Yanmar 2GM20 Alternator Belt Problem

[pip50]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust. I have taken all the parts off and cleaned the pulley, replaced the lock nut and fitted a new belt, another two hours and its beginging to loosen again. I spoke with a Yanmar dealer and he said oh no not that again, I'am alwys being asked about that - great help, so if its a known problem anyone else had the same and if so have you found a solution, the dealer did say you could try a toothed belt?

 

[pvb]

Your post isn't exactly clear. Are you saying the belt stretches? Or are you saying the alternator slips on the adjusting arm?

 

[pip50]

The first time it aws the bracket so I thought that was the problem, the new belt is now loose after two hours use and the bracket is tight, I have not removed the new belt yet to check it

 

[steve28]

If the adjustment arm is slipping then it needs a washer under the 12mm bolt and then a lock nut on the other side once the main 12mm bolt is done up.
I fitted one of sterlings new alternator boosters which for some reason has almost totaly eliminated the belt dust i used to get from yanmar belts. By now the belt is usually down past the level of the crank pulley but its still proud.

 

[pvb]

The first time it aws the bracket so I thought that was the problem, the new belt is now loose after two hours use and the bracket is tight, I have not removed the new belt yet to check it

OK, you need to check:-
* pulley alignment (put a straight-edge across the pulleys to make sure they line up)
* pulley condition (clean rust off)
* correct belt width (most important)
* correct belt tension

Using the best quality notched belt you can find may help, failing that you might start with a genuine Yanmar belt.

 

[earlybird]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust.

Your mention of black dust suggests that you are saying that the belt wears rapidly.
I had this problem on my last boat, a 2GM20 engine, a belt would only last a few hours, I suffered this for a full season before realising that the cause was corrosion in the vee of the crankshaft pulley.
The cure involved spending an hour with emery cloth and suitably shaped bits of wood. After that belt wear was a thing of the past,(almost ! )
There are other possibilities of course, such as pulley misalignment.

 

[ShaunG]

I too am in the same situation. All advice above carried out, clean and aligned pulleys etc.

There was a post on this a couple of weeks ago and the outcome seemed to be that the Yanmar belts are not great.

This holds up for me, when i got the boat i had a non genuine belt, no dust and always tight.

3 seasons later and after 8 shredded yanmar belts i have tried everything, the pulleys and alignment are perfect ( i mean really really good, you could eat your dinner of the pulleys and they are inline to within .006 of a mm altough prior to adjustment the alignment was more than good enough, better than any of our cars anyway)

I am now on the hunt for a non yanmar belt, i wish i had taken a not of the original before i threw it.

You are not alone with this problem, i think the belts are at fault, not anything else

 

[dukes4monny]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust. I have taken all the parts off and cleaned the pulley, replaced the lock nut and fitted a new belt, another two hours and its beginging to loosen again. I spoke with a Yanmar dealer and he said oh no not that again, I'am alwys being asked about that - great help, so if its a known problem anyone else had the same and if so have you found a solution, the dealer did say you could try a toothed belt?

I have a similar problem with mine and I'm guessing that it is due to the wrong type of belt being used..........
Mine is marked up as 'Mitsubishi' (as is the spare) but I seem to remember reading somewhere (on these fora I think) that you must use the correct Yanmar belt as it has a slightly different profile. If I recall, the top of my belt sits about flush with the top of the pulley(s), but it should be below the top
I don't use mine much so it hasn't worried me, but when I fit the spare I shall purchase a Yanmar original to replace it.

Found it: http://www.ybw.com/forums/showthread.php?t=235525&highlight=gm20+belt

 

[charles_reed]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust. I have taken all the parts off and cleaned the pulley, replaced the lock nut and fitted a new belt, another two hours and its beginging to loosen again. I spoke with a Yanmar dealer and he said oh no not that again, I'am alwys being asked about that - great help, so if its a known problem anyone else had the same and if so have you found a solution, the dealer did say you could try a toothed belt?

I had the same problem with the original Hitachi generator on my old 2GM20.

It was cured by replacing the old pressed pulley on the Hitachi, with a proper machined one, and refusing to buy any more Yanmar belts - replacing them with a heavy duty serrated one - cheapest was the Quinton Hazell one.

 

[MrCramp]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust. ......the dealer did say you could try a toothed belt?

This is a known problem that has been repeatedly mentioned on this forum for the last 10 years (ish) that I have owned a Yanmar 2GM20.

1. Clean the pulleys
2. Put washers on the locking bolt.
3. Only used decent toothed belts (not the cheapest you can find).
4. DO NOT use Yanmar belts.

 

[Spyro]

Had the same problem, I was continually having to tighten the belt but it would become loose and screach on start up. Cleaned the alternator pully by pushing in a bit of sand paper while it was running (kept fingers well out of the way) Replaced with a toothed belt from the autoshop which cost about £3. Can't remeber which type or size but I have the info on the boat. I've done at least 20hrs motoring since then and I haven't needed to adjust it. At that price if it lasts a season I'll be happy.

 

[dehlerdave]

I too have suffered with this and tried all of the above, even replacing with a toothed belt did not fully cure the problem. A local engineer said that this problem is worse as your batteries age, to quote him "it is a sure sign that your batteries need replacing".
To be fair my battery capacity had reduced considerably.

Two new house batteries and the problem as gone away for now so there may have been something in what he said. I also have an ADVERC which exacerbates the problem when starting the engine as the alternator is on full load.

 

[pvb]

I also have an ADVERC which exacerbates the problem when starting the engine as the alternator is on full load.

No, the Adverc doesn't start boosting until the battery voltage has reached a certain level (around 13.6v I think). This is to prevent excess loading on a cold belt.

 

[Cloven]

This is a well known problem for all the Yanmar GM series engines.

We have solved the problem by using a Gates toothed belt. They are easily obtainable for most motor factors and are much cheaper than the "Yanmar" belt (actually made by Mitsubishi).

The belt is use for my 2GM20F (freshwater cooled engine) is the Gates Extra Service No 6469 EXL AVX 13x975 La

The 13x975 refers to the width & length in mm. If you have the raw water cooled 2GM20, then the length will be different.

Hope this helps.

 

[vyv_cox]

This is a well known problem for all the Yanmar GM series engines.

My 3GM30 must be unique, then The original alternator and water pump belts were replaced after 1500 hours of trouble-free service. They were still working but had internal cracks so I thought it safer to replace them. The replacements were Yanmar ones, now done 350 hours with no problems at all.

 

[pip50]

Thanks to all for your advise all really usfull now its off to Halfords and then to the boat to try out all your advise and tips
P.

 

[MrCramp]

Thanks to all for your advise all really usfull now its off to Halfords and then to the boat to try out all your advise and tips
P.

I wouldn't be going to Halfords as the numpties there will sell you anything. Better going to a decent motor factors. Gates belts are a good as you will get.

 

[pip50]

Halfords a waste of time, what type of car sir? oh a boat we don't do boats, would not even let me look through the shelves as they were packed ( loose sleeve) so must not open.!
Went to Fenner, they measured my original and new Yanmar and are ordering me a toothed version, interestingly they said that the Yanmar belt and its new and has never been fitted was not the size it said it was on the label and was out by 20mm. Hopefully this will help will also go to my local auto spares and see what they have.

 

[petlan]

The alternator belt on my Yanmar comes loose after a couple of hours use. There is also a a significant amount of belt dust. I have taken all the parts off and cleaned the pulley, replaced the lock nut and fitted a new belt, another two hours and its beginging to loosen again. I spoke with a Yanmar dealer and he said oh no not that again, I'am alwys being asked about that - great help, so if its a known problem anyone else had the same and if so have you found a solution, the dealer did say you could try a toothed belt?

I had the same problem with Merc 636's. Solved by using American notched belts. I believe they were called red stripe. Anyhow, you need high quality, high temperature notched belts. Before replacing we were getting through a balt evry 20 hours running. The Sterling makes the problem worse because it imposes heaver loads for longer. If you contact Charles Sterling, I have no doubt he will advise on the most suitable belt for a Yanmar. They are very helpful people.