Message text written by "Randall Young"
>Got to thinking (always a dangerous process)
Always gets me into trouble. ;-)
>about _why_ Triumph might have
>switched to a bolt-on ring gear on the later TRactor motors. AFAIK none
of
>the other motors used a bolt-on ring gear, and early flywheels are not
known
>for being troublesome, so why the switch ? I'm guessing that it had to
>change, because they wanted to replace the troublesome early starter and
the
>drive gear on the later starter was bigger. Given a choice of moving the
>starter mounting points in the block casting, or making a different
>flywheel, obviously the flywheel gets the change.
Why not just change the gear on the starter? But back to your point, true,
changing the flywheel only requires a simple programming change in the NC
mill.
What? Oh. Nevermind. How about a change in the mill set-up.
>But why bolt-on ? Could it be they were worried about stocking spares for
>earlier cars, and planned to offer a bolt-on ring gear that would allow
the
>later flywheel to be used with the early starter ?? Has anyone ever heard
>or seen such a thing ?
Since these parts generally come from the saloon of similar vintage did
they use the same setup there? Or perhaps the Vangard line was
discontinued and the contemporary saloons all used variations of the SC
engine. (Just a guess) If so then the R&D budget to prove out a press-on
ring gear wasn't there and the safe bet is to bolt it on.
>Also, we all know that the later flywheel was heavier by about 7 pounds,
but
>how did it's rotational moment of inertia (which after all is what matters
>in a flywheel) compare ? It was presumably a smaller outside diameter
>(can't go check at the moment) because the ring gear was both smaller
>outside diameter (to suit the larger starter pinion) and wider to leave
room
>for the bolts. Thus, the Triumph engineers may have added weight to keep
>the same moment of inertia.
But the heavier ring gear will contribute to the angular inertia partially
compensating for the smaller diameter flywheel. If inertia is I = MV then
angular inertia is Ia = MwR (where M= mass, w is angular speed in radians
per second (Omega) and R=radius) if R is reduced then M can be increased to
comensate and yeild the same result.
>Factoids, comments, opinions ? Even brickbats are OK, as long as your aim
>is lousy <G>
Opinion: speculating why the factory did something to a limited production
sports car without considering the state of the saloon cars from which the
majority of the parts came is missing an important part of the picture.
Perhaps JonMac can pur a little historical (and hysterical) context around
this issue.
Cheers
Dave
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