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Alternator belt slipping/screeching


pig

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Good morning

Since I upgraded the leisure battery bank to 4x 135Ah batteries, I've found that on starting up, the belt slips and screeches. If I keep the revs low it eventually stops and its fine.

I am getting through fan belts at an alarming rate (every 50 engine hours) probably due to me overtightening the belt to counteract it slipping.

If the boat has been sitting unused, the solar (2x 250w panels) charges the batteries, and the fan belt doesn't slip on starting the engine.

I presume the higher load on the alternator when initially charging a bank of partially discharged batteries is what causes the slipping?

For information the engine is a 3 cylinder 1litre Sole 26, and I changed the weedy original alternator for a Lucas A127 70 Amp jobby.

I am thinking that if the alternator had a larger pulley, the load would be less, and the squealing/slipping would stop?

I appreciate that the output would be reduced, and the tachometer would not read correctly, but I'm prepared to put up with that.

So - is this a sensible and practical solution, and if so -how easy is it to source different size pulleys for the A127? 

Thanks for any thoughts

 

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41 minutes ago, pig said:

Good morning

Since I upgraded the leisure battery bank to 4x 135Ah batteries, I've found that on starting up, the belt slips and screeches. If I keep the revs low it eventually stops and its fine.

I am getting through fan belts at an alarming rate (every 50 engine hours) probably due to me overtightening the belt to counteract it slipping.

If the boat has been sitting unused, the solar (2x 250w panels) charges the batteries, and the fan belt doesn't slip on starting the engine.

I presume the higher load on the alternator when initially charging a bank of partially discharged batteries is what causes the slipping?

For information the engine is a 3 cylinder 1litre Sole 26, and I changed the weedy original alternator for a Lucas A127 70 Amp jobby.

I am thinking that if the alternator had a larger pulley, the load would be less, and the squealing/slipping would stop?

I appreciate that the output would be reduced, and the tachometer would not read correctly, but I'm prepared to put up with that.

So - is this a sensible and practical solution, and if so -how easy is it to source different size pulleys for the A127? 

Thanks for any thoughts

 

Perhaps rig up a bypass cable to bypass one or two of the batteries using an isolator switch until those batteries are charged and then switch in the other or others. A water pistol aimed at the belt squirting water on it will keep it quiet and cool and make it last longer, could be rigged up with string on the trigger to the control position. You do at least have a multi rib belt and not an ordinary V belt driving it?

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Even a thin V belt should drive a 70 amp alternator without slipping providing it has sufficient warp on the engine and alternator pulleys. I wonder if the alternator pulley slot profile matches the engine pulley and the water pump pulley.

 

Take a new belt and twist it inside out. Then offer it into the pulley. The belt and pulley sides should be parallel and the belt should sit clear of the bottom of the pulley. Check all the pulleys in case you have the wrong profile belt. There are a few similar looking but different belt cross-sections and you need to match them to the pulleys.

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50 minutes ago, pig said:

I presume the higher load on the alternator when initially charging a bank of partially discharged batteries is what causes the slipping?

You presume correctly.

 

50 minutes ago, pig said:

I am getting through fan belts at an alarming rate (every 50 engine hours) probably due to me overtightening the belt to counteract it slipping.

I assume this is a V belt. If so, are you sure you have the right width? Is the bottom of the groove in one, or more pulleys shiny? If it is, you may have too narrow a belt. V belts work by gripping the sloping sides of the pulley. Too narrow a belt and it runs on the bottom, where there is much less surface area to grip, hence they slip. V belts are available in several widths. If you try a wider one, then the length may need to be increased so it will fit. A friend had this problem with a raw water pump.

Jen

 

51 minutes ago, pig said:

I am thinking that if the alternator had a larger pulley, the load would be less, and the squealing/slipping would stop?

Unlikely to help. Below a certain speed, the alternator won't be able to start charging. Generally, people want to speed up boat alternators as they run slow compared with vehicle installations.

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Innisfree had twin v belts for its high output alternator but they used to wear rapidly, I upgraded to notched v belts and problem was cured. Also I had probs keeping both belts evenly tensioned so I dispensed with one belt but the one remaining began to wear rapidly again, I refitted 2nd belt and accepted different tensions, never had probs again, in fact adjustment was rarely needed and belts lasted ages. 

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I'm curious, did you source an A127 with the same single bolt (pivot) mounting; or is this an improvised mounting using the far more common two bolt mounting A127?

The question is of course to do with the belt and pulley alignment.

A second, less common issue can caused by running a very tight belt on the usual two piece pressed metal pulley. The pulley can flex and widen whilst running and cause accelerated wear. One piece machined pulleys are available.

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Just now, Eeyore said:

I'm curious, did you source an A127 with the same single bolt (pivot) mounting; or is this an improvised mounting using the far more common two bolt mounting A127?

The question is of course to do with the belt and pulley alignment.

A second, less common issue can caused by running a very tight belt on the usual two piece pressed metal pulley. The pulley can flex and widen whilst running and cause accelerated wear. One piece machined pulleys are available.

 

Yes I meant to but forgot to mention pulley alignment. Good point about the horrid tin pulleys.

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Many thanks for the replies:

Biz - it's a notched v-belt (Gates 6217MC)

TB - I will check the belt profile next time I'm on the boat and report back

JIW - ditto with the pulleys

Eeyore - the alternator is mounted on the two lugs provided for the original alternator - they are too close together for the Lucas, so I mounted it on a length of 8mm studding through the lugs, shimmed to give the proper pulley alignment. I can only check the alignment by eye - is there a more accurate simple check? I will also check the alternator pulley as you suggest -there is an alternator rebuild/service bloke near me so I'll see if he has a better, machined pulley to suit.

I'll report back with any progress.

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If you Google 'Anti slip belt dressing' there is all sorts of stuff. Never used it myself, could be snake oil or could be wonderful. Was going to try it on the belts of a pillar drill but found that the right sized belt helped considerably!

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15 minutes ago, pig said:

Many thanks for the replies:

Biz - it's a notched v-belt (Gates 6217MC)

TB - I will check the belt profile next time I'm on the boat and report back

JIW - ditto with the pulleys

Eeyore - the alternator is mounted on the two lugs provided for the original alternator - they are too close together for the Lucas, so I mounted it on a length of 8mm studding through the lugs, shimmed to give the proper pulley alignment. I can only check the alignment by eye - is there a more accurate simple check? I will also check the alternator pulley as you suggest -there is an alternator rebuild/service bloke near me so I'll see if he has a better, machined pulley to suit.

I'll report back with any progress.

 

Depends on what you mean by "by eye". If it's just squinting along the belt then yes, there is a more accurate way.

 

There should be sufficient parts on the engine pulley that gives a flat face at 90 degrees to the crank axis. If you lay the edge, not the face, of a steel rule (not a tape) across these parts and in line with the belt run there is normally just the thickness of the pulley flange between the rule and belt. It is then easy to see if the belt and rule are parallel within a couple of mm. If push comes to shove you can use a length of wood but lay it on a flat surface (table) first to make sure its not warped.

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3 hours ago, Bee said:

If you Google 'Anti slip belt dressing' there is all sorts of stuff. Never used it myself, could be snake oil or could be wonderful. Was going to try it on the belts of a pillar drill but found that the right sized belt helped considerably!

Does work but not a long term solution.

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Update:

should have gone to Specsavers?

I travelled to the boat clutching my shiny new steel rule, as recommended by Mr Tony B. The alignment was poor - I moved the alternator back (towards the gearbox) by about 6-7 mm to get it in-line. There was no screech when I started up, but the batteries had been charged by the solar, so not a real test.

I also noticed that it was slightly skewed - the mounting was indeed, as suggested by Mr Eeyore, a twin bolt alternator mounted on a single (wide) lug - allowing a little skew. So I will deal with this as well.

I have some anti-squeal spray coming too, but hopefully I won't need it.

Thanks for the advice, and I will report back when we go off in a few days time.

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42 minutes ago, pig said:

Update:

should have gone to Specsavers?

I travelled to the boat clutching my shiny new steel rule, as recommended by Mr Tony B. The alignment was poor - I moved the alternator back (towards the gearbox) by about 6-7 mm to get it in-line. There was no screech when I started up, but the batteries had been charged by the solar, so not a real test.

I also noticed that it was slightly skewed - the mounting was indeed, as suggested by Mr Eeyore, a twin bolt alternator mounted on a single (wide) lug - allowing a little skew. So I will deal with this as well.

I have some anti-squeal spray coming too, but hopefully I won't need it.

Thanks for the advice, and I will report back when we go off in a few days time.

the spray will / may stop the squeal but not the cause (which is mis-alingment or lck of tension.

Toothed belts can help

a better solution (though more expensive) is to fit a flat belt (I forget the correct term) and suitable pulleys. Tha cured my problem AND frequent changes of belts!

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11 minutes ago, OldGoat said:

the spray will / may stop the squeal but not the cause (which is mis-alingment or lck of tension.

Toothed belts can help

a better solution (though more expensive) is to fit a flat belt (I forget the correct term) and suitable pulleys. Tha cured my problem AND frequent changes of belts!

But alignment is pretty critical with poly vee/multi rib/flat belts.

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Have a look at this extract from the Vetus parts manual for their Mitsubishi engine range.

The front leg of the alternator is clamped directly to the front of the mounting lug on the engine by the action of the sliding bush in the rear leg acting on the spacer (3). The front leg is clamped to the engine, and the rear leg is supported by the sliding bush. The bush is roughly the shape and size of a cotton reel, and needs to be long enough to prevent the sliding bush from falling out of the rear mounting leg when the bolt is tightened.

The alignment must be adjusted after the alternator is in position, adding or removing washers from behind the pulley.

When tensioning the belt you need to leave the through (2) bolt just loose enough to move (with some effort) the alternator, minimising the chances of the alternator twisting on the mounting.

 

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Edited by Eeyore
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A thick steel washer under the head of the through bolt will also help stabilise things. The legs on the alternator are thick enough in their normal use, but a bit on the thin size for this type of arrangement, hence the note on leaving the through bolt fairly tight during belt adjustment. You don't want to be trying to pull the alternator back into line using the through bolt after tensioning the belt.

Edited by Eeyore
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Brilliant. Thankyou so much. I had come up with the idea of a large flat washer at the front of the mounting bolt (now threaded rod), and the idea of tightening everything up just shy of locked, before tensioning the belt is a good 'un.

Cheers.

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The one big foot on the alternator is a poor engineering idea. I have had these break the bolt on several Vetus  alternators.

One particular boat has a big 24v twin belt alternator and it broke 14mm High Tensile bolts and shredded belts until I welded a proper rear mounting point onto the bracket and fitted a longer bolt.

 

I would be concerned about using threaded rod to secure this alternator, it is not high tensile and could easily snap.

Edited by Tracy D'arth
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I have retained the original 50amp ND alternator on my Mitsubishi, very difficult to keep in line when adjusting the belt. Often see other engines where the front face of the boss on the engine worn to a taper; no hope of alignment once that happens. Thorneycroft and Barrus had the right idea and bolted a fabricated mount to the pto flanges.

Edited by Eeyore
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Be careful with belt dressing spray. Yes it will solve the problem, but the downside is being sticky it amalgamates with the dust from the belts. That then gets sucked through the cooling ducts into the alternator and hurled all round the engine by the belt. Result mess and overheating alternator.

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Or..... ask yourself why there is a squeal? I'm sure the solutions proposed are valid but I'd suggest that a nice smooth surface on the belt (which you will get fairly soon after the squealing starts) and a nice smooth surface on the pulley = limited grip / slipping / squealing.

So, whip the belt off and take one of those nice cheap sanding blocks to the V surfaces of the pulley - you just want to 'bust' the glaze all the way round. If the belt is over shiney as well, rough that up a wee bit - don't take too much material off.

You are just trying to promote grip and eradicate slip (ie squeal) so gently does it.

A crude solution but it usually works for me.

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If you've got a squeal, I'd suggest you've got a shiny pulley. Once you've got a shiny pulley you're always going to have a shiny pulley, unless you do something about it. A shiny pulley will have less grip = belt less likely to grip = shiny belt = squeal. Vicious circle. A new belt will be quickly converted.

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20 minutes ago, Opener said:

If you've got a squeal, I'd suggest you've got a shiny pulley. Once you've got a shiny pulley you're always going to have a shiny pulley, unless you do something about it. A shiny pulley will have less grip = belt less likely to grip = shiny belt = squeal. Vicious circle. A new belt will be quickly converted.

Are you a belt retailer looking to improve his sales figures? 

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Engineering officer: How long will it take?

Tiffy: About 2 hours.

Engineering officer: You've got 10 minutes before we sink.

Tiffy: Ok, I know a bodge that'll work, if I can get hold of a sanding block in the next 10 minutes.

 

Beyond that I'll be sticking to established engineering methods; "v" belt drives have been around for about 100 years, so we must have been doing something right all this time.

 

 

Edited by Eeyore
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