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Old 08-10-2018, 06:11 AM   #1
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Alternator belt

Ok...1984 270 with a now new alternator, new pulley 2.5in, new belt, and cleaned drive pulleys. The belt has broken 2x after non-stop squeaking and significant heat. Silent belt when alternator harness is unplugged (no load). Checked pulley alignment and looks perfect. Regularly checking belt tension and is tight but not too tight...I am using NAPA belts. What am I missing here?
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Old 08-10-2018, 07:51 AM   #2
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Hi

Do you have an electrical short on the output of the alternator? One way that could happen is you have one or more dead batteries .....

Bob
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Old 08-10-2018, 08:49 AM   #3
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Does the belt youíre using fit the drive pulley? If the belt is too narrow it will drop onto the bottom of the pulley instead of riding on the shoulders of the ďVĒ. This will cause slippage = heat = damage = breakage.

Just throwing that out there.
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Old 08-10-2018, 09:32 AM   #4
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Using Napa part xl 7465. Top of belt is flush with edge of all pulleys. Part look up says this is right part number...
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Old 08-10-2018, 09:44 AM   #5
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Recheck your electrical connections, disconnect and then see if Alt spins smoothly, sounds like the Alt is "locked" when energized.
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Old 08-10-2018, 12:17 PM   #6
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When disconnected, it does spin smoothly with no belt squeak. Itís only squeaking when itís under a load trying to charge
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Old 08-10-2018, 12:36 PM   #7
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What mechanism regulates the Amps that the alternator produces? Maybe I should check that for proper function? I have a newish red top battery for chassis and checked out good
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Old 08-10-2018, 01:42 PM   #8
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What mechanism regulates the Amps that the alternator produces? Maybe I should check that for proper function? I have a newish red top battery for chassis and checked out good
Hi

An alternator has a voltage regulator on it that limits the voltage it puts out. The current is limited by the resistance of the windings. If you try to run one into a short ... it'll put out a lot of current .. A multimeter will tell you if the alternator is putting out the right voltage. It also will tell you if your batteries are at some crazy low voltage.

Bob
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Old 08-10-2018, 02:31 PM   #9
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Quote:
Originally Posted by J. Morgan View Post
Does the belt youíre using fit the drive pulley? If the belt is too narrow it will drop onto the bottom of the pulley instead of riding on the shoulders of the ďVĒ. This will cause slippage = heat = damage = breakage.

Just throwing that out there.


V belt pulleys CAN wear out, but it takes a LOT of use to do that, usually hundreds of thousands of miles.

You might try one size wider belt just for kicks. I have done that with worn pulleys with great success.

I just donít believe that a typical alternator can be loaded up enough to snap belts.... something else is up in my opinion..... maybe your Napa got hold of a bad batch?
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Old 08-10-2018, 02:32 PM   #10
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Hi

An alternator has a voltage regulator on it that limits the voltage it puts out. The current is limited by the resistance of the windings. If you try to run one into a short ... it'll put out a lot of current .. A multimeter will tell you if the alternator is putting out the right voltage. It also will tell you if your batteries are at some crazy low voltage.

Bob
and when the alternator dies, it usually takes the VR with it. Listen to Bob!
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Old 08-10-2018, 02:41 PM   #11
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Thanks bob, the alternator that was replaced tested putting out almost 15v. I have not checked the new one but maybe there is some electrical gremlins outside of my alternator hardware and there is nothing wrong with the belt...
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Old 08-10-2018, 04:08 PM   #12
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Iím going to try a larger belt and battery check. This week the belt broke with a new Napa belt on a new pulley mounted to a new alternator. It squeaked non stop for about 20 miles then failed with the heat build up. The rubber on sides of the belt was slick and partially melted
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Old 08-10-2018, 04:10 PM   #13
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Did you ever think that it maybe the water pump ???
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Old 08-11-2018, 09:11 AM   #14
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Iím going to try a larger belt and battery check. This week the belt broke with a new Napa belt on a new pulley mounted to a new alternator. It squeaked non stop for about 20 miles then failed with the heat build up. The rubber on sides of the belt was slick and partially melted
Hi

Continuing to run into what likely is a fault in the electrical system is a very good way to do a *lot* of damage to the electrical system. The cheapest part of it would be burning out the new alternator. Frying this and that downstream in the system simply adds to the bill. Worst case is probably a fire. Having a fire in an RV is no fun at all. Having that when moving 60+ mph down the road .... yikes !!!

Bob
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