[DeTomaso] Pantera fall down go boom :<(

[B. Seib]

Random thoughts on gear drives:

I think the real destructive forces in the valve train drive are related to
harmonics (as in: vibrations in transmission of driving force).

Gear drives transmit these destructive harmonics much better than chains or
belts, which absorb some of the bad vibes.

Bad harmonics are not always present at all rpm, but when they are, they can
be very destructive.

I would imagine harmonics are pretty much a constant threat in a camshaft
with the varying loads that involves and the crankshaft has it's own share
of harmonics (thus the damper). If the harmonics of the driving crankshaft
and the driven camshaft have a major argument and the gears don't absorb any
of it, there will be broken things sooner than later. These harmonics will
change at different RPM and every change in cam design, stroke, rod length,
etc. If this severe conflict of harmonics never occurs, we'll never need to
know about them. If they are being transmitted through a marginal gear to a
heavily loaded oil pump, all bets are off.

A rev limiter must have the potential to mess with the harmonics present in
these systems.

Heavy duty truck engines and some marine engines used gear drive to cams
years ago. They were able to run for much longer mileages/duty cycles than
any cam chains could. I don't know if that is still the case. I don't think
high RPM or heavy valve springs was in the mix. I vaguely recall a gear
driven L88 Corvette cam in 1968, but I'm not sure how successful it was.

Many very successful high RPM motorcycle engine use gear drive to cams, but
the ones I've seen up close have elaborate shock absorbers in the gear hubs
if I recall correctly. I thought they were for noise control, but perhaps
they also absorb harmonics? I do recall a dealer having to replace all the
drive gears on warranty for a VF1000R because these items failed.

More intelligent comments are invited from mechanical engineers (and
everyone else too). It's an interesting subject.

Barry