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Old 26-10-2010, 18:29   #1
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Installed New Belt in Yanmar 3jh4e

Hello!

I'm wondering if someone can lend me some guidance on how to proceed with replacing the belt on my Yanmar 3jh4e. I loosened the bolts on the alternator, allowing it to tilt inward, and removed the old belt. Then I stretched the new belt on over the three pulleys. Having done so, I can see that the new belt (although it is the same make and model as the old belt) is so much tighter than the belt I just took off that the alternator cannot be tilted away from a rubber hose that runs alongside it.

I'm attaching an annotated diagram from the manual to help describe what I'm seeing.



What I am wondering is:
1. Is it a problem to have the body of the alternator touching this hose?
2. How long should I expect it to take for the new belt to stretch enough for the alternator to be tilted away from the hose?
3. Am I missing something? Ie. should I have "seated" the hose into the pulley notches a bit farther, somehow?

Many thanks,
Will
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Old 26-10-2010, 18:44   #2
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I have a non-Yanmar alternator on my 3QM30, and have gotten burned occasionally -- finding that the marked sizes across brands aren't consistent. You might want to try a somewhat longer belt.

I'm assuming you've used a (gentle) pry (like a piece of 1x2" board) to tension the belt, and the alternator is still touching the hose?

You definitely don't want the alternator touching hoses, since vibration will wear thru them.
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Old 26-10-2010, 18:50   #3
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Check that the belt is properly seated on the pulleys. (If you can arrange temporary clearance for the hose maybe just a one second jab on the starter with your finger on the stop button at the same time) If it is still too tight, you will need a slightly longer belt. When the belt is right, go back and buy a spare. Also it is a good idea to write the belt numbers in the log.
Regards, Richard.
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Old 26-10-2010, 21:41   #4
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I had the same problem on my 3JH. I wrapped the hose with 2-3 layers of electrician's tape to protect it. Worked for me.

David
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Old 26-10-2010, 21:55   #5
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Quote:
Originally Posted by wronco View Post
Hello!




What I am wondering is:
1. Is it a problem to have the body of the alternator touching this hose?

Yes - Eventually it will chafe through

2. How long should I expect it to take for the new belt to stretch enough for the alternator to be tilted away from the hose?

A couple of operating hours.

3. Am I missing something? Ie. should I have "seated" the hose into the pulley notches a bit farther, somehow?

Probably not missing anything. Although you belt is the same part number as removed, is it a Yanmar belt? I am an OEM parts purist. can't help myself.

I would tension the belt, apply chafe protection (tape) to the hose and adjust in 10 hours.

Many thanks,
Will
There are two critical dimensions - total belt length and total belt width. A new belt will be tight but it will seat properly and if nothing else has been disturbed there should be clearance on the alternator.

An aftermarket belt can be slightly different than OEM.
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Old 26-10-2010, 22:08   #6
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It always seems to be rather tight there.......I have seen a number of "homegrown cures" among them a slit piece of hose as protection.

Is the cross-section of your new belt the same as the old?

I have had this drive me nutz when replacing belts on older boats.

Pulley Grooves are not created equally.

If you cannot get to a source of belts easily.....You may be on that remote anchorage (that I hope to be on in a couple of years).....run the engine.....retighten.....you may be surprised on how the belt breaks in.

Do not overtighten the belt. PM me for the "secret" tension test.
That was taught to me by my mentor in the business
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Old 26-10-2010, 22:17   #7
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Sounds like a similar problem I had, even started a thread about it:

Coolant Hose Rests Against New Alternator

Mine was due to putting in a slightly larger alternator. Anyway- the good news is it is a super simple fix- buy a bigger belt.

Another possibility you can do is the mounting bracket arm "thingy" that the alternator top mounting bolt slides on to tighten the belt probably has two holes on it on the other (engine) end. If you are currently using the inboard one switch to the outboard one and that may free up enough space.

Was there a lot of black dust around the alternator? If so maybe your last belt was too tight anyway. But you are using a light pry like the wooden dowel mentioned before (I like my foot), right?

Good luck!

Frank
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Old 28-10-2010, 08:29   #8
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Thank you everyone for your advice! I just want to provide a little update on how we decided to proceed.

The new belt and the old belt, being the same make and model, are (supposedly!) the same size. What I observed, though, is that the new belt is a bit wider and so does not sit as deeply inside the pulleys. I didn't see the old belt when it was new, so I am not sure if it started out the same. Also, on closer examination, the previous owner had wrapped the coolant hose with some kind of heavy tape. If the old belt started out as tight as the new belt, I believe this may have been to prevent chafe.

For now, I took the new belt off and put the old belt back on, tensioning it using the "honey, would you tighten this bolt while I heave on this doohickey?" method. I'm going to proceed by getting a *new* new belt that fits better, and keep the current new belt as a spare.

Thanks again!
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Old 01-08-2014, 03:47   #9
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Re: Installed New Belt in Yanmar 3jh4e

I know this is an old thread but the problem will persist long into the future. We had a slightly different variation of the problem. The original belt had stretched to the point where it could no longer be tightened without hitting the water pump. Cut a long story short, we had a lot of problems with replacing the belt, the solution in the end was extremely simple - buy a good brand AX42 fanbelt from your local spares shop, or buy off ebay, or buy from the many many web shops that will sell you a AX42 or A42. The big advantage for those with different alternators, like us we now have an Electromaax, is you can buy AX42.5, AX43 etc. to go slightly longer if you need to. Price of course is about a third of the genuine Yanmar belt, I now keep several spare belts on board.

AX is the toothed belt, A is a solid belt, think I prefer AX.

Pictures are the 3JH4E using a A42 belt, subsequently changed the AX42
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Old 01-08-2014, 04:53   #10
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Re: Installed New Belt in Yanmar 3jh4e

I will second the advice about only using original Yanmar parts. I have spent my life in the auto industry and believe me, all parts are not created equal! In the case of these belts I have noticed that the Japanese use a different angle on the bolt "V" than the typical Gates/Napa replacement belt. It is not much but is real. I use only Yanmar belts and have never had a failure. They fit properly too, go figure....

Here you can see a Balmar alternator running on a 3jh4e. I believe the pulley on the Balmar is the Gates "V" angle but it has caused no issues in lots of hours.

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Old 01-08-2014, 09:19   #11
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Re: Installed New Belt in Yanmar 3jh4e

Bruce, I see you have a Balmar external regulator connected to the alternator, very similar to our setup. Couple of questions if you don't mind:

- Have you reduced output using the Belt Load Manager on the external regulator
- What Balmar alternator is that, looks like it might be a 60 series, maybe 100 amp.
- How tight have you made the V-Belt to pull the full load on the alternator

We had a few problems with belts under full load when we had a Balmar 60 series 100amp, turned out the alternator was faulty. We decided on a 80amp electromaax as a replacement thinking 100amp or more would be too much for a singe V-Belt. Serpentine conversion would be nice but quite expensive.
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Old 01-08-2014, 15:03   #12
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Re: Installed New Belt in Yanmar 3jh4e

Quote:
Originally Posted by nugeo View Post
Bruce, I see you have a Balmar external regulator connected to the alternator, very similar to our setup. Couple of questions if you don't mind:

- Have you reduced output using the Belt Load Manager on the external regulator
- What Balmar alternator is that, looks like it might be a 60 series, maybe 100 amp.
- How tight have you made the V-Belt to pull the full load on the alternator

We had a few problems with belts under full load when we had a Balmar 60 series 100amp, turned out the alternator was faulty. We decided on a 80amp electromaax as a replacement thinking 100amp or more would be too much for a singe V-Belt. Serpentine conversion would be nice but quite expensive.
First, I do not utilize the regulator's load manager function. I have never had a problem turning a 100 amp alternator.

Second, having spent a lifetime repairing autos, I have developed a pretty good feel for belt tension. Most people grossly under tension belts. It is a fact. Early in my career I purchased a fairly sophisticated belt tension gauge and it fought me a lot about belt tension. This business about 1/2" deflection may have been correct in the days of the Model A but it is woefully inadequate today...
I look for just being able to twist a v-belt about 90 degrees when the belt is tightened.
Make sure you have a correct belt, that everything is free of oil or grease and that pulleys are in good shape. When installed correctly there is no slippage and minimal belt dust. Dust is an indication of wear or slippage. Some dust is normal but a minimal amount. Usually just a bit on the water pump housing after a few hours of run time is all I see.
Bruce
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