How Do I Check the Lobe Dimensions on MK2 Camshaft

When I measure the lift on the cam I measure from the outside of the base circle to the nose of the cam and measure the base circle from side to side and subtract the size of the base circle from the first measurement. If the lift is slightly less than expected I don't worry too much, because with less lift there is less likelihood of chucking a valve down the hole through over-revving. If the cam TIMINGS are altered through wear, that is a different story. I suggest it is a mistake to increase the lift on a cam while moving the power band upwards to get more go.

acotrel said:

When I measure the lift on the cam I measure from the outside of the base circle to the nose of the cam and measure the base circle from side to side and subtract the size of the base circle from the first measurement. If the lift is slightly less than expected I don't worry too much, because with less lift there is less likelihood of chucking a valve down the hole through over-revving. If the cam TIMINGS are altered through wear, that is a different story. I suggest it is a mistake to increase the lift on a cam while moving the power band upwards to get more go.

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Very reasonable and common sense comments. I didn't think to measure across the base circle of the lobes (if that makes sense), I just measured from the outside of the base circle to the lobe nose and compared the four measurements to each other. All were the same except for one which was a thou higher than the other three.

I've just measured my original cam which is probably the one fitted in 1970. The base circle is 0.90" and the overall height of all four lobes is 1.220" give or take a couple of thou. (0.320" lift)

Glad you were able to make sense of it. A lot of guys work very hard to get their cam timings to the recommended values. It is not really that important. In the end, if you want best performance, the timings change to suit the exhaust and inlet tracts. So you need the vernier cam sprocket and a lot of patience and a means of assessing performance when the bike is used in anger on various circuits etc. I did a very bad thing when I built my 850 motor. I gave my worn cam to our local cam guru and said 'just give me your best Norton grind', in the belief that whatever it was I could accommodate it When I measured it, it was not much different to a standard 850 cam. I set it up using my previous experience with 2 into 1 exhaust systems and gave it 12 degrees more advance than standard. The motor pulls like a train and will spin up rapidly right through the top of the usable rev-range with the CR gearbox, regardless of what overall gearing it pulls. The problem is the bike is too loud, and I cannot keep paint on the exhaust system, but on methanol fuel, it is excellent.

Very interesting Acrotel. It is flat down where you come from though from memory.

Though I might spot check again!
Well spot checked -sort of
If you check out the profiles (over 20) on my webpage, you will see only about 2 profiles that measuring at 180deg of the cam base circle where you are NOT on the ramps and are really on the base circle. like:
http://atlanticgreen.com/images/cam100.gif

Even the whimpy 88cam you will measure a bit of the ramp (not base circle).

Please disregard the few that were from the beginning and were not re accomplished due to the cam no longer being available to me.The ramps were not completely properly measured in the beginning of my data taking.

http://atlanticgreen.com/camsurvey.htm

That is interesting, I will have a look at it. The only time I've measure the lift of a cam is when I've suspected it was stuffed. And usually I use a dial micrometer on the end of a pushrod while it is in the motor.

acotrel said:

That is interesting, I will have a look at it. The only time I've measure the lift of a cam is when I've suspected it was stuffed. And usually I use a dial micrometer on the end of a pushrod while it is in the motor.

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Doing a profile in an engine is quite laborious. Hence the rig I made which will yield the same results as if the cam was in an engine. Having made a second "shoe" with a 3" radius I can swap them out and do early cams or later hot rod cam requiring 3" radiused lifters.
The worst accuracy device is the visually reading and manually setting the degree wheel by viewing the pointer.
Not much more than 15 seconds to swap the cam out, and a minute to set up the degree wheel.

That's way cool, Dave!

The worst accuracy device is the visually reading and manually setting the degree wheel by viewing the pointer.
Would it help to have a much larger degree wheel?

How do you correlate the measurements you get off your test rig, to performance aspects you get when the cam is in a motor which is operating with the exhaust system attached ? Do you try different amounts of cam retard and advance ? And what is your major objective - mid-range or top-end power ? If I did that, I would probably just set the cam up to something I thought looked good. - A bit of judgement, but more of a guess.