apparently there is no definite answer to your first question. Americans use 0.0050" but Triumph (and other British car makers) did not. They might have used 0.010" but it's a bit complicated...

Pete