Belts on marine engines

[peter bush]

Given that most marine engines are idle for most of their life,especially on sailing boats,and given that most seem to demolish drive belts with disappointing regularity,is there not a case for rethinking the method of operation? For example I can ,with a bit of a struggle,undo the relevant nuts,lever the alternator away from the engine,set the correct tension , do up the nuts,rebuild the cockpit,replace the cabin furniture,start the engine and in 5 minuits see pieces of rubber flying around the engine space and the belt is as slack as it was before. I know all about making sure that the pulleys are in line,and nicely polished, and decent belts,etc etc but ,and here my thought process gets a bit scrambled, if that belt has been tight for some time,surely any elasticity.....and I recognize that it will be very small.. .will have gone. So are there any compelling reasons for not having a spring loaded tensioning device that could be slacked off during periods of inactivity .I am aware that it would be one more thing to do before getting underway,seacocks battery sailcover et al,but that's sailing. I think that I have read that vee belts don't really like being bent the "other" way, but it would'nt be much and not,in terms of overall engine life,for very long. Iam thinking of some sort of over centre lever arrangement that puts sufficient tension on the belt and ,in the right place,would provide more wrap round on the alternator pulley. Or has this been done already? Or am I reinventing the wheel?

 

[BabaYaga]

Or am I reinventing the wheel?

I think the wheel might be invented already, in form of the poly vee/multi rib/serpentine belt.
After 10 yrs/500 hrs I´m still using the original belt on my Beta Marine 20 hp.

 

[NormanS]

Given that most marine engines are idle for most of their life,especially on sailing boats,and given that most seem to demolish drive belts with disappointing regularity,is there not a case for rethinking the method of operation? For example I can ,with a bit of a struggle,undo the relevant nuts,lever the alternator away from the engine,set the correct tension , do up the nuts,rebuild the cockpit,replace the cabin furniture,start the engine and in 5 minuits see pieces of rubber flying around the engine space and the belt is as slack as it was before. I know all about making sure that the pulleys are in line,and nicely polished, and decent belts,etc etc but ,and here my thought process gets a bit scrambled, if that belt has been tight for some time,surely any elasticity.....and I recognize that it will be very small.. .will have gone. So are there any compelling reasons for not having a spring loaded tensioning device that could be slacked off during periods of inactivity .I am aware that it would be one more thing to do before getting underway,seacocks battery sailcover et al,but that's sailing. I think that I have read that vee belts don't really like being bent the "other" way, but it would'nt be much and not,in terms of overall engine life,for very long. Iam thinking of some sort of over centre lever arrangement that puts sufficient tension on the belt and ,in the right place,would provide more wrap round on the alternator pulley. Or has this been done already? Or am I reinventing the wheel?

There is something wrong with your installation if you have " bits of rubber flying around the engine space......) after five minutes running.

 

[macd]

I think the wheel might be invented already, in form of the poly vee/multi rib/serpentine belt.
After 10 yrs/500 hrs I´m still using the original belt on my Beta Marine 20 hp.

+1.
On my first Beta the polyvee lasted 2000 hours and was only changed because I thought it was about time. It needed no adjustment whatever after initial bedding-in. (If I may clarify the 'rib' bit: lateral ribs (as opposed to the longitudinal ribs on polyvees) are simply a means of reducing destructive heat build-up in the fabric of the belt. They do little or nothing for grip on the pulleys.)

Fitting V-belts on marine diesels is taking the p**s.

 

[Hydrozoan]

… lateral ribs (as opposed to the longitudinal ribs on polyvees) are simply a means of reducing destructive heat build-up in the fabric of the belt. They do little or nothing for grip on the pulleys. …

On an older V-belt Beta I have found that a cogged belt eliminated the light shedding which had not been dealt with even by careful cleaning of pulley surfaces.

I attribute part of the benefit of a cogged belt as reduced distortion in the side walls of the belt as it bends round a pulley wheel of very small radius, compared with the greater side wall distortion which I think (considering the geometry of the belt cross-section) must happen to some extent with a solid belt.

You may be right about heat build-up being the main issue, but I think the above may be an alternative, or at least additional, factor – though I haven’t done any searching on the subject, and so may be completely wrong.

 

[macd]

I attribute part of the benefit of a cogged belt as reduced distortion in the side walls of the belt as it bends round a pulley wheel of very small radius, compared with the greater side wall distortion which I think (considering the geometry of the belt cross-section) must happen to some extent with a solid belt.

You may be right about heat build-up being the main issue, but I think the above may be an alternative, or at least additional, factor – though I haven’t done any searching on the subject, and so may be completely wrong.

I believe both are just different ways of describing the same thing, Hydrozoan: the reduced section at the 'cogs' reduces internal friction, which is a major cause of heating. (I know rather more about this in respect of tyres, but the principle is essentially the same.)

 

[PlankWalker]

Must be something wrong with your installation.
My Perkins has had the same toothed Vee belt for 17 years

Plank

 

[vyv_cox]

My Yanmar 3GM30F has had one belt replacement in 2300 hours, about 16 years since original installation. The original belt looked OK and still had the silver paint on it but I noticed that the flanks were worn a bit so I replaced it, about 1800 hours I think but not certain. There is no reason why any installation should last as well as that unless an over-large alternator is being used to charge heavy battery banks but even then I would expect life in four figures.

 

[bikedaft]

Must be something wrong with your installation.


Plank

+1

when i got the boat the V section of (yanmar 3gm30f) alternator pulley wheel was clearly the wrong section for the belt (which was right for the crank pulley) so i changed the alternator pulley wheel.

 

[Sailorsam101]

Why have a belt at all? On motorbikes the alternator is gear driven from the engine.

A simple change to engine design would see this happen and then no more loose drive belts ever. The raw water pump on marine engines are not belt driven so why an alternator?

 

[RichardS]

Given that most marine engines are idle for most of their life,especially on sailing boats,and given that most seem to demolish drive belts with disappointing regularity,is there not a case for rethinking the method of operation? For example I can ,with a bit of a struggle,undo the relevant nuts,lever the alternator away from the engine,set the correct tension , do up the nuts,rebuild the cockpit,replace the cabin furniture,start the engine and in 5 minuits see pieces of rubber flying around the engine space and the belt is as slack as it was before. I know all about making sure that the pulleys are in line,and nicely polished, and decent belts,etc etc but ,and here my thought process gets a bit scrambled, if that belt has been tight for some time,surely any elasticity.....and I recognize that it will be very small.. .will have gone. So are there any compelling reasons for not having a spring loaded tensioning device that could be slacked off during periods of inactivity .I am aware that it would be one more thing to do before getting underway,seacocks battery sailcover et al,but that's sailing. I think that I have read that vee belts don't really like being bent the "other" way, but it would'nt be much and not,in terms of overall engine life,for very long. Iam thinking of some sort of over centre lever arrangement that puts sufficient tension on the belt and ,in the right place,would provide more wrap round on the alternator pulley. Or has this been done already? Or am I reinventing the wheel?

As others have suggested, the cheapest solution to stopping belt wear, assuming that your pulleys are correctly in line, is to fit an equivalent cogged belt ..... and make sure that the flat top of the belt is level with the outside edge of the pulleys. If your belt is "sunken down" at all into the pulleys you have the wrong section belt and it will wear very rapidly.

Richard

 

[RichardS]

Why have a belt at all? On motorbikes the alternator is gear driven from the engine.

A simple change to engine design would see this happen and then no more loose drive belts ever. The raw water pump on marine engines are not belt driven so why an alternator?

The coolant pump on marine engines is driven by the belt though!

Richard

 

[savageseadog]

The timing is gear driven rather than belt driven on proper marine engines. It would help if Yanmar fitted proper tensioners for the two remaining belts or were gear driven.

 

[Hydrozoan]

I believe both are just different ways of describing the same thing, Hydrozoan: the reduced section at the 'cogs' reduces internal friction, which is a major cause of heating. …

Perhaps they are – I was thinking about the belt walls bulging on a small pulley and the forces being borne disproportionately by the small area of the bulge on the belt wall surface, so producing dust - but it will of course heat the belt internally too.

(And writing that has made me think of Richard Feynman’s criticism of the school text book answer ‘Friction’ to the question why shoe leather rubs away – he said the child learned much more from the idea that ‘the sidewalk grabbed bits of the leather and tore them off’! )

I once had a bad problem with belt dust and eventually found that it came from the belt’s just rubbing on a nearby but apparently well clear Jubilee clip bolt – but only at a certain narrow band of engine speed and belt vibration which is why I didn’t spot it for some time! Something unexpected to look out for.

Even after dealing with that (and despite all the checking of alignment, temperature measurements and cleaning of wheels etc. that I performed) I still got some light dust which I found was eliminated with a cogged belt - so whatever the mechanism, I’m sticking with them (I was seriously thinking of buying the Beta polyvee retrofit kit until I switched).

 

[charles_reed]

I'd agree with general consensus that there is something wrong with your installation. A polyvee or serpentine belt is an expensive method of reducing wear, but a heavy-duty (cogged) belt on even a high output alternator (with a smart external controller) does about 600-800 hours.
Having solid, machined pulleys with no rust on bearing faces helps a lot.

 

[prv]

The raw water pump on marine engines are not belt driven

Some are

Anyway, there are no longer any engines being designed for yacht use (Bukh are the only dedicated small marine diesels I can think of, but the intended application is ships' lifeboats). My Volvo was designed for generators and refrigeration plant, I believe, neither of which need an alternator hung off the side.

They are all adaptations, even when brand new out of the factory, and a belt is a much easier adaptation than some kind of gear-train to the crankshaft.

Pete

 

[rogerthebodger]

They are all adaptations, even when brand new out of the factory, and a belt is a much easier adaptation than some kind of gear-train to the crankshaft.

Pete

Which would need lubrication and thus covers and seals on the shafts and seals in the alternator, etc so would be much more costly.

As others have said corrected sized, aligned and fitted with correct tension should last for even.

The main advantage of the poly vee belts is that they do not need tensioning adjustment as they have a very small stretch factor.

 

[Quandary]

Anyone got a tip for alternator belt tensioning?
my engine is below the floor, the alternator is secreted near the bottom of the pit hidden by a big green tube ( intercooler/heatexchanger?) the usual trick of using a wooden lever to push the alternator away from the block is not an option because the space available is insufficient and you can only get one hand down there at a time. I thought of trying to force a wooden wedge between the alternator and the block tapping it up from below but there must be a better way. The adjusting bolt goes through a U shaped spacer but I can not work out how to apply force there. Engine is VP TAMD 31.

 

[rogerthebodger]

Anyone got a tip for alternator belt tensioning?
my engine is below the floor, the alternator is secreted near the bottom of the pit hidden by a big green tube ( intercooler/heatexchanger?) the usual trick of using a wooden lever to push the alternator away from the block is not an option because the space available is insufficient and you can only get one hand down there at a time. I thought of trying to force a wooden wedge between the alternator and the block tapping it up from below but there must be a better way. The adjusting bolt goes through a U shaped spacer but I can not work out how to apply force there. Engine is VP TAMD 31.

I made up a special rigging screw to tension a jockey wheel tensioner on my engine. Considering doing the same on my 2 alternators.

Just left of the jockey pulley between the crankshaft and water pump pulley's

 

[Avocet]

I have a home-made alternator installation and for various reasons too tedious to explain, the belt gets a really hard time. 6" pulley on the engine, 1.25" pulley on the alternator. There was no way a V belt was going to work, so I tried a Poly V. That was better, but I still suffered high wear rates and loads of rubber dust. Now I have a timing belt doing the job and it has been fine ever since.