My comments are in line with Greg Solow's. My principal concern is with
the shaft diameter as it relates to the stiffness of the valve train,
but it could also be related to breakage. Ideally, you want the valve
train to be stiff to reduce the deflection and vibrations. I found the
same article that Greg mentioned in the Brooklands reprints (for TR2 &
3) that explained that Triumph beefed up the front portion of the shaft
to increase the stiffness. According to my measurements, you can't get
more than 0.300 lift from a regrind without cutting into the core (the
part between the lobes). If you want 0.370 lift from a regrind, you'll
have to undercut the core about 0.200 inch. That reduce it's stiffness
by more than 50%. If you grind on a new blank and keep it as large as
possible, you will not have to make it as small, so it should be both
stiffer and less likely to break.
British Parts Northwest did carry blanks for a while, but I understand
they no longer plan to stock them. I've just ordered a small batch from
the UK. I've seen problems with both the drive gear and the bearing
surfaces. My TR3 and Tony Drew's TR4 both have been running cams ground
on new blanks without any problems.
Perhaps in this discussion, it would be useful to know the lift of the
cam and whether it was new or reground. You'd expect the front portion
of the cam to be the part most likely to break.
Larry
Bob Kramer wrote:
> Bob,
>
> Larry Young, who is designing camshafts for some of the FOT, likes to
> use new blanks rather than regrind for his race camshafts. His
> thinking is that during the regrind they also reduce the diamter of
> the shaft to keep it smaller than the base of the lobes. He is worried
> about your exact problem. Maybe he'll chime in.
>
> Bob K
> Austin TX
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