Dick:
I went back and took another look, and I overstated the resolution
of this method, but the idea remains the same. I also mis-stated the source,
it was actually noted in "Tuning Standard Triumphs over 1300cc". It is
the Vizard book that is available on line at
http://www.141.com/triumphs/vizard.pdf
Let's say, for the sake of argument, that the cam sprocket has
36 teeth, or one tooth every 10 degrees. Obviously, moving the cam
sprocket one tooth will advance or retard the cam 10 degrees.
If turning the cam sprocket over effectively moves the sprocket
1/2 tooth, we now can change the cam timing in 5 degree increments.
Lastly, recall that the cam is rotating at 1/2 the crankshaft
speed. We divide everything by 2, and we end up with a resolution of
2.5 crank degrees for the cam timing. This means that with the stock cam
sprocket, we can get the cam timing within 1.25 degrees of nominal
assuming a worst case scenario.
Vizard recommends that in the event the ideal cam timing
falls right on this 1.25 degree increment, that the cam be installed
1.25 degrees retarded, as this will boost top end power slightly.
For street or even auto crossing this is good enough. If you
are a serious racer, you want it to be perfect, so you would do as
you suggested and with some machine work you could get the timing
spot on.
See Shane Ingate's cam page for a discussion of the effects
of retarding or advancing cam timing.
Cheers,
Vance
------------------------------
1974 Mimosa Yellow Triumph TR6
Cogito Ergo Zoom
(I think, therefore I go fast)
-----Original Message-----
From: tr6taylor@webtv.net [mailto:tr6taylor@webtv.net]
Sent: Friday, October 04, 2002 11:49 PM
To: vance.navarrette@intel.com
Cc: 6pack@autox.team.net
Subject: RE: Adjustable camshaft
Vance---I've never tried this myself, and am in no position to doubt Mr.
Vizard. It is written that one can "turn over the cam sprocket" and
there will be a timing difference of "one or two degrees." (Kastner) I
can visualize this, but don't see how one could then move to different
teeth and come up with combinations. I would think that either the stock
timing location that gives a straight up "0" setting, or the "reversed"
sprocket with it's one or two degrees of offset are the only choices
here.
It could also be that I am not following the proposed line of thought
that is suggested by Vizard.
Other options would be elongating the cam sprocket bolt holes, eccentric
bushings, or making an off-set key for the crank. One then would need
access to a dyno to know if power improvements are being made.
Still, you made a good point in bringing up this possibility, should one
find that doing the sprocket reversal gets one closer to whatever is
carded as correct for the cam.
Thanks,
Dick
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