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. The question was *not* "what are the hot
clearences?", or "how do I set lash" or anything else. Just "what is
the best way to set valve clearances, hot or cold?"
It's roughly akin to the question "which is better, an oil pressure
gauge or idiot light?" The answer is a gauge. This would not suddenly
equate to knowledge of hidden oil pressure gauges on Spitfires, or
secret pages in the repair manuals describing how to uncover them. Just
an answer to the question asked.
However, the hot spec for valve lash would be about 2 thou tighter then
the cold spec. This is due to thermal expansion of the valve,
particularly the exhaust. A little more for the exhaust, a little less
for the intake. 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. 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.
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.
Lastly, if you're still with me, you can look at the tuning
characteristics available to you via changes in valve lash. It's a very
old trick to use large lash clearances with an overly hot cam to allow
the engine to be more streetable, while cranking the lash back down to
go racing. In fact, companies like Crane and such use exactly that
technique on several of their hydraulic lifter series packages with that
controlled leakdown. The hydraulic lifters do not pump up fully until
around 3,000 rpm or so, leaving the wild lump stick detuned below that
rpm range, and then bringing in the overlap and such when the engine is
reved up. Works nicely btw, my father happens to have one of those
setups in his 302 Mustang.
Now, if my providing you all the above information makes me, as you
describe a "junkyard mechanic and untrained amateur engineer", so be it.
I'll disagree, but you're certainly entitled to your opinion.
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