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Drive belt - toothed or smooth


Mike at Mayroyd

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You have a 'cogged' belt which is fine. This type of belt is more flexible & better suited to the smaller pulleys fitted on alternators. If I were you I would fit another cogged belt as it will probably last a lot longer than a solid one.

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I have a BMC 1500 Tempest. I have replaced the original 35 amp alternator with a 55 amp one and have run out of adjustment for the drive belt and will buy a shorter one. The one that is fitted has teeth, is this usual? The pulleys are a smooth V profile

 

Yes this is quite normal where the belt has to go round and grip a small pulley. A solid belt would not form into the small pulley and grip it and thus turn the alternator.

 

Have you put the pulley from the old alternator onto the new one or is the pulley on the new alternator the same size as the old one?

 

Did you fit a new belt with the new alternator? Could be the old belt is stretched and needs a simple replacement.

 

ETA Just a suggestion, take a piece of rope roughly the same thickness as the belt is wide, or thicker, loosen the alternator adjustment, put the rope around the pulleys as tight as possible, mark both bits of the rope with a marker and then measure to get a good idea of the size need.

Edited by Geo
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Thank you. Pulley on new alternator is smaller

 

 

In that case suggest, loosening the alternator adjustment right off, measure and get a new belt slightly smaller than the measurement. BTW just thought, when you measure make sure the alternator does not move from its maximum adjustment point. That is the sort of silly I do. smile.png or should that be minimum

 

ETA just read this not sure it make sense. Adjust the alternator to the position that would take the smallest belt then measure

Edited by Geo
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Gates belts are probably the best these days. Cogged, raw edge is the kiddie. You will probably need a belt only slightly smaller. I take it that the old alternator was an Lucas ACR and the new one is an A127 in which case the old pulley won't fit the new alternator.

 

Edt. The new alternator could be an ACR, but would normally be 45amp. The ACR type has a big black plastic case on the back with only Lucar push on terminals, the A127 have Lucar type push on and stud terminals and no black plastic case on the back. You may need to upgrade the main thick wire from the alternator to a thicker one to take the extra current. Those old ACR 34amp alts often had quite a skinny wire there.

Edited by bizzard
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