Why am I shredding belts on Yanmar?

tim3057 said:
I'm getting through alternator belts at an alarming rate - what's the principal cause? Too tight? Too loose?
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Too Tight..

Too Loose

Grooves too rough

Alternator set up overloading the drive

Wrong belts

Alternator axis out of line so pulleys not on the same axis


Could be one of many reasons or a combination.
 
On the alternator set up question - charging domestic battery (manual selection switch) makes a distinct drag on the engine note - almost as if the current drain makes alternator friction increase. Is this normal?
 
Yanmar belts are prone to this problem.

I have changed to using belts made by Gates, available from motor factors at far less than the cost of Yanmar branded belts. The belts are grooved rather than flat, last much longer and don't create dust. I'm about to start my fourth season on the same belt.

You don't mention which engine you have but for my 2GM20F (same belt on the 3GM30F), I use a Gates Extra Service No 6469 EXL AVX 13x975. The 13 refers to the width in mm & 975 the length. The belt for the freshwater cooled engine (2gm20/3GM30) is the same width but a different length.

It also helps if you use fine wt & dry sandpaper and rub any rust off the pulleys at the end of the season and put a layer of varnish on the surface. This soon wears off when you refit the belt the next season.

Hope this helps.
 
How are the belts deforming or breaking. If they are the type which has a vee'd shape to them, they wear at the sides, until the open end of the vee on the pulley allows them to touch the bottom of the vee of the pulley and then slips( and squeals too!)
There is a correct angle of vee'd belt for matching the pulleys.
If you still have the original belt the number/and circumference reference is on the outside of the belt. Halfords and other factors have several equivalents that will be cheaper than originals,like Fenners,Mintex .etc.
The fitters tension the belts by giving the belt a twist at the centre of the longest run and then try a 1/2" depression of the belt at the same point;it should not be able to twist fully if correct tension
The other possibility is that the pulley wheels are not in alignment with each other,with a sideways tension trying to strip an edge,and fails. If a toothed belt, and the correct type, then I suspect tension may be the culprit.

ianat182
 
Thanks Dave very helpful. Mine is a 2GM20 too, freshwater cooled which I guess is the 'F' suffix; seawater cooled = seawater circulating directly round the engine? If my engine's the same as yours (seawater passing through heat exchanger) then I'll order some Gates. Where do you get them from?
 
Thanks - I'll do the twist thing (I recall that trick from somewhere). Need to confirm belt length then I'll go to Halfords!
 
tim3057 said:
Thanks Dave very helpful. Mine is a 2GM20 too, freshwater cooled which I guess is the 'F' suffix; seawater cooled = seawater circulating directly round the engine? If my engine's the same as yours (seawater passing through heat exchanger) then I'll order some Gates. Where do you get them from?
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Yes - the F is indeed the suffix denoting a freshwater cooled engine. I contacted Gates and they said just go to my local motor factors with the reference numbers I have quoted and they should be able to order some. I bought two - one to fit and a spare - and they cost about £20 for the two.

The contact at Gates at the time was Iain Mitchell email IAINM@gates.com
 
tim3057 said:
On the alternator set up question - charging domestic battery (manual selection switch) makes a distinct drag on the engine note - almost as if the current drain makes alternator friction increase. Is this normal?
Click to expand...

Yes. A heavily loaded alt can take over a HP from the engine to drive it. The alternator is taking the engine power and converting it into electricity, so the heavier the load on the alternator the more power it takes to drive it.
 
I've had a Yanmar 2GM20 in my boat for the last 18 years. A very good reliable engine but for some reason it used to eat genuine Yanmar belts. Black dust everywhere and they had to be replaced every year or two once all the tensioning adjustment had been used up. Eventually tried a Halfords equivilant with "saw cuts" on the inside the problem disappeared. The current Halfords belt has been on for about 5 years and I can't remember the last time I had to re-tension it.
 
SteveIOW said:
I've had a Yanmar 2GM20 in my boat for the last 18 years. A very good reliable engine but for some reason it used to eat genuine Yanmar belts. Black dust everywhere and they had to be replaced every year or two once all the tensioning adjustment had been used up. Eventually tried a Halfords equivilant with "saw cuts" on the inside the problem disappeared. The current Halfords belt has been on for about 5 years and I can't remember the last time I had to re-tension it.
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Is it the raw water cooled version? Do you know what number or size it was?
 
Spyro said:
Is it the raw water cooled version? Do you know what number or size it was?
Click to expand...

Yes, the 2GM20 is the raw water cooled version. Sorry, can't remember the Halfords Part Number. I just took a genuine Yanmar belt with me and selected one with the same circumference and V angle. - I remember having quite a few out on the shop floor at Halfords near Trowbridge. - Haven't lived there for 5 years so this belt must have lasted at least 5 years to date.
 
tim3057 said:
On the alternator set up question - charging domestic battery (manual selection switch) makes a distinct drag on the engine note - almost as if the current drain makes alternator friction increase. Is this normal?
Click to expand...
I had this problem on a Volvo engine. I replaced an old knackered battery and the problem went away. I've not had to change the belt since.
 
SteveIOW said:
I've had a Yanmar 2GM20 in my boat for the last 18 years. A very good reliable engine but for some reason it used to eat genuine Yanmar belts. Black dust everywhere and they had to be replaced every year or two once all the tensioning adjustment had been used up. Eventually tried a Halfords equivilant with "saw cuts" on the inside the problem disappeared. The current Halfords belt has been on for about 5 years and I can't remember the last time I had to re-tension it.
Click to expand...

Interesting - we have the same, constantly tensioning the belt and black dust everywhere, the belt's lost half its width in 18 months (and not many hours running). Will try Halfords next time. Thanks.
 
i also have the same black dust. When i bought the boat the belt was a toothed type belt that worked great although it did need renewing.

As you do, i bought the genuine yanmar one and straight away had the same black dust, trouble with stretch etc and after 1 season it was shot. I then bought another for last year and it's no better (i really wish i had taken the part number of the non yanmar belt, no dust, very little stretch etc)

it seems to me that that Yanmar belts are next to useless.

Can anyone provide a definitive part number for a 2GM20 (raw) that does not shed dust like a wh*** does knic****

A clean engine bay and the need to not tension the belt every sail would be a miracle
 
tim3057 said:
I'm getting through alternator belts at an alarming rate - what's the principal cause? Too tight? Too loose?
Click to expand...

Jumblie ate one on her way north and started munching another fifteen minutes of running after I fitted it. The cause appears to be an alternator which is seizing - or nearly seizing - when it gets hot.
 
Ruffles and Ubergeekian both valid imo.

Change type of belt as suggested and then have a hard look at the condition of the batteries and then ho hum alternator bearings when hot ( slacken belt and use gloves obviously).

Even on a 30gm you will 'hear' the alt kicking in and out as a definite change in rpm or noise, esp at idle.
 
Another point is that an alternator can almost be a 'constant power' device.
It tries to generate the same current regardless of rpm.
Power=torque x rpm
So more revs means less torque.
If you let the engine idle just after starting, batteries will be drawing most current, so belt forces are biggest.
Give it a few revs if the belt is making any noise! (I'm not saying red-line it!)
Particularly an issue with more modern alts that really want a multi-vee belt with a spring tensioner.

If you measure the outer circumference of the belts in mm, you can order decent ones from places like rswww.com.
 
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