Belt Tension

[Bostwick]

I have a 100 amp. Balmar alternator, new this year. It is driven by a 3/8 inch Gates belt, top quality. The belt is undersized (should have been 1/2 inch) and belt tension is critical if I'm to avoid squealing and wear. I bought a belt tension gauge and consulted Balmar, and the recommended tension is 140 pounds at install, 110 pounds after run in, and 60 pounds measured cold after run in. I made a jack out of a turnbuckle and can tension the belt to 60 lbs cold. It actually doesn't seem too twanging tight, but I'm mindful of not wrecking bearings. Any advice?

Do other folks measure V-belt tension? I read an article that said 9 of 10 seasoned mechanics, when tested, could not measure belt tension accurately by deflecting the belt with a finger.

[Training Wheels]

Do what I did and do the serpentine conversion. Much better!

[sailorboy1]

If you look at a Balmar regulator instructions for the belt loading I bet your 3/8" would be suggested to derate to maybe 80%. I have a 1/2" belt and my 100-amp alternator is derated 10%

I bet nothing is going to keep that belt tight for long if it is asked to do 100-amps (or 70) for long.

I just deflect mine by hand and as long as it's tight enough to not slip I figure it is OK

a serpentine kit would be nice, but not $500-1200 nice

PS- have a spare belt on board!

[leftbrainstuff]

I don't measure belt tension after having tensioned thousands of belts over the years. (former mechanic)

However undersized belt(s) or oversized belt load will really highlight low belt tension and pulley misaligment.

Overtensioning and overloading crank end and flimsy alternator mounts is also an issue.

More critical than measured belt tension is loss of tension. If you keep suffering this issue then you'll need to add another belt or a serpentine belt. Serpentine is preferred as keeping two belts evenly tensioned can be a challenge.

[Frankly]

Depending on how long you expect to be producing anything near 100 amps that 3/8 belt will be short lived and produce a lot of dust. Because I have a large 600 AH bank, I work on 1/2" belts pretty severely (I have tried them all) and my alignment is near perfect. I would first revisit the belt size and then looking at derating your alternator. Depending on the model of the alternator and the engine compartment temperature you are also likely to find that even solving the belt problem just reveals the next week link in the chain. 100 amp Balmar will not produce 90/100 amps for a couple of hours feeding into a deeply discharged battery bank without overheating. Small engine mode has been my go to operation and everybody (alternator, engine, belt) are all happy.

Frankly

[Bostwick]

I should have said that one of the first things I did was de-rate to 60 amps. That helps. I guess I just need to ensure really correct alternator installation, top quality belts, good pulley alignment and correct tension - all the things I'm doing now, and the situation is much improved.

[Cheechako]

I had trouble with an 100 amp alternator and 3/8 belt also. Weird thing was it didn't slip/squel with the Balmar regulator but did with the Ample power regulator. The Ample asked the alternator to put out more amps! (was an older Balmar series lll regulator though)
Have you tried a 1/2" belt on your sheaves? It may give more contact area even if it sticks out the top a little...
Strangely, my Cat had two 100 amp alternators , one on each engine. Neither would squeal with a 3/8 Greenstripe belt and AP regulators. Go figure. I tried and tried to realign the single engine I mentioned above but couldn't eliminate the squeal.

[Seymore]

Originally Posted by Bostwick

I have a 100 amp. Balmar alternator, new this year. It is driven by a 3/8 inch Gates belt, top quality....

On what engine? For example, if it's an Yanmar 3GM30, the contact angle on the alternator is small, so pretty well any belt slips, even if it's tightened to specs.

[Cheechako]

Originally Posted by Seymore

On what engine? For example, if it's an Yanmar 3GM30, the contact angle on the alternator is small, so pretty well any belt slips, even if it's tightened to specs.

My cat mentioned above had 3GM30's . No squeal. Go figure!

[Training Wheels]

Originally Posted by Seymore

On what engine? For example, if it's an Yanmar 3GM30, the contact angle on the alternator is small, so pretty well any belt slips, even if it's tightened to specs.

My serpentine doesn’t slip!