constantly shredding belts

We have an older Grand Banks 42 with Ford Lehman 120s. Ever since we purchased her four years ago we've had an ongoing issue with very short lived belts on the port engine. I've looked as closely as I can at pulley alignment and all seems well, I recently installed a new alternator and the problem persists. The water pump pulley turns freely...I even just installed those new universal belt tensioners from Balmar and the problem hasn't gone away. Typically were getting 15 to 20 hours out of a belt on the port engine and an entire season from the belt on the starboard engine...completely stumped

What are the sizes of each alternator?

What does the belt look like when the engine is running?

Possible issues:

cheap belts
high loads (e.g., alternator, pumps)
defective pulley (burr, alignment)
Pulley resistance?
improper tension or alignment adjustment

Any corrosion on pulley vee faces? Rough surface will wear belts fast.

What Bill said. Watch the belt at cruise rpms. If there is something missing on the mount it may be moving around.

The starboard unit it a 55 watt Leece Nevilke the port is an Ample Power 100 amp. The 100 amp alt is a recent addition. Nothing seems whacky while under way as far as I can see and these have all been Gates belts on both engines. I think I've looked at all the obvious problems and none seem to be at play here.

OK to be clear, the belt shredding was going on before you installed the new alternator? If so, are you 100% sure there is nothing wrong with the crank pulley?

Send a picture from the front and the side. Do you have ribbed belts?

Yes, the problem was there before we switched alts, and no we don't run ribbed belts. Capt Bill I've done a visual inspection and I can't see any obvious problems which is why this is such a mystery

You say you change belts each season? What say other Lehman owners? My belts look like new as do the pulleys, after 11 years on the PS 225 TIs.

Have you tried taking the temperatures of the various pulleys after shutting down the engines? This may give you a clue to the culprit.

Boydster said:

Yes, the problem was there before we switched alts, and no we don't run ribbed belts. Capt Bill I've done a visual inspection and I can't see any obvious problems which is why this is such a mystery

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Is there a lot of belt dust on that engine before the belt gives out?

sunchaser said:

You say you change belts each season? What say other Lehman owners? My belts look like new as do the pulleys, after 11 years on the PS 225 TIs.

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A bit of drift... but yes I look for wear as an indicator....years matters less than hours probably..

But after 5 years, I would be changing them as they can deteriorate.

I put 2 belts on that the PO had left aboard before last years trip to Fla. The first lasted nearly the whole trip, the second didn't make it across the Chesapeake from St Michaels to Baltimore. Both separated between layers...only the first actually broke, the second just sepataed and I caught it that night checking on it for tension.

I think he used to run an Ozone Generator in the bilge...maybe I should check my hoses as well.........

psneeld said:

A bit of drift... but yes I look for wear as an indicator....years matters less than hours probably..

But after 5 years, I would be changing them:

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But after one year or fifty hours is pretty extreme. As mentioned by others, several things to consider, especially small pulleys which can create too tight a turn radius.

Maybe these marinized Fls are not always the overall reliable engines they are made out to be.

sunchaser said:

But after one year or fifty hours is pretty extreme. As mentioned by others, several things to consider, especially small pulleys which can create too tight a turn radius.

Maybe these marinized Fls are not always the overall reliable engines they are made out to be.

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absolutely...I would expect them to wear out or get suspect from age....not just "fail".

I may be reaching for 3 years but as it may have lived in the bilge/engine room waiting it's turn...that's probably my PM schedule for belts unless they wear sooner than that...but I'm expecting about 1500 hrs at that rate. That's with the OEM, low output alternator.

Bomac (the parts and engine distributer) has yearly on their maintenance schedule. I find that excessive for quality belts. Who ever did that on older cars?.... or even the family riding mower that gets about the same number of hours a year as many boaters and those belt lead a really rough life...

bligh said:

Have you tried taking the temperatures of the various pulleys after shutting down the engines? This may give you a clue to the culprit.

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I haven't tried that, great suggestion. I'll pull out the IR thermometer my kids got me at Xmas.
Re. Belt dust, there is evidence of dust in the area around the front of the engine. I've also had to dig a couple of balls of melted belt goo from the V of the crank pulley.
There was a previous reply questioning if I used ribbed belts which I do not, would those be a superior choice?

Boydster

Have you checked all the pulleys and sheaves to insure identical groove profiles? There is special "tool" for this. And the matched the belt profile accordingly? Again, have you checked sheave diameters to be sure you're not pulling too tight a radius?

Some additional detective work on your part is required with many good suggestions tossed out. The differences between grooved vs straight belts will not provide you the many years and hours your vessel belts should last, several basic things are at play here and not right.

Pulleys rusted???

Pulleys could have excessive wear, does the belt stand proud in the vee? If a pulley is worn the belt will ride in the bottom of the groove and slip because of a lack of contact area. Also are all the pulleys matched, meaning identical grooves? Good luck on your fix

Have you checked pulley run out?

Thanks for the feedback all; looks like I'll be back in the basement doing some more investigation!