# Yanmar 3YM30 Alternator Belt



## cyphert (Feb 19, 2002)

When recently replacing the alternator belt on my Yanmar 3YM30 (80 amp alternator) with the same belt that was supplied with the engine new (A 37.5), I had to remove the fresh water pump pulley to fit the belt. The alternator would not swing down far enough to slip the belt over the three pulleys. Yanmar assures me this is the correct belt, but it seems strange to have to change it this way? Anyone else have this problem?


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## JohnRPollard (Mar 26, 2007)

This doesn't sound right. On our 3GM30 engine, it is not necessary to remove the pulley on the fresh water/coolant pump to replace the belt. There is enough throw on the alternator adjustment bracket to slacken the belt completely. Hmmm. 

On the other hand, it sounds like you have a higher amp alternator than standard. Maybe the case is larger, preventing you from getting all the throw from the adjustment bracket. But I haven't heard of folks that have upgraded to larger alternators complaining about this problem.

You might try another brand of belt and see if it makes a difference. I would order some Gates Green Stripe belts, which wear better with the high-output alternators anyway. Good luck!

P.S. I see this is your first post. Welcome aboard!


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## tonic (Jan 22, 2007)

Try calling Mack Boring there a Yanmar distributer 1800 622 5364. Maybe they can put you in the right direction.


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## CrazyRu (May 10, 2007)

NAPA automotive stores have all sort of belts normally for a price lower that Yanmars. The belts made with about half an inch increment, you can buy next size or two sizes bigger.


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## Rockter (Sep 11, 2006)

Sometimes if you loosen the alternator mounting bolts, or take them off so that you can rock the alternator a wee bit, you can get the belt over the alternator puller that way.


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## jason3317 (Dec 20, 2007)

Make sure you loosen the pivot bolt and the swing arm bolt. Sometimes, loosening only the swing arm bolt will not give the full range of motion.


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## TSOJOURNER (Dec 16, 1999)

In your messgae you say "The alternator would not swing down far enough to slip the belt over the three pulleys".
I my 3ym30 I need to use two v-belt, one for the alternator (25131-003000) and another one for the water pump (104511-78780). There is 2 pulley on the crank shaft. May be this could kelp. Good luck,


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## CapnRon47 (Jul 29, 2007)

*Yanmar belts*

My 3GM30 has 3 belts. the inner one is the raw water pump, the next is the water pump and alternator and the outer one is for a Sea-frost compressor.










On mine I have to remove the compressor pulley to take that belt off as the compressor does not rotate much. But the alternator has plenty of swing on its bracket.


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## sorcerer33 (Jun 25, 2007)

How can I find the Gates equivalent fan belt for my Yanmar 4JH2E? I'm going through fan belts fast because my 80 amp alternator is not aligned exactly with the belt. I need the toughest belts I can get until I can get a better alignment.


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## yachtwork (May 9, 2008)

*Belt alignment trick*

A thought on your alignment- A good old trick is to lay a dowel rod into the groove of the pulley. It will find it's own center and give an easy perfect progression of where the pulley is really pointed. This makes it easy to decide on the next step. If that does not help they also make flat belts that replacement the V belt. You can do a search for Yanmar serpentine alternator pulley kit.

Good luck

Scott


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## Stu Jackson (Jul 28, 2001)

sorcerer33 said:


> How can I find the Gates equivalent fan belt for my Yanmar 4JH2E? I'm going through fan belts fast because my 80 amp alternator is not aligned exactly with the belt. I need the toughest belts I can get until I can get a better alignment.


If you can still read the numbers on your existing belt, or can get them from Yanmar or a friend with the same engine, take the numbers into an auto store and they have comp charts.

If that doesn't work, take the belt off and take it with you to the auto store.


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## captflood (Jan 1, 2011)

GREETINGS EARTHLINGS . Looking at your pic. do you haVE THE CORRECT belt V section because it looks like your shredding rubber youi may need to check the sizes and compliance GO SAFE.


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## SloopJonB (Jun 6, 2011)

sorcerer33 said:


> How can I find the Gates equivalent fan belt for my Yanmar 4JH2E? I'm going through fan belts fast because my 80 amp alternator is not aligned exactly with the belt. I need the toughest belts I can get until I can get a better alignment.


Try using cogged belts instead of conventional v-belts. They have "teeth" that make them more flexible so they can transmit power better. Might help with that small misalignment.


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## ereiss (Nov 25, 2002)

*checked the # on my spares*

For my 3ym30 I have cogged belt with the following number on it
129612-42290.

The belt for the water pump is 104511-78780

This all assumes that they gave me the right spares.

Hope this helps.


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