Alternator Drive Belt Help Please

[dehlerdave]

I have a 1989 Yanmar YGM20 with a 35 amp alternator ( with ADVERC) charging 220a house batteries and 75a engine start. Recently after being out sailing with the battery voltage down to 12 - 12.4 ish when I start the engine, the alternator belt slips causing a squeal. This has been bad enough to break the belt on a couple of occasions. On the other hand, if the batteries are fully charged or nearly, everything is fine. The belt is always properly tensioned. Clearly something is amiss.

Is it likely to be the alternator (the output is fine and will quickly lift the battery voltage over 14.5v?
Is it a characteristic of the ADVERC or is this defective?
Should I be looking at some other cause?

Grateful for any guidance as Ive just shredded my second belt today.

Thanks

Dave

 

[wotayottie]

In all probability you are using car spares shop belts. They are a different crosss section profile - I think from memory the Yanmar ones are 13mm and the car spares 12.7. Result is that the belt bottoms out in the pulley rather than be gripped by the sides and rapidly starts to slip.

I also had a pulley failure on a 2GM so check that the two sides are still tightly together.

You can get the correct size belt from Fenner power transmissions.

 

[earlybird]

The 2GM20 I had chewed belts until I found that the crankshaft pulley was rusty. A session with a fine file and emery cloth transformed belt life. I used ordinary "A" section, 13mm belts from a local engineers merchant. There is a different, deeper 13mm standard called SPA wedge, which perhaps might not fit.
I would have thought that a belt in good condition would handle a boosted 35 amp alternator OK. The Yanmar raw water cooled engine drive belt has good wrap around the pulleys. My only other suggestion is the bearings of the alternator might be failing.

 

[oldsaltoz]

Quote:
I have a 1989 Yanmar YGM20 with a 35 amp alternator ( with ADVERC) charging 220a house batteries and 75a engine start.

Can you try running without the Adverc for a few starts, it could be that the extra charge load is causing the slippage. Not sure if this is adjustable or has somehow upped the demand on your alternator.

Might be easier and cheaper than removing the alternator for a bearing check.

FWIW I use Gates green stripe or green line belts on every engine I own, boat, cars and truck. no connection and no problems.

 

[PetiteFleur]

Another alternative vee belt is called a 'Cogged Raw Edge' belt, which transmit more Horsepower than regular or SPA belts. Try a Transmission suppler from yellow pages, like Fenner oe Bearing Services. Gates is a good brand.

 

[charles_reed]

You'll have to change the belt from the Yanmar type to one with "teeth" on the inside, a proper heavy duty belt.

I had exactly the same problem - take the old one along to any motor factors for the size.

Also check that the belts aren't bottoming in the pulleys - those need replacement occasionally.

I ran a 90-amp alternator on a 2GM - so it's quite simple.

 

[tri39]

Asa Charles says, you need a toothed belt, and make sure it's wide enough. It's not due to the 35AH alternator or the Adverc, the correct belt will easily do what's needed. There's a very good selection in Halfords if you take the existing one along for comparison.