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A loose belt/dodgy alternator..... or something worse?


Froggy

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We've only had our boat a few weeks, as per other threads i've posted. The surveyor pointed out some engine squeal and we had a basic engine service done before taking possession, including a new alternator belt, In two days of sailing there was occasional squeal, mainly when the engine started from cold, but now it's got worse.

 

I had a try at tightening the alternator yesterday, but in the cramped space i think it's a two person job, unless there's some tool to lever the alternator with one hand whilst tightening the belt. To any extent i managed to tighten it, it hasn't resolved the issue. I noticed that if the noise settles down you can then rev the engine up without a problem, but if you bring the revs down and then rev up again the noise returns. Also, when the noise disappears at a low idle the rev counter climbs up a little, even though to me there was no discernible increase in revs. We know we have dodgy leisure batteries and someone on another thread suggested this might be part of the issue. Any thoughts?

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How tight is the alternator belt?

 

One good test is that you should - just - be able to twist it through 90 degrees at the mid point between main pulley and the water pump. You don't want to over-tighten it.

 

Or alternatively, if you pick the mid-point on the longest side, can you deflect it by more than a centimetre (say) to either side.

 

(Obviously both these tests are carried out when the engine isn't running! :lol:).

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Could be a heave current going into knackered batteries. Do you have a ammeter installed

No ammeter unfortunately, but the batteries are pretty knackered. If the consensus is that this is the problem we'll change them. We were hoping to delay this expense until the spring since we're moored up with a shoreline until the end of February. Will this issue risk damage to the engine? We will need to run it regardless of the shoreline since the Eberspacher isn't wired up to that circuit and only charges off the alternator.

 

EDIT: I have a hand held unit with two probes that I think incorporates current readout. At what points on the four-battery bank (6V batteries) should i connect these, presumably at the main positive out and earth leads? From memory I think the main positive out is connected to one of the centre batteries but might be mistaken.

 

 

How tight is the alternator belt?

 

One good test is that you should - just - be able to twist it through 90 degrees at the mid point between main pulley and the water pump. You don't want to over-tighten it.

 

Thanks for this. The belt isn't too tight though, it's possibly a little loose if anything. However, whilst the bottom alternator looks decent (Barrus Shire), the top one looks pretty ropy, a fair bit of rust, and is made by some obscure Korean company.

Edited by Froggy
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No guarantees offered but I used to find with car engines in the dim and distant past that squealing had a lot to do with load on the alternator but also the state of the pulleys. A heavier load AND a nice shiney pulley permitted more squealing. So grab some glass/emery paper or something similar and bust the glaze on the pulleys. Nothing too radical, just spoil the shine. When the belt is gripping rather than slipping you should lose the squeal.

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All the symptoms of belt slip.

 

The mid point deflection is the test for a standard V belt, the 90 degree twist is for a PolyV.

 

What size (amps) is the alternator? What type of belt? and if its a standard V how wide is it?

Some installations have less in reserve than others. What size are the pulleys? Using a good quality notched belt can sometimes help on a marginal installation. Also not all belts have the same depth, it is just possible that the new belt is wrong and too deep for the pulley groove.

Is everything clean and dry?

A suitable length of timber can often be used (with common sense and care) to hold the alternator to tension the belt whist tightening the alternator bolts. Three hands helps but it can usually be done with just the two.

 

................Dave

 

edited to change timer to timber

Edited by dmr
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No guarantees offered but I used to find with car engines in the dim and distant past that squealing had a lot to do with load on the alternator but also the state of the pulleys. A heavier load AND a nice shiney pulley permitted more squealing. So grab some glass/emery paper or something similar and bust the glaze on the pulleys. Nothing too radical, just spoil the shine. When the belt is gripping rather than slipping you should lose the squeal.

 

 

All the symptoms of belt slip.

 

The mid point deflection is the test for a standard V belt, the 90 degree twist is for a PolyV.

 

What size (amps) is the alternator? What type of belt? and if its a standard V how wide is it?

Some installations have less in reserve than others. What size are the pulleys? Using a good quality notched belt can sometimes help on a marginal installation. Also not all belts have the same depth, it is just possible that the new belt is wrong and too deep for the pulley groove.

Is everything clean and dry?

A suitable length of timer can often be used (with common sense and care) to hold the alternator to tension the belt whist tightening the alternator bolts. Three hands helps but it can usually be done with just the two.

 

................Dave

 

Many thanks for all this useful information. I'll have a good look when i'm back at the boat later in the weekend and will report back. If it's only a loose belt I'll be pleasantly relieved. :)

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Take note of what Brian says. On the basis of what you have told us only I too suspect faulty batteries although that does not mean the belt is not a bit loose as well but we have no way of knowing on-line.

 

 

If it turns out to be the batteries (and they are definitely pretty knackered, the boat was standing at a brokerage for a few months and, additionally, as I've looked more closely around the boat I'm not convinced the last owner was too hot on any maintenance that involved expenditure in latter years) can we get away with this for a few months without risking damaging the engine? I don't suppose it would do the alternator any good, but assuming it's the top one that is charging the leisure batteries (I need to check when I return to the boat) it looks as if it will need replacing shortly anyway.

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If any pulleys are rusty in the V through a long period of no usage the rust will wear the belt walls rapidly and it will keep slackening off the belt.

 

Thanks. I'll have a closer look over the next few days, maybe tomorrow if we can fit it in with people coming to visit and other stuff.

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Two alternators on one belt? that's quite a load on one belt. Maybe there isn't a very good 'wrap' around one of them and it needs to be really tight to work. If one of the alternators is very close to the block then the belt might just be skimming a small section of the circumference of the pulley. Its all guesswork though, might be worth swinging the alternators out on their adjustment and getting a longer belt? Any bearing and power transmission supplier could probably supply a belt a few mm longer. Only a thought.

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'

Why dont you charge all batteries from your shore supply?

 

We are, but the Eberspacher battery isn't linked into the circuit. I think the four 6v leisure batteries are in such a poor shape that the Victron isn't putting much charge into them.


Two alternators on one belt? that's quite a load on one belt. Maybe there isn't a very good 'wrap' around one of them and it needs to be really tight to work. If one of the alternators is very close to the block then the belt might just be skimming a small section of the circumference of the pulley. Its all guesswork though, might be worth swinging the alternators out on their adjustment and getting a longer belt? Any bearing and power transmission supplier could probably supply a belt a few mm longer. Only a thought.

 

 

Try a belt dressing. Available from all good belt stockists in an aerosol. It makes the belt very sticky which in turn gives more grip to the pulley.

 

Again, very useful advice, much appreciated.

 

Am heading off back to the boat soon and will only have internet access on my phone for a day or two, so apologies for any delay in further responses.

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An alternator should be designed so it can not deliver more than its design load so you should not be able to burn the alternator out by trying to charge batteries with shorts in them but they will (eventually) stink, gas and may explode if you carry on for long periods. If the problem is lack of capacity then it should not cause a significant problem for the alternator.

 

If you carry on with the squealing then you may ruin the belt.

 

Personally I would just buy a pair of batteries for now to see if it stopped the squeal and add more as you can afford them. However there is no guarantee it is a battery problem, you may be over discharging them so they are way bely the "accepted" 50% of fully charged as maximum discharge.

 

On no account try to use an ordinary multimeter to measure alternator output. Typical non-clamp type multimeter can only read to 10 and in some cases 220 amps. After that the shunt inside burns out and if it does that when connected to a charging circuit it may well take the alternator with it.

 

 

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The possible poor state of the batteries is a bit of a red herring as far as belt squeal is concerned, though important for the safety reasons stated by Tony. Even with perfect batteries an alternator will frequently be required to deliver its full output so should be able to do so without belt squeal, but do note that some alternators may overheat if called upon to deliver full output for a long time.

Belt dressing is no substitute for finding out what is wrong and fixing it.

 

Some people would say that a brief squeal when you first start the engine with cold belts is acceptable, but its still far from ideal.

Check the pulleys, get a nice notched belt from Gates and tension it correctly. The notched belt really helps if you have a very small diameter pulley.

 

..............Dave

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Can someone explain why battery condition has any relation to belt squeal. I cannot see any relationship between the two.

 

Sure.

 

Discharged battery = will draw lots of current from alternator.

Alternator working hard = it becomes a heavy load to be driven by the engine.

Heavy load driven by a pulley = belt slips.

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Sure.

 

Discharged battery = will draw lots of current from alternator.

Alternator working hard = it becomes a heavy load to be driven by the engine.

Heavy load driven by a pulley = belt slips.

Which means in the OPs case that the belt has to transmit approx 3 hp to the domestic alternator pulley via a contact area of no more than 2 square inches. This assumes from earlier posts that its a Barrus Shire with one belt passing around four pulleys. Belt life on these engines varies considerably from annual, on a just in case basis; to almost as regular as oil changes. It seems likely that belt life on this particular installation is closely related to how deeply you allow the batteries to discharge between engine starts; and in this case dead batteries appear to the alternator as very discharged.

Edited by Eeyore
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The time has come really where, like most vehicles these days to use multi-V belts arranged in the serpentine method, involving many guide rollers and automatic tensioner, to give maximum belt wrap around pulleys. Probably beyond the skills of most engine marinisers though, or I think they would have already had a go at it.

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Still don't get it. Doesn't the alternator pulley rotate at the same speed regardless of battery draw. What I mean is; engine revs are 1000 rpm at tickover. Alternator pulley is rotating at 10,000 rpm. Why does a heavy battery draw make the alternator pulley harder to rotate?

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The time has come really where, like most vehicles these days to use multi-V belts arranged in the serpentine method, involving many guide rollers and automatic tensioner, to give maximum belt wrap around pulleys. Probably beyond the skills of most engine marinisers though, or I think they would have already had a go at it.

 

Yeah but don't we actually like our boat engines to be as low tech as we can get away with, no electronics, no fancy expensive things to go wrong etc.

 

We have a polyv belt on the travelpower, its not ideal with poor wrap, I have thought about fitting an idler to sort this out but its just not easy to find a suitable place with something to fix to. Also from my previous work stuff I know that an idler in the wrong place is not good at all.

I still reckon several separate belts driving separate alternators and things is the way to go, with an individual polyV for any really big alternators.

Sounds like the op has the worse of both worlds....a single belt driving lots of things....trying to do the job of a serpentine system.

 

...........Dave

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Still don't get it. Doesn't the alternator pulley rotate at the same speed regardless of battery draw. What I mean is; engine revs are 1000 rpm at tickover. Alternator pulley is rotating at 10,000 rpm. Why does a heavy battery draw make the alternator pulley harder to rotate?

You can't generate power for nothing on this planet, which what your saying. Solar power is the nearest to it, but even that is wearing out the sun faster than it would if left alone.

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