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ASK THE EXPERTS
SOLUTIONS FROM THE BoatU.S. TECH TEAM
WE HAVE A 1993 CHRIS-CRAFT THAT EATS ALTERNATOR BELTS. Late last
summer, the alternator belt broke. We replaced it and that one broke also. Since
then, we have had a new alternator and several belts replaced only to have the
belt break once again. The alignment has been checked by two marine mechanics both times. They have tried without success to find out why the alternator
belt keeps breaking. This latest one lasted a week before breaking. What else
should we look for that would cause the belts to break? Rick Carson
DON CASEY: There are several possibilities. The most common cause of premature belt
failure on a boat is rust. All of your pulleys need to be rust-free and as smooth as silk inside
the V. Just one little lump of rust will tear at the belt several thousand times a minute. Remove
the belt and inspect every pulley it runs over, using the tips of your fingers to feel for roughness. If you find any, remove it by wet-sanding. It is a good idea to protect a rehabilitated
pulley with paint. While you have the belt off, check the bearings of all the components this
belt drives. It might be that you have a failing bearing in your water pump. Turn all pulleys by
hand, feeling for any roughness or drag. Replace anything suspect. Your new alternator does
not get a pass here, particularly if it is a rebuilt unit.
heat up and wear. A length of arrow-straight
dowel dropped into the empty pulley slots
is good for revealing alignment problems.
You will need to recheck alignment after you
install and tension the belt. Here a straight
edge on the face of the pulleys should expose
Finally, suspect the belt. The proper belt
sits slightly above the pulley sides on all of
the pulleys. If the new belt sits lower, it is
too small. Not all belts are created equal. I
have personally experienced belts purchased
from national auto supply chains that died
in hours just from poor construction. Gates
Green Stripe belts enjoy a sound reputation.
The right belt won’t need to be over-tightened,
another common cause of failure. Tighten only
enough so that turning the alternator pulley by
hand rotates the crankshaft pulley.
HOW BIG IS BIG ENOUGH?
I have a Shannon 37 ketch, and my goal
is to go cruising. The boat has a 45-pound