When a camshaft is reground, they do remove material. However, they make
sure that the base circle (the part of the cam where the valve is closed)
is reduced such that it leaves the lift the same. So when you measured a
"lobe height" .06 lower for the new cam, you wer really measuring that the
regrinder had taken .03 off everywhere since you were capturing the
reduction of the lobe height and the base circle. As another post
mentioned, the best way is to measure the base circle perpendicular from
the lobe, subtract that dimension from the measurment over the lobe, and
compare the differences.
There is a tolerance for cam shaft dimensions. In fact, there is quite a
business for "blueprinted" camshafts. These are camshafts that are
precision reground to the maximum lift and duration specifications listed
by the manufacturers. Blueprinted camshafts are one of the speed secrets
for racing classes that require a stock camshaft. I don't know how much
slop MG allowed but a blueprinted cam in a 60's american car can really
wake it up.
Regards
Bill Eastman
61 MGA
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