Mike:
The take up clearances are specified by the cam manufacturer,
and depend on the aggressiveness of the "take up" ramp on their cam.
Normally they assume a stock rocker ratio.
The rate of rise at the lobe is constantly changing over the
lobe. The initial ramp is very gentle to take up the lash in the valve
train on a solid lifter cam. After the initial lash is taken up, the
rate of rise will increase rapidly to begin accelerating the valve.
The duration of the take up ramp, and the rate of rise are all
proprietary to a particular cam grinder, and this information is usually
jealously guarded. To make matters worse, there is no standard for
quoting advertised duration, which is supposedly seat to seat timing.
Some measure it at 0.001" lobe lift, some quote it at 0.005" lift, some
at 0.010" lift. This is because measuring the duration at 0.000" lift is
very difficult since the lobe is rising so slowly as the valve begins to
lift off the seat. US cam manufacturers usually quote the duration at
0.050" lift as it is when the valve is effectively open, and it is easy
to measure.
So to answer your question, always use the lash recommended by
the cam manufacturer. You can try to experiment if you wish, but get it
set too tight and you will break something. Stetting it tighter will get
you a tad more lift and a bit more duration, but the likelihood of cam
failure begins to climb at some point.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of DaCRANEz@aol.com
Sent: Friday, March 10, 2006 1:35 PM
To: 6pack@autox.team.net
Subject: valve clearances
Want to get a group opinion on the proper valve lash settings for a
modified
TR. I installed a 150PI cam and Goodparts 1.65to1 roller rockers. TRF
catalog
specifies .015 on intake and .017 on exhaust. This seems a bit loose to
me.
Any feedback welcome
Mike '71 TR6
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