2GM20F Belts

[KevO]

Sorry, I know this has been discussed several times on here but there seems to be a variety of answers that just don't match up

I have a 2GM20F with an upgraded Hitachi 55 alternator. The Yanmar parts list states the correct belt is part no Yanmar 25132-003700. It currently has a yard-fitted REMF 6370 V belt (Mitsuboshi M-31?) which despite being adjusted correctly, still gives off more black dust than I would expect even though alignment is correct and pulley wheels are in good nick and tension checked appropriately.

I want to replace it with a better quality one (and avoid the stupid Yanmar price hike) and I am steering towards a Gates Green Stripe cogged one but I seem to be unable to choose exactly the right one. Some say Gates 6218MC (950x10), others say Gates 6469 EXL AVX (975 x 13) etc etc etc. Every equivalency site I go to check keeps giving different options and sizes and confusion is setting in Which one do I actually need please?

2GM20F water pump belt is currently a Mitsuboshi M-19. Suggested alternative for this also please?

And the boat is 290 miles away so I cant just whip it off and take it to a dealers until next weekend. Anyone know a Gates stockist in the Falmouth area BTW?

 

[Billjratt]

The pulleys may have been altered when the new alternator was fitted, best to measure them for a correct fit, also the current belt may be wrong -hence the dust.

 

[Georgio]

I would like to know the answer to this also, I get loads of dust from my alternator on the same engine, I *think* it has the same M31 belt you have. The alternator is fitted with a Stirling regulator so I assumed that this was the cause of the dust (because the alternator is made to work a bit harder).

 

[RichardS]

The outer flat surface of the belt should be level with the outer circumference of the pulleys. If the belt is sunken into the pulleys you will get the black dust. My YM belt is 13mm and I think the GM is the same but someone else should confirm this. The ones that were fittted previously were 10 or 11mm and gave me no end of grief.

I bought the Gates 13mm cogged belts for my YM. They are slightly longer than the Yamnar cogged versions as there is not a direct equivalent but they work fine and are easier to get on and still have plenty of adjustment.

Richard

 

[JVL]

Sorry, I know this has been discussed several times on here but there seems to be a variety of answers that just don't match up

I have a 2GM20F with an upgraded Hitachi 55 alternator. The Yanmar parts list states the correct belt is part no Yanmar 25132-003700. It currently has a yard-fitted REMF 6370 V belt (Mitsuboshi M-31?) which despite being adjusted correctly, still gives off more black dust than I would expect even though alignment is correct and pulley wheels are in good nick and tension checked appropriately.

I want to replace it with a better quality one (and avoid the stupid Yanmar price hike) and I am steering towards a Gates Green Stripe cogged one but I seem to be unable to choose exactly the right one. Some say Gates 6218MC (950x10), others say Gates 6469 EXL AVX (975 x 13) etc etc etc. Every equivalency site I go to check keeps giving different options and sizes and confusion is setting in Which one do I actually need please?

2GM20F water pump belt is currently a Mitsuboshi M-19. Suggested alternative for this also please?

And the boat is 290 miles away so I cant just whip it off and take it to a dealers until next weekend. Anyone know a Gates stockist in the Falmouth area BTW?

Your right about the gates belt it solved my problems and I now run a 90 amp alternator off a 2gm unfortunately it's raw water so differs , there is no gates equivalent for the water pump belt

 

[Cloven]

I have a 2GM20F in original factory spec. Belts I use are Gates Extra Service No 6469 EXL AVX 13x975 La (this is toothed belt, 13mm wide, 975mm long) sourced from local motor factors. No idea if these would fit an engine with a different alternator/pulley from the Yanmar original. Used to change belts every season. Current Gates belt has been on now for 6 seasons.

 

[BrianH]

I had a 2GM20 in my last boat with smooth belt - and black dust. I had an unrelated problem and mentioned the dust problem to the mechanic dealing with it. He started the engine with belt off and buffed the inner vee of the pulley wheel surface with emery cloth until it shone. "Keep it lightly oiled" he said. Result, no more dust.

In my case the steel pulley wheel had become microscopically rust pitted, which wore away at the belt. I know there could be other reasons and probably not the case with a toothed belt, but worth bearing in mind for others, as I know the black dust problem on these engines is fairly common.

 

[RichardS]

I had a 2GM20 in my last boat with smooth belt - and black dust. I had an unrelated problem and mentioned the dust problem to the mechanic dealing with it. He started the engine with belt off and buffed the inner vee of the pulley wheel surface with emery cloth until it shone. "Keep it lightly oiled" he said. Result, no more dust.

In my case the steel pulley wheel had become microscopically rust pitted, which wore away at the belt. I know there could be other reasons and probably not the case with a toothed belt, but worth bearing in mind for others, as I know the black dust problem on these engines is fairly common.

I've been tempted to do that but with the belt on so I can do the alternator and water pump pulleys as well. I keep deciding that it's too risky and can see me losing a few fingers. But the idea looks good for the crankshaft pulley.

Richard

 

[BrianH]

I've been tempted to do that but with the belt on so I can do the alternator and water pump pulleys as well. I keep deciding that it's too risky and can see me losing a few fingers. But the idea looks good for the crankshaft pulley.
Richard

It is certainly not something I would have thought of myself, and I flinched at the cavalier way he tackled the job. As for leaving the belt on ... well, you are brave to even think about it. I did not touch the other pulleys, only the crankshaft one appears to be made of steel that supports the less-than-visible pitting.

 

[thalassa]

Mwaah... Did just that with the same engine ... index finger went between pulley and belt... My first thought was... Where did my finger go? But is was still attached, and a bit sore for a day.

 

[Georgio]

I have a 2GM20F in original factory spec. Belts I use are Gates Extra Service No 6469 EXL AVX 13x975 La (this is toothed belt, 13mm wide, 975mm long) sourced from local motor factors. No idea if these would fit an engine with a different alternator/pulley from the Yanmar original. Used to change belts every season. Current Gates belt has been on now for 6 seasons.

Thanks, local motor factor is getting one in for me this afternoon. £11.34 inc vat.