Rats! The belt’s so squeaky

Canal Boat - - Engine & Gearbox Directory - AN­DREW MALKIN, via email TONY REPLIES…

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.

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