LETTERS TO THE EDITOR
With sophisticated computer-assisted design and engineering, engine
resonance problems are not very
common these days. However, they
do occur. One clue that your problem
is being generated within or by the
engine is the simple fact that it
occurs in neutral as well as in gear.
Vibrations can be caused by “natural
resonance” as well as injection, timing,
and exhaust system design issues.
Take two lead weights, preferably
about 40–50 lb. each, and secure them
together by a length of chain (dive
weights strung together will work).
The chain should be long enough
that the weights can be hung over
the engine athwartships, reaching
about midway down each side of
the engine’s block. Be sure the chain
doesn’t damage or pinch wiring or
plumbing. If the vibration moves up
or down the rpm band with the
weights in place, then it’s very likely
that the engine does have a resonance
“issue,” but that’s not the end of the
story, because this resonance could be
inherent or induced.
In order to rule out the possibility
that you have a malfunctioning
injection pump, have a diesel mechanic
check the injection timing. Then, check
to make sure each injector is working
properly by taking them offline one at
a time as the vibration is occurring.
If the vibration goes away when one
cylinder is offline, there’s a possibility
it is the cause of the vibration, which
could be a result of a malfunctioning
injector or pump. This can be tested.
While the mechanic is aboard, have
him or her check the exhaust back
pressure. If no problems are found in
the injection system and the vibration
problem persists, then a slight re-pitch
of the prop probably would not
cause severe operating problems. If
anything, slight over-revving at wide-open throttle would be preferable to
under-revving, and thus it would be
preferable to reduce rather than
increase pitch. However, I would
prefer that you not leap to that fix,
because it may simply be masking
another problem.—Steve D’Antonio
MANY THANKS, BILL;
ADVICE ON HOME-BUILT CATS
My wife and I want to thank you,
Bill, for the great service you have
provided to the boating world. We
love PMM and your great articles
and insight. We sure will miss you!
We have a 38-foot Carver on the
Tennessee River (Watts Bar Lake),
and it is not a trawler but suits us fine.
