> Michael, I'm not sure what your source of confusion is, except perhaps
> you still can't read the original question, which was "what is the best
> way to set valve clearances, hot or cold?" For the third time (by me)
> the answer is hot.
How 'bout explaining _why_ you think that, Nolan ?
> It's roughly akin to the question "which is better, an oil pressure
> gauge or idiot light?" The answer is a gauge.
Not if one has no clue as to what the correct reading for the gauge is ...
> However, the hot spec for valve lash would be about 2 thou tighter then
> the cold spec.
But if the hot spec can be predicted from the cold spec, why is measuring it
hot any better ?
> This is due to thermal expansion of the valve,
> particularly the exhaust. A little more for the exhaust, a little less
> for the intake.
But, the temperature of a 'hot' exhaust valve varies greatly depending on
how recently the engine was run, and what EGT it was running at the time.
How long does it take for the exhaust valve to reach equilibrium with the
rest of the head (and the intake valve) ?
> You can determine this readily enough with a basic
> engineering handbook covering material properties, of which engine
> valves are made of. Before you point at the pushrods, they will expand
> almost identically to the bock and head due to their similar material
> and operating temperatures.
Except that they aren't similar materials (typically steel alloy vs cast
iron), and certainly aren't necessarily the same temperature, since the
block and head are involved in carrying heat away from the cylinder, while
the pushrods are not. Then of course, there's the added complication that
some Triumphs don't have pushrods ...
Oh, and what about the aluminum rocker shaft pedestals ? Do they also
expand at the same rate as the pushrods ??
> If that is not sufficient for you, examine
> various manuals for the many engines that give hot and cold valve lash
> (there are quite a few btw). For example the very common R series
> Toyota engine gives both hot and cold lash specifications, about 2 thou
> apart. Procedures recommended are for hot adjust btw. Still not good
> enough for you? In the late 80's early 90's Honda motorcycles went to a
> zero hot lash on their motorcycles, with a 2 thou cold spec clearance.
But are any of these engines identical to Triumph engines in terms of
materials used, pushrod & valve lengths, cam grinds, etc. ?
> Your worries that people will destroy their engine should they set the
> valve hot to a cold clearance is unfounded, especially if you stop to
> think about it for a second. The worse that will happen is they will
> get a little bit more clatter out of the valve train, nothing more.
> They would simply be running about 2 thou excessive clearance. Even if
> a person were to get seriously confused by all this and set the valves
> cold to a hot spec (2 thou tighter), with the huge lash clearances
> already given by Triumph they would merely have a bit less valve train
> clatter then the typical Spitfire. There is no inherent danger of
> burning up valves in a Spitfire by setting the valves either hot or
> cold.
So now it doesn't matter if you're a few thou too tight, or a few thou too
loose ?
Seems to me the main advantage of setting valves hot is having something to
argue about ... and burning your fingers.
Randall
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