> Hoping not to start another firestorm, but I have a very basic question.
>
> My TR3 Service manual says "Turn the engine over by hand until the
> valves of any cylinder are on the "point of rock". Is this the same
> as Top Dead Center?
Well, not quite, but close.
> ... I am under the impression that at TDC both
> valves are closed, and that is what is desired for adjusting the
> valves.
The "point of rock" they are talking about is when a pair of valves (intake
and exhaust for one cylinder) is open by the same amount. If the cam timing
is perfect (which is rarely is), then the associated piston will be at TDC.
Since this is a 4-stroke engine with an even number of even-fire cylinders;
the cylinder opposite in the firing sequence will also be at TDC, with both
valves fully closed. This is a good place to set the valve lash.
Note that with cylinders 2 or 3 "on rock", the TDC marks on the crankshaft
will not be lined up, since they are for cylinders 1 & 4.
There has been some discussion in the past about the fact the cam lobe is
not pointing directly away from the lifter at this point ... some
aftermarket cams are apparently mis-cut so the lash varies a bit depending
on just where you measure it. It's not clear to me just where the lash
should be measured on such a (defective) cam. But since it's the factory
procedure, I always set my valves with the "on rock" method. I find it
easier, especially since you only have to position the engine 4 times,
rather than 8 with the "rule of 9" method given in the Haynes manual.
Randall
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