Poly vee belt expiry?

[nicknorman]

Our Beta 43 has a TravelPower alternator run from a polyvee belt (6pk). The engine and hence the belt have done 1600hrs / 3 1/2 years from new. Tonight I had a quick check round the engine and noticed a lot of black dust on the swims at the side of the engine that wasn't there a few weeks ago, roughly aligned with the TravelPower belt. Although overall it looks fine and doesn't leave much black mark on my fingers, I did find one short length maybe 3 inches where one of the ribs has disappeared. I haven't had to tension it for over a year, tension is still fine so it hasn't stretched.

 

I do have a spare, but my question, for anyone more familiar with these things than me, is - is the belt going to expire shortly, in which case it would be sensible to replace it now, or will it carry on for a good while yet? With the belt in general looking fine, I am slightly reluctant to replace it but on the other hand, would rather do so before it fails.

 

Bearing in mind that most of the time the engine is running it isn't doing anything except whirling round (although of course when it is working hard it is transferring 2 - 3 kw of power - kettle or tumble drier on) is 1600hrs a fair life or an unreasonably short one? The belt (same width) for the 175A alternator looks fine despite having worked harder I would have thought.

[Paul C]

Replace belts on condition, not age/mileage. Always carry a spare, they don't really "go off" or have a shelf life.

[bigste]

Dust under the belt is a sign of slipping but most belts will slip at some time. As been said, it's not the age it's the condition. Vee belts drive on the sides of the belt not the bottom of the belt. A new belt will sit proud of the pulley. If the belt is well down inside the pulley and there is lots of black dust then maybe a change is due. A well adjusted belt will go on for many years. Tell tale of a worn out belt is when it screams on acceleration even though it's adjusted correctly. The screaming is the slipping and as it's adjusted correctly it has probably lost too much off it's sides.

[Arthur Brown]

Cost of replacement vs. cost of a day with no mains and maybe flat batteries, you make the decision. I'd be tempted to replace the belt.

[Timleech]

How are you checking the tension? It can be more critical with a polyvee belt than with a plain vee or wedge belt.

 

Tim

[bargemast]

It's your boat Nick, if she would have been mine, I would change the belt before it breaks at an unforseen moment.

 

But now that you're aware of it's condition you'll keep an even closer eye on further wear, and may get a bit more service from your actual belt.

 

Peter.

[nicknorman]

Thanks guys. I think "close monitoring" is what I'll do for now, if only to learn how the belts degenerate. If it does break I don't lose any critical services, but I suppose there is a chance that the flying belt might damage something.

[nicknorman]

How are you checking the tension? It can be more critical with a polyvee belt than with a plain vee or wedge belt.

 

Tim

As per the instructions - 10mm deflection to a firm push centre span. But also, if it is just a little slack it tend to make complaining noises under load at low rpm (max belt load) and the correct tension seems to be just enough to prevent this. Both the TravelPower and the domestic alternators have overrun clutches that are supposed to prolong belt life. Hmmmm...

[RLWP]

Getting wrapped up in the other belt would be the issue if it came off. I can imagine a glorious mess if it got caught up and wrapped between the pulley and the timing cover

 

Is this 'not replacing the worn belt' thing something to do with living in Scotland?

 

Richard

[nicknorman]

Getting wrapped up in the other belt would be the issue if it came off. I can imagine a glorious mess if it got caught up and wrapped between the pulley and the timing cover

Is this 'not replacing the worn belt' thing something to do with living in Scotland?

Richard

Yes that's my worry. And belts -there are 3!. Yes, definitely something to do with living in Scotland.

 

Anyway, I don't mind replacing it if it is worn, it is just that, apart from the dust and the small section of missing rib, the belt looks as new, no fraying or cracking and no recent loss of (adjustment-critical) tension. Hence the thread to try to determine if it actually is worn.

 

If I hadn't noticed the short section of missing rib (engine at a lucky point of rotation)I wouldn't have known (or guessed) which of the 3 belts it was coming from.

Edited September 1, 2014 by nicknorman

[frangar]

I would much rather be changing a belt on a cold engine tucked up somewhere safe than removing bits of belt where it has taken the water pump belt off on a fast flowing river.....I personally change stuff like belts and pump impellers at least every couple of years even if no signs of wear....peace of mind is worth a lot.

 

Cheers

 

Gareth

 

Edited to add.....

 

Why don't you consider a piece of missing rib wear??....I'm glad I don't fly in your aircraft!

Edited September 1, 2014 by frangar

[RLWP]

Do you do the same with tyres?

 

It's worn out - replace it

 

And at the same time, see if it has somehow been slipping on the drive pulley. If the engine runs and the belt is stationary that would cause a localised worn patch

 

Richard

I would much rather be changing a belt on a cold engine tucked up somewhere safe than removing bits of belt where it has taken the water pump belt off on a fast flowing river

 

Even more fun trying to call out a mechanic to take the drive pulley off to get the wrapped up belt out whilst approaching a weir

 

Richard

[nicknorman]

I would much rather be changing a belt on a cold engine tucked up somewhere safe than removing bits of belt where it has taken the water pump belt off on a fast flowing river.....I personally change stuff like belts and pump impellers at least every couple of years even if no signs of wear....peace of mind is worth a lot.

Cheers

Gareth

Yes I think this is a good thought. I was not sure of the real-world consequences of a shed belt for a non-critical service, but I guess we can't preclude taking out other belts which are critical.

Do you do the same with tyres?

 

 

Most definitely. But then both my subaru and my Hayabusa eat tyres so one needs to extract the maximum they have to offer!

It's worn out - replace it

 

OK Dad.

[RLWP]

Being serious (for a moment), your most likely scenario is that it is going to slip. I'm wondering if it is already slipping momentarily, then taking up. If you did continue your belt wear experiment, I wonder if the bald patch gets longer.

 

Richard

[Timleech]

Info on setting belt tension here, pages 5 & 6.

As an aside - a few weeks ago, my wife went below to make some tea, using the electric kettle.

Shortly after switching it on, there was a seriously worrying rattling coming from the engine room, reducing the revs stopped it but it came back with increased revs.

When it was safe to do so, I stopped the engine expecting to find the pulley on crankshaft or alternator hanging loose. Everything was fine in that department, just the belt tension was a bit low. The belt must have been 'slipping and grabbing' and somehow creating the mechanical sound from the alternator.

 

Tim

[Flyboy]

If you have some of the ribs missing it's going to fail pretty soon. The ribs usually crack if the belt goes around an idler which bends the belt back on itself, a common problem on cars. Obviously any belt should be changed on condition. My advice is to change it now.

[nicknorman]

Being serious (for a moment), your most likely scenario is that it is going to slip. I'm wondering if it is already slipping momentarily, then taking up. If you did continue your belt wear experiment, I wonder if the bald patch gets longer.

 

Richard

I don't think it's slipping. It has 6 ribs, only one of which has a short section missing. The ribs adjacent (parallel) don't look distressed at all. And as I said, its life mostly consists of passing no load. We have the TravelPower on for less than 10% of the time, and when we do the load is often very low, and virtually never above 2kw (rated load 3.5 kw) so relatively speaking it has an easy life. On no load the TP alternator has very little drag and you can hear it overrunning on its clutch when you go into neutral from cruise, or when you stop the engine.

[andyb116]

If you take the belt off and turn it inside out you'll probably find it's badly cracked, this is normally due to age and heat where the rubber on the ribs has gone hard and brittle. This is a common problem on French diesel automotive engines, the vibration caused by the missing bits quite often damages the damper, tensioner brgs and power steering pump brgs. I'm sure a new 6pk belt and a bit of labout would be considerably cheaper than having to have the travel power alternator brgs replaced. Hope this helps.

Edited September 1, 2014 by andyb116

[nicknorman]

If you have some of the ribs missing it's going to fail pretty soon. The ribs usually crack if the belt goes around an idler which bends the belt back on itself, a common problem on cars. Obviously any belt should be changed on condition. My advice is to change it now.

No idler on this engine, just the two pulleys. But I guess if rib bits are missing that is telling me something! I'll at least take it off for a close inspection even if my acquired Aberdonianism makes me put it back on again!

 

What is the failure mode anyway? Presumably failure of the structural strands of whatevertheyare inside, rather than rubber failing?

If you take the belt off and turn it inside out you'll probably find it's badly cracked, this is normally due to age and heat where the rubber on the ribs has gone hard and brittle. This is a common problem on French diesel automotive engines, the vibration caused by the missing bits quite often damages the damper, tensioner brgs and power steering pump brgs. I'm sure a new 6pk belt and a bit of labout would be considerably cheaper than having to have the travel power alternator brgs replaced. Hope this helps.

It does, thanks.

[andyb116]

Also a common cause of freewheel clutch pulley failure (read expensive) :-((

[nicknorman]

Also a common cause of freewheel clutch pulley failure (read expensive) :-((

Ok you've got me scared now. 30 mins left to get back to the marina, then I'll replace it.

 

Edit: replace THEM ie the other polyvee for the 175A alternator as well, since I am not totally confident I have correctly identified the source of the new profusion of black dust.

Edited September 1, 2014 by nicknorman

[RLWP]

I don't think it's slipping. It has 6 ribs, only one of which has a short section missing. The ribs adjacent (parallel) don't look distressed at all.

 

That's a much less serious case than I was envisioning. I would be parsimonious and keep an eye on it. If it starts to shed more bits of rib, change it

 

I'm no one to advise on belts though. Recently I checked the oil on Tawny and spotted a black, knotty thing on top of the alternator. It was the entire outside band of the vee belt . The rest was still there and working (sort of) like a small section vee belt. I have replaced it

 

Richard

[nb Innisfree]

Our poly vee on the 70amp engine alt has always been a bit borderline and needed changing fairly regularly whereas the twin 13mm vee belts on the large 100 amp 24v alt are virtually maintenance free.

 

I think it's down to the fact that most alternators need to be spun fast so require small pulleys which can't be handled very well by normal v belts. Our large alt is a slow revving one so a 2:1 pulley ratio is ok allowing a largish 3" pulley which suits the simpler and more trouble free standard v belts.

 

Given more time and facilities I would consider a setup using toothed timing belts and sprockets from a car engine.To get the required speed two belts and four sprockets could be used giving a 4:1 ratio via an idler sprocket. No slip and very few boat engines exceed 4k rpm so max alt speed would be 12k.

 

ETA: Or maybe twin poly vee via same idler pulley setup.

Edited September 1, 2014 by nb Innisfree

[Timleech]

 

I'm no one to advise on belts though. Recently I checked the oil on Tawny and spotted a black, knotty thing on top of the alternator. It was the entire outside band of the vee belt . The rest was still there and working (sort of) like a small section vee belt. I have replaced it

 

Richard

 

Are you sure you weren't being over cautious, and not getting your money's worth?

 

 

Tim

[RLWP]

 

Are you sure you weren't being over cautious, and not getting your money's worth?

 

 

Tim

 

I've been very kind so far and not picked up on your use of an ELECTRIC KETTLE!

 

Richard