>> I just receiced my new (reground) cam from (nameless for now) and after
>>measuring it I find the lobe sizes to be different accross exhaust lobes by
>>as much as .020. Same with intake lobes.
>>Is this normal?
>>Whats the best way to measure cam lobes?
How did you mesaure it. With a caliper or a Micrometer? Don't worry yet. The
only way to accurately measure a cam aside from some very expensive equipement
is to use a dial indicator with the cam in a block (or similar jig.). What you
are trying to measure is the relative difference in distance from the
centerpoint of the cam. Since a lobe that is more eccentric will require
less height (from centerline and across the lobe) to achieve the same
difference it is not a given that your cam is bad. However you must then
question whether the ramping and other parts of the profile are correct.
A cam in a car usually has as great a difference in the small side of the lobe
as the big side. This is because you are limited in the height of the lobe by
the cam bearing journal size, so the only way to increase lift (after a point)
is to increase eccentricity by removing material from the small side. Some of
the best information I have read about valve trains comes from the Mopar Engine
book (yes I am a closet Wedge head, well closet only as far as the TR list).
Good discussions on theory and practice. Not all applicable to LBC's.
As becomes clear from good sources such as this cam choice is absolutely
crucial. You can match (carb to cam, valve sizes etc) everything carefully and
still have a subpar engine with a bad cam. With something as involved and
critical as cam choice I would check with an expert like Ken Gillanders of
British Frame and Engine.
He likely has dyno data to back up any statements he makes.
I am not saying I an expert on cams, but I do know that this is not a subject
to take lightly, and that things are often not as they seem with cams.
Tom Leake
CTC 50609 L
CTC 50250 L
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