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Tensioning fan/drive belt


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#1 Horsehorn

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Posted 04 April 2012 - 12:57 PM

Hi,

I've got a squeel/screech and low charging batteries and am wanting to increase the tension of my two drive/fan belts to rectify this as they are a little loose. Can anyone explain how I can do this? The screech is only for a couple of seconds when turning the engine on and revving the engine.

With the alternator belt I think I have succeeded in tightening it by jamming a screwdriver into the altenator vents so that I can stop the belt turning around when I tighten the nut, but I can't do the same for the belt which is linked to the water pump. How can I stop the belt from moving, and which nuts should I be tightening? I've been told that if tensioned correctly the belts should 'ping' or I should be able to twist it 1/4" in the centre of the belt. I know that I should be able to tell if they are tight enough when the starter battery reads 14.4V+ (right?) and the leisure's are 12.3-12.7V.

A friend did tell me how but their explanation has evaporated into thin air inside my brain.

According to a succestion in another post I put a little washing up liquid on the belt but this didn't change anything, and I'm not sure if the belt should be moistened anyway.

The engine is a BMC 1.5, no pics to hand unfortunately.

Thanks everyone,

Lucy
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#2 David Schweizer

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Posted 04 April 2012 - 01:16 PM

Tensioning your alternator belt is unlikely to have any lasting effect. if it is too tight it will wear and the squealing will recurr. The problem you identify is quite common on the BMC 1.5 if a larger output alternator has been fitted without modifying the pulleys as well, but as it only happens for the first few seconds, I would try to learn to live with it. Alternatively, you could run the engine on fast tickover for a couple of minites until the belt has warmed up and then increase ther revs to achieve maximum charging.

The main problem is that the BMC 1.5 was designed to drive a 35 amp alternator, the 9.5mm wide belt is fine for that, but as soon as a larger alternator is introduced the belt needs to apply more purchase to drive it without slipping. The standard solution is to have the drive pulley machined out to 14mm amd fit a wider pulley onto the alternator, this is what I had to have done on our engine and the squealing dissapeared.

I do not know where you are located, but I could give you the contact details of someone in Braunston who would be able to do the job for you.

Edited by David Schweizer, 04 April 2012 - 01:55 PM.

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#3 nicknorman

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Posted 04 April 2012 - 01:39 PM

The main problem is that the BMC 1.5 was designed to drive a 350 amp alternator...

Wow, wish we had bought one of those instead of our Beta with a proxy 175 amp alternator! :lol:

But seriously, adjusting or at least checking the belt would probably still be a good idea since it may be too loose anyway.

You don't need to stop the alternator / belt from rotating, just need to move the whole thing further out. Typically there is a slotted rod, you loosen the bolt attacking that to the alternator, loosed the other alternator mounting bolt that acts as a pivot, then push the alternator out to the side (maybe with some extra leverage) so as to set the tension correctly, then retightn everything.
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#4 IDS

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Posted 04 April 2012 - 01:41 PM

Lots of examples on youtube show the general principles of checking and adjusting drive belts.
Easier to view than describe.

e.g. youtubeClip
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#5 David Schweizer

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Posted 04 April 2012 - 01:57 PM

Wow, wish we had bought one of those instead of our Beta with a proxy 175 amp alternator! :lol:

But seriously, adjusting or at least checking the belt would probably still be a good idea since it may be too loose anyway.

You don't need to stop the alternator / belt from rotating, just need to move the whole thing further out. Typically there is a slotted rod, you loosen the bolt attacking that to the alternator, loosed the other alternator mounting bolt that acts as a pivot, then push the alternator out to the side (maybe with some extra leverage) so as to set the tension correctly, then retightn everything.

Yes, a typo crept in. I meant 35 amp , but I suspect you already knew that! Earlier post modified.

Edited by David Schweizer, 04 April 2012 - 01:58 PM.

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#6 bizzard

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Posted 04 April 2012 - 02:07 PM

Yes, a typo crept in. I meant 35 amp , but I suspect you already knew that! Earlier post modified.

Those 1500 engines of course originally drove dynamos with the skinny v belts when in early vehicles and boats and were just about adequate for driving the later 35 amp alternator but as you say,asking for squeals trying to drive any higher output alternator.
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#7 Grace & Favour

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Posted 04 April 2012 - 02:16 PM

Wow, wish we had bought one of those instead of our Beta with a proxy 175 amp alternator! :lol:

But seriously, adjusting or at least checking the belt would probably still be a good idea since it may be too loose anyway.

You don't need to stop the alternator / belt from rotating, just need to move the whole thing further out. Typically there is a slotted rod, you loosen the bolt attacking that to the alternator, loosed the other alternator mounting bolt that acts as a pivot, then push the alternator out to the side (maybe with some extra leverage) so as to set the tension correctly, then retightn everything.


I'd suggest using more peace-oriented bolts as well....:lol:

Edited by Grace & Favour, 04 April 2012 - 02:16 PM.

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#8 by'eck

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Posted 04 April 2012 - 02:18 PM

Hi,

I've got a squeel/screech and low charging batteries and am wanting to increase the tension of my two drive/fan belts to rectify this as they are a little loose. Can anyone explain how I can do this? The screech is only for a couple of seconds when turning the engine on and revving the engine.

With the alternator belt I think I have succeeded in tightening it by jamming a screwdriver into the altenator vents so that I can stop the belt turning around when I tighten the nut, but I can't do the same for the belt which is linked to the water pump. How can I stop the belt from moving, and which nuts should I be tightening? I've been told that if tensioned correctly the belts should 'ping' or I should be able to twist it 1/4" in the centre of the belt. I know that I should be able to tell if they are tight enough when the starter battery reads 14.4V+ (right?) and the leisure's are 12.3-12.7V.

A friend did tell me how but their explanation has evaporated into thin air inside my brain.

According to a succestion in another post I put a little washing up liquid on the belt but this didn't change anything, and I'm not sure if the belt should be moistened anyway.

The engine is a BMC 1.5, no pics to hand unfortunately.

Thanks everyone,

Lucy


Not sure why you are attempting to jam screwdrivers into the alternator fan blades to stop it turning :o

To tension the belt(s) the alternator mounting bolts are loosened & the alternator as a whole is swung out on its pivots to increase belt tension.

This usually involves identifying the long pivot bolt and securing nut if it has one (purple arrow) and a second bolt at the front of the alternator which locks it in a particular position in the slot of a long bracket (green arrow). The alternator body can then be swung out increasing its distance from the crank drive pulley & therefore tensioning belt(s).

A lever can help maintain the tension whilst you first tighten the bolt in slotted bracket then the pivot bolt (green then purple).

When correctly tensioned there should be just a half inch of movement when the belt is tugged at the point of the thick black arrow. Excessive tension will reduce the life of the alternator rotor bearings.

Sometimes there is a third tensioning bolt (red arrow) which makes the whole process easier.

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Regards - Richard

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#9 Albion

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Posted 04 April 2012 - 02:33 PM

But whatever you do to lever the alternator outwards to tension the belt use the lever against a solid part of the casing. DO NOT stick levers into ventilation slots etc and use those to lever or you may well end up having to buy a new alternator which won't be service exchange because you've damaged the casing.
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#10 nicknorman

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Posted 04 April 2012 - 03:53 PM

I'd suggest using more peace-oriented bolts as well....:lol:

The curse of the iPad automatic "correct"-spelling-as-you-type strikes again!

Edited by nicknorman, 04 April 2012 - 03:53 PM.

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#11 Horsehorn

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Posted 04 April 2012 - 04:54 PM

[quote name='David Schweizer' timestamp='1333545390' post='849997']
Tensioning your alternator belt is unlikely to have any lasting effect. if it is too tight it will wear and the squealing will recurr. The problem you identify is quite common on the BMC 1.5 if a larger output alternator has been fitted without modifying the pulleys as well, but as it only happens for the first few seconds, I would try to learn to live with it. Alternatively, you could run the engine on fast tickover for a couple of minites until the belt has warmed up and then increase ther revs to achieve maximum charging.

Thanks all, that explains it I think, especially Richard Hula's diagram.

David - The noise isn't the problem really, it's that we have low charging batteries and it's been suggested that this might be why, so unfortunately I don't think I can leave it.

The alternator was changed to a 75amp from a 50amp when we bought the boat last year, but have not experienced any screeching until the last few weeks. Is there any specific reason why things will have changed?

Thanks all,

Lucy
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#12 Tony Brooks

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Posted 04 April 2012 - 05:25 PM

Thanks all, that explains it I think, especially Richard Hula's diagram.

David - The noise isn't the problem really, it's that we have low charging batteries and it's been suggested that this might be why, so unfortunately I don't think I can leave it.

The alternator was changed to a 75amp from a 50amp when we bought the boat last year, but have not experienced any screeching until the last few weeks. Is there any specific reason why things will have changed?

Thanks all,

Lucy



They probably fitted a new belt when they changed the alternator and new belts do tend to stretch a little so it is now a bit slack.
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#13 bizzard

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Posted 04 April 2012 - 05:28 PM

I'd say that since fitting the 75amp Alt the belt has been slipping a bit and so has prematurely worn the two gripping surfaces of the belt to become glazed and shiny,hence more slip and the squeal.

Edited by bizzard, 04 April 2012 - 05:29 PM.

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#14 David Schweizer

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Posted 04 April 2012 - 06:30 PM

Thanks all, that explains it I think, especially Richard Hula's diagram.

David - The noise isn't the problem really, it's that we have low charging batteries and it's been suggested that this might be why, so unfortunately I don't think I can leave it.

The alternator was changed to a 75amp from a 50amp when we bought the boat last year, but have not experienced any screeching until the last few weeks. Is there any specific reason why things will have changed?

Thanks all,

Lucy


The recent incidence of belt screeching could be a consequence of a loosening/stretching belt, in which case tightening should help. Or it could be the consequence of trying to replenish increasingly flat batteries, in which case you need to increase the alternator output.

Fitting a higher output alternator will not automaticly improve charging, especially if it is one of the older type Lucas A127 models which are machine sensed. What you need is a either a Battery sensed alternator, or an external regulator designed to convert the Alternator to Battery sensed, which will assess how much charge your batteries need and deliver the appropriate amount, but first a couple of questions:-

Do you know what type of alternator you have fitted?

Do you have an ammeter fitted, and if so what charge rate is it recording?

Do you have an independant alternator regulator (Sterling, Adverc, Smart guage etc)? If not it may be worth considering having one installed. Before I fitted a Sterling Advanced Alternator Regulator on our boat the alternator output was around 15 amps, after fitting it has increased to an initial 55 amps, and floating at about 35 amps, which usually re-charges the batteries within a couple of hours after overnight usage.

I am sure that Snibble (our resident alternator expert) will be along shortly to correct all my technical mistakes.

Edted to add:-
if you are still using a 9.5mm belt on a 75 amp alternator, you definitely need to modify your pulleys to take a 14mm belt.

Edited by David Schweizer, 05 April 2012 - 09:48 AM.

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#15 nicknorman

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Posted 04 April 2012 - 09:06 PM

Fitting a higher output alternator will not automaticly improve charging, especially if it is one of the older type Lucas ACR models which are machine sensed. What you need is a either a Battery sensed alternator, or an external regulator designed to convert the Alternator to Battery sensed, which will assess how much charge your batteries need and deliver the appropriate amount, but first a couple of questions:-
...
Do you have an independant alternator regulator (Sterling, Adverc, Smart guage etc)? If not it may be worth considering having one installed. Before I fitted a Sterling Advanced Alternator Regulator on our boat the alternator output was around 15 amps, after fitting it has increased to an initial 55 amps, and floating at about 35 amps, which usually re-charges the batteries within a couple of hours after overnight usage.


Sorry David but I really don't subscribe to the need for battery sensed alternators nor fancy independant regulators. These are both substitutes for adequate wiring between alternator and batteries, and the cheapest and most reliable and most elegant solution is to install adequate wiring (if not already so installed).

Once the OP has fixed the belt-slipping issue it might be a good time to check volt drop between alternator and batteries (both +ve and -ve lines) during initial charge, and only if those amount to more than say 0.5 volt at max charge current is it worth doing anything about it.

FYI on our Beta 43 with Iskra 175 amp machine sensed alternator and no charge regulator gadgets, initial charge current is 175amp (with the engine at idle, since pulley ratios are well designed) with a total voltage drop around 0.5 volts because the cabling is all 70sqmm. Of course the volt drop falls to near zero once the current drops during the last 25% or so of charge
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#16 David Schweizer

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Posted 05 April 2012 - 06:19 AM

Sorry David but I really don't subscribe to the need for battery sensed alternators nor fancy independant regulators. These are both substitutes for adequate wiring between alternator and batteries, and the cheapest and most reliable and most elegant solution is to install adequate wiring (if not already so installed).

Once the OP has fixed the belt-slipping issue it might be a good time to check volt drop between alternator and batteries (both +ve and -ve lines) during initial charge, and only if those amount to more than say 0.5 volt at max charge current is it worth doing anything about it.

FYI on our Beta 43 with Iskra 175 amp machine sensed alternator and no charge regulator gadgets, initial charge current is 175amp (with the engine at idle, since pulley ratios are well designed) with a total voltage drop around 0.5 volts because the cabling is all 70sqmm. Of course the volt drop falls to near zero once the current drops during the last 25% or so of charge

I agree that if I had a Beta 43 engine with an Iskra 175 amp alternator in our boat, I probably would not find the need for an externat regulator either, but we are taliking about someting quite different, although until the OP comes back with more information, it is difficult to identify where the problem may lay.

I do understand that expensive modern alternators do not require external regulators, but older designed machines, such as the ubiquitous Lucas A127(and it's imitations) do benefit from them being fitted. This whole area was the subject of much debate between ChrisW and Gibbo some years ago, and whilst there was never a consensus of opinion, I seem to remember that the final reluctant outcome was that it depends on the particular machine.

At the moment we do not know what machine Lucy has in her boat, nor do we know how she can tell that there is not much charge, and until those questions are answered, there is little advice that can be given, other than trying to re-tension the belt. However, I have my doubts about this as a solution, as the squealing is not continuous but only when she initially revs the engine on starting. My experience of a loose belt is that the squealing is fairly continuous.

One thing we have not asked Lucy is whether there is evidence of a lot of black dust around the alternator pulley, that would indicate a seriously slipping belt.

Edited by David Schweizer, 05 April 2012 - 09:47 AM.

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#17 by'eck

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Posted 05 April 2012 - 08:23 AM

Sorry David but I really don't subscribe to the need for battery sensed alternators nor fancy independant regulators. These are both substitutes for adequate wiring between alternator and batteries, and the cheapest and most reliable and most elegant solution is to install adequate wiring (if not already so installed).

Once the OP has fixed the belt-slipping issue it might be a good time to check volt drop between alternator and batteries (both +ve and -ve lines) during initial charge, and only if those amount to more than say 0.5 volt at max charge current is it worth doing anything about it.

FYI on our Beta 43 with Iskra 175 amp machine sensed alternator and no charge regulator gadgets, initial charge current is 175amp (with the engine at idle, since pulley ratios are well designed) with a total voltage drop around 0.5 volts because the cabling is all 70sqmm. Of course the volt drop falls to near zero once the current drops during the last 25% or so of charge


:smiley_offtopic: Interesting view point Nick. Clearly they are of use with older alternators putting out less than say 14.5 volts.

Even when used with a modern alternator though I still subscribe to the use of external DAR's for several reasons:

1) It gives you greater control of the alternator output with regard to battery type, absorb & float voltages etc. with true multi-stage charging.

2) LED or even digital readout info is available with most of them so you know not just that its working but at what charge phase its in.

3) Following on from 1) less gassing is likely once batteries are fully charged. Not an issue with most boaters but I like you plan on doing extensive cruising with long days of engine running.

4) Battery sensing is available with most of them (temperature & voltage). I know you raised the issue of inadequate cable size between battery & alternator but even when cabled properly it gives you an edge over machine sensing. It also allows the voltage drop of a conventional diode splitter to be negated.

5) If it fails you can still fall back to the alternators internal regulator by unplugging it or maybe breaking just one wire.

I agree that most of these points would be redundant if alternators existed that effectively had an onboard DAR, but do such animals exist with external sensing?

I would also be interested to know if your alternator puts out 14.5 volts or thereabouts indefinitely.

Edited by richardhula, 05 April 2012 - 08:51 AM.

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#18 Nickhlx

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Posted 05 April 2012 - 09:02 AM

I'd say that since fitting the 75amp Alt the belt has been slipping a bit and so has prematurely worn the two gripping surfaces of the belt to become glazed and shiny,hence more slip and the squeal.


I would agree with that, even possibly the side surfaces are doing little gripping now and it is relying on the bottom of the belt to try to transmit the power - this will wear quickly if it is, needing more frequent
adjustment ....

Only answer really is to up the belt size, fit a dual pulley system or a toothed belt system if you need the bigger alternator output...

Nick
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#19 bizzard

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Posted 05 April 2012 - 10:35 AM

I would agree with that, even possibly the side surfaces are doing little gripping now and it is relying on the bottom of the belt to try to transmit the power - this will wear quickly if it is, needing more frequent
adjustment ....

Only answer really is to up the belt size, fit a dual pulley system or a toothed belt system if you need the bigger alternator output...

Nick

Too much belt slip over a long period will also wear the pulley V-groove to the point where even a new belt will sink into it and probably touch bottom,it also polishes up the pulley V-walls which makes the slippage progressively worse.
If Lucy's belt encompasses three pulleys,perhaps its original water pump as well this would reduce the belt to pulley contact even more.If this is the case,by fitting a double pulley to the crankshaft so that the inner pulley groove drove the water pump and the outer groove drove the alternator only, a much larger grip area ''wrap around'' on both crankshaft and alternator pulley's would be obtained and so probably stop the slipping. The alternator would have to be moved forward a pulley grooves width though
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#20 Nickhlx

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Posted 05 April 2012 - 10:55 AM

Too much belt slip over a long period will also wear the pulley V-groove to the point where even a new belt will sink into it and probably touch bottom,it also polishes up the pulley V-walls which makes the slippage progressively worse.
If Lucy's belt encompasses three pulleys,perhaps its original water pump as well this would reduce the belt to pulley contact even more.If this is the case,by fitting a double pulley to the crankshaft so that the inner pulley groove drove the water pump and the outer groove drove the alternator only, a much larger grip area ''wrap around'' on both crankshaft and alternator pulley's would be obtained and so probably stop the slipping. The alternator would have to be moved forward a pulley grooves width though


I am sure, years ago, I remember some compound being available to improve grip on belts, making the surfaces more sticky - sounded like a bit of a temporary fix, but can't recall the details...

Belt to pulley grip is a combination of area and force between the surfaces, so more wrap around, bigger belts or tighter tension will all help, but with the caveat of too much tension will wear bearings in mind...

When I fitted the over-run pulley to the Beta 43's Iskra 175, the alternator had to be moved forward a touch to keep the pulleys in line - fortunately is was only a few millimetres and washers were all that were needed as the bolts were long enough

Nick
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