Alternator belt for yanmar 3gm30f

[Propellerhead]

I've searched on this forum and others for info on replacement belts but I'm still not sure about the right belt. The belt that came with the boat was labeled Mitsubishi REMF-6370. There is a spare with the boat with the same markings bit it's wrapped with a tag with the yanmar part number 25132-003700. This all matches some (bit not all) the info I've found in my searches so one would think that I have the right belt.

However, the last belt shed lots of rubber and died after only 50 hours. This time around, I noticed that the new belt doesn't really seem to fit in the alternator pulley (see pic)

I found on one thread that someone is using a 10mm belt from Gates. That is considerably thinner than the belt I have but might be a better fit for the alternator pulley. Can someone confirm that this would work?

[AA3JY]

Been using Gates 9380HD belts for years with my 3GM30 F and high out-put Balmar.

[Propellerhead]

that particular Gates belt is 13mm. The one I was thinking of was 6218mc which is 10mm. Anyone have experience with this belt?

[Copacabana]

I took my old Yanmar belt to an autoparts place and bought a bunch of spares for much less than the Yanmar ones (which are Mitsubishi I think). If I recall correctly, the replacement is an A-36 belt (but take the old one to be sure).

[tkeithlu]

Copacabana has got it right. The belt in the photo is too wide for the job; that alternator (and I think the engine pulley) takes a type A belt. There's no point in paying Yanmar's prices for them - they don't manufacture them. Here's a link to a brief run-down:

https://hvhindustrial.com/blog/common-types-of-v-belts

It's possible that you ate a belt because it was the wrong size, but I recommend that you check the alignment of the alternator pulley to the engine pulleys since that's the most common reason to chew one up.

Good luck with it.

[Propellerhead]

Originally Posted by tkeithlu

Copacabana has got it right. The belt in the photo is too wide for the job; that alternator (and I think the engine pulley) takes a type A belt. There's no point in paying Yanmar's prices for them - they don't manufacture them. Here's a link to a brief run-down:

https://hvhindustrial.com/blog/common-types-of-v-belts

It's possible that you ate a belt because it was the wrong size, but I recommend that you check the alignment of the alternator pulley to the engine pulleys since that's the most common reason to chew one up.

Good luck with it.

That link was very informative. Apparently, the narrowest type A belt is 1/2 inch. I believe that this is what I have and it seems to fit the main and water pump pulleys but, as you can see in the picture, it does not fit the alternator pulley. I'm wondering now if this is just the wrong pulley on the alternator. Maybe I need to visit some junk yards.

[Propellerhead]

Decided to just order this: https://www.amazon.com/dp/B07GHNNRB6...hk_typ_imgToDp

[Scubaseas]

To my eye the alternator pulley looks the wrong width. The water pump looks OK for the belt but the alternator looks sized for a Gates 7xxx series belt. Check with your FLAP store to rent or borrow a laser belt alignment tool. You should also check what belt actually fits you crank and water pump pulleys. You may have to buy a new alternator pulley. Any rebuild shop should have them.

[rgleason]

The belt should not bottom out in the pulley, nor should it be so thick that it rides too high and thus reduces touching surface area.

[crashley]

The belt pictured actually fits the alternator properly but is too narrow for the other pulley
Drive belts drive off the side not the bottom

[ColinIOM]

Hi,
I am a retired time served service engineer and also a sailor and Yacht owner with 3GM30F.
What I have found over the years is there are a two issues re vee belt wear in yachts.
The first is the environment in which they live and work, damp and corrosive plus they sit idle for days sometimes weeks and months where corrosion can get hold in the driving faces of the pulleys.

The second is the poor quality of water pump and sometimes alternator pulleys in particular. Usually the crankshaft pulley are made from good quality steel and sometimes cast iron. The other two pulleys are often made from pressed steel.
Once the corrosion gets hold on the polished driving faces, it just chews through belts at a frightening rate easily spotted due to the black dust everywhere.
Proper belt tension (or lack of) and alignment play their part too but I personally believe poor surfaces on the aforementioned pulleys are the most common problem.

What to do and how to get over it is the question.

Well what I have done is, (after fitting a 120 amp alternator) is to combine the change with a drive belt change to “multi vee” (or serpentine) drive system.
There is a reason almost the entire automotive industry have changed to this type of drive is that of reliability, multi vee belts are far superior and have a much better life span.

It is the simple fact that in the same way flat leather belts of a bygone era were left behind with the invention of Vee belts, I believe that for some applications vee belts should also be left in the past.
There will likely be a number of options for this conversion but I know for certain that Electromax do one (I made my own set of pulleys although alternator pulleys are readily available) and mine have now been running the same belt for 4 years of full live-aboard of summer seasons (we sail in Scotland and now the Baltic sea so come home from October until April, then move back on board full time.
This is not a cheap option but I can say with confidence that provided they are instlled and lined up properly it is a fit and (almost) forget item.

See;
https://electromaax.com/Serpentine-P...e-Pulley-Kits/

Good luck
Colin

[Propellerhead]

I considered a pulley upgrade. Balmar also sells a nice looking serpentine belt kit but it's$450 and I would still have my crappy old AC Delco alternator. I'll suppose I'll have to consider if the new v belt pulley doesn't help.

[ilanortho]

Originally Posted by AA3JY

Been using Gates 9380HD belts for years with my 3GM30 F and high out-put Balmar.

Which Balmor do you have? I want to upgrade on my 30GM30F. Thanks.

[01kiwijohn]

Originally Posted by Propellerhead

I considered a pulley upgrade. Balmar also sells a nice looking serpentine belt kit but it's$450 and I would still have my crappy old AC Delco alternator. I'll suppose I'll have to consider if the new v belt pulley doesn't help.

Technically, that alternator pulley fit is not correct. However, it should still do the job, and not shred itself, driving an alternator of up to 80 amps. More than that, it's marginal.
Does your regulator have a soft start feature? If not, and the batteries are significantly discharged, the belt will be working pretty hard, for a while. Just run it at half throttle for about an hour.
I personally use a NAPA 39" belt, on the same kind of pulley you have, for the past 8 years. Change the belt every 500 hours or so.

[Yellowjacket]

Another issue occurs when owners install high output alternators that require more horsepower without considering belt rating. On my boat, alternators that required 5 hp at max were being driven with V-belts with a 3 hp rating, with predictable results. I replaced V-belt system with serpentine. Solved many problems.