Rats! The belt’s so squeaky
QI have had an irritating intermittent high-pitched squeak from the alternator/water pump on my three-cylinder Beta engine for virtually the whole of the six years I have owned my boat, despite fitting a new water pump and belt.
It is worst when I switch the inverter on, but sometimes it squeaks when we are just cruising while charging the starter battery plus two 110Ah batteries. Sometimes it doesn’t squeak at all, other time it starts then fades and disappears and on other occasions it squeals like a demented rat. I have noticed sticky, almost powdery fragments of rubbery residue near the belt. My engine runs quite cool and my batteries charge. Any ideas?
AThe rubber granules, plus symptoms indicating it is worse with a large electrical load, point to a slipping belt. A single ‘V’ type belt should not be relied upon to drive an alternator over 70-90 amps maximum (although some people seem to get away with driving larger alternators). If your alternator output is higher, investigate fitting a wide flat poly-V belt or twin V belts. Boats usually use the smallest alternator pulley diameter possible and that requires a notched or cogged belt.
The rubber powder could be a symptom of the alternator pulley being out of alignment with the crankshaft and water pump pulleys. That would quickly wear the belt so it would tend to slip. Use a straight edge on the engine pulley to ensure the belt run to the alternator is parallel to the straight edge.
There are two belt profiles that most people call ‘V belts’ (the ‘V’ profile and the ‘wedge’ profile) and different dimensions in each group. In the past, someone might have fitted a pulley that does not match the other two, or the wrong belt may have been fitted: to check, take the belt off, twist it inside out and push it into each pulley in turn. The belt profile should exactly match the pulley profile, with a clear air gap between belt and pulley bottom.
Finally, try a quality belt like Fenner or Brammer rather than whatever the local source has in stock. Tension to just 10mm deflection in the middle of the longest run under moderate finger pressure.