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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 08-28-2008
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alternator

Hello all,
>>
My alternator making a screeching sound when revving up form 1000 and 1500 rpm at the initial starting of the engine and then it goes away after 3 to 5 minutes of engine running. Is the alternator going bad?
Nelson
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Old 08-28-2008
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Most likely belt tension..shouldn't be able to depress it but maybe 1/2" with moderate pressure from a couple fingers mid way between pulleys..Id start there.
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Old 08-28-2008
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Sounds like a worn or loose belt. Check tension and treat belt with conditioner or replace belt.
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Old 08-28-2008
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Yes, tighten the belt a bit and I am pretty sure it will go away.
At low revs, for a given power output, the tension has to be higher than at high revs.
It tends to slip at lower revs.
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Old 08-28-2008
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Or put some soapy water on it (revitalizes the rubber in the belt or some such thing).
Temporary fix tho, if tightening it up doesn't do it and the soapy water does you need a new belt.
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Old 08-28-2008
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Yeah, I agree with all of the above. In addition, I'd check the belt for any glazing or cracking. If noted, replace. I'd also check for correct fit. I was told years ago by a Gates rep., IIRC, that a 'v' belt should fit into the pulleys no more than 1/16th of an inch above the groove and no more than
1/8th of an inch below to insure a proper fit.

Another source of slippage is misalignment from pulley to pulley. You can check this with a straigt edge or by eyball if you have access to align the pulleys up by line of sight.

The 1/2 inch deflection of the belt is a good test, but another way of checking if you have enough tension on the belt is to get a rag and with a good grip on the cooling fins of the alternator pulley, try to make the pulley slip in either direction. If it does, adjustment is in order. Good luck.

Bob
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Old 08-28-2008
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thank you so much for information and I try all over this weekend.
many thanks to all.
nelson
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Old 08-29-2008
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"Or put some soapy water on it " Ouch! Never! Never put soap on rubber, it rots the rubber and gives it a better grip for a while--but then the rotten rubber fails. Drag racers used to soap their tires to get better traction at starts.

There's never been a belt maker that recommeneded any "belt dressing" or other magic in a can, it can't solve anything that proper pulley alignment, belt tension, and a good belt can't solve without the goo.

Too much belt tension can also ruin the alternator and engine bearings, and squeaing *could* mean an alternator bearing is failing--not just the belt. Better to check the belt condition, check for correct tension, and then check pulley alignment. If it still squeals, and the squeal is coming from the alternator, pull it and check for bearing problems. If the bearings freeze you've got a bigger problem.
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