Mys­tery of the miss­ing ‘teeth’

Canal Boat - - Back Cabin: Experts -

QWhen check­ing the al­ter­na­tor belt on our boat I no­ticed many of the ‘teeth’ were miss­ing. The belt had been on for 12 months and is a good make. I ad­just it each time be­fore we set off (10mm free play). The belt is 1025x10: do I need a thicker one? Is it nor­mal to have to ad­just the belt ev­ery four to five hours? MAG­GIE ALLEN, via email

ATONY REPLIES… You should not have to ad­just the belt ev­ery four or five hours once it has bed­ded in. The ‘10’ fig­ure is the width of the belt. On a 10mm belt I would not want to try driv­ing any­thing much over 70 amps (with 90 amps as an ab­so­lute max­i­mum).

Have a look here: scribd.com/doc/52177682/V-belt-se­lec­tion. You will see they list two dif­fer­ent belts with a 10mm top width, Z and SPZ, but they have dif­fer­ent bot­tom widths which means the belt face an­gles are dif­fer­ent. This must be matched to the pul­leys in use, oth­er­wise you will get slip­ping and ex­cess wear. Take an un­worn belt, twist it inside out and push it into each pul­ley in turn. There must be an air gap be­tween the belt (oth­er­wise the belt is too thin) and the bot­tom of the pul­ley and the pul­ley sides and belts faces must be ex­actly par­al­lel (oth­er­wise the an­gle is wrong).

Use a straight edge on the front of the crankshaft pul­ley to en­sure that the belt runs from that pul­ley are par­al­lel with it. If not, use wash­ers to pack the al­ter­na­tor front bracket un­til they are. ( The back bracket of­ten has a slid­ing bush that will ad­just it­self for the new length).

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