Yanmar 2GM20 eats fanbelts

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Sidedrum

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Help please! My new to me last year boat has a Yanmar 2GM20. The boat came with a generous amount of spares including a couple of Yanmar-labelled fanbelts. Part-way through last year I noticed the fanbelt was squealing on start up, and there was a lot of black dust around the front of the engine. I tightened the fanbelt but it was squealing again very soon after so I replaced it with one of the spares. Same thing happened, with an excessive amount of black dust. The grooves the belt sits in feel pretty smooth, so I don't think there's a cause for excessiver wear there. The fanbelts are untoothed, whereas on my last boat I always used toothed belts - does this make a difference? Or is there some cause for rapid wear I need to track down - and if so, what should I look for?

Any suggestions will be gratefully received.
 
Apart from tension i.e. the correct amount and alignment, the cause of belt dust on my 3GM30 was rust and pitted paint/**** in the pulley grooves on the alternator and engine. I ran the engine without belt for a few minutes holding some emery paper in the groove DON@T DO THAT - IT IS VERY EASY to do yourself some damage!! So take your time and sand/clean it out manually. Once clean I found that the belts lasted and there was no black dust.

Hope that helps.
 
This may or may not be helpful, but I had a similar problem with my 1GM. I had always assumed that the 1GM and 1GM10 were pretty much the same engine in terms of consumables so had ordered a spare belt for the 1GM10. Turns out the 1GM uses a slightly different profile belt. With the correct belt fitted, the problem is solved. Are there slightly different models of the 2GM20?
 
Sidedrum said:
Help please! My new to me last year boat has a Yanmar 2GM20. The boat came with a generous amount of spares including a couple of Yanmar-labelled fanbelts. Part-way through last year I noticed the fanbelt was squealing on start up, and there was a lot of black dust around the front of the engine. I tightened the fanbelt but it was squealing again very soon after so I replaced it with one of the spares. Same thing happened, with an excessive amount of black dust. The grooves the belt sits in feel pretty smooth, so I don't think there's a cause for excessiver wear there. The fanbelts are untoothed, whereas on my last boat I always used toothed belts - does this make a difference? Or is there some cause for rapid wear I need to track down - and if so, what should I look for?
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Check your alternator bearings. When I got my boat she had started eating fanbelts on the delivery trip. It took me a while to discover that the alternator bearings were seizing up when hot, causing the fan belt to slip, and then cooling down in time to be easy to turn when I checked. In your case it sounds as if the bearings may be knackered even with the alternator/engine cold.
 
Try Cogged Raw Edge belts - they transmit more Horse Power than traditional vee/wedge belts. Try a transmission specialist, I always used Fenner years ago but I think they have been absorbed by someone.
 
Totally inadequate belt at eye-watering prices.

I always used a heavy-duty toothed belt on my 2GM which solved the problem - even got to using a 110 amp alternator instead of the 35 amp Hitachi.
From memory it was a 1000mm belt. If you have the original "two-pieces-of-tin" alternator pulley it's worth changing to a proper machined solid pulley. All available @ 20% of Yanmar prices from your local motor factor (but don't use Halfords).
 
If it is corrosion on the pulleys then it is easier to sand the corrosion off if you wrap fine grade emery cloth round the removed belt and pull it back and forth around the pulleys.
 
Oldhairy said:
Are your pulleys properly aligned and parallel ?
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Good question. Many times when the alternator has been removed for some reason the spacers don't go back in the correct position. I agree that the alternator bearings sometimes sieze and cause a problem but more often than not its either pulleys out of alignment or the wrong cross section of belt. Put a straight edge across the pulleys to check and ensure that the new belt engages on the flanks and does not bottom out.
 
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