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Old 17-06-2016, 02:49   #1
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Yanmar 54hp engine. Uprated alternator. Persistent belt slip

We have just bought an Oceanis 42cc 2005. We love the boat but the previous owner has changed the electrics a little. One of the changes was to upgrade the alternator but after three attempts to tighten the belt it is still slipping.

Do I need to just whack it up harder or buy a different belt or buy new pulleys and go for a wider belt? If so is this a standard upgrade on the yanmar and is there a kit I can buy to do this.

The alternator has twin pulleys, the current belt goes through one ( obviously ).

All thoughts appreciated

Andy

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Old 17-06-2016, 04:34   #2
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

How big is the new alternator? You might need double belts. I upgraded to a 210 Amp Balmar and changed out the pulleys to doubles. Gates Green Stripe belts never slipped.
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Old 17-06-2016, 05:10   #3
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Double sheave pulleys for sure.... Larger the output, larger the power requirements. Fact that alternator shipped with double sheave says it all.
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Old 17-06-2016, 06:05   #4
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Cruisero have serpentine belt kits for this type of fix


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Old 17-06-2016, 06:33   #5
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

If the alternator has 2 grooves in the pulley then for sure you need 2 belts. The belts have to be matched in length so be sure you specify when purchasing the belts.

If the previous owner (PO) did not install a double groove pulley on the engine then that was a mistake. The serpentine belt kits are the best solution.

Don't just keep tightening the belt as that will damage bearings and cause lots of grief. A temporary solution is to turn on the belt manager feature of the external regulator. Assuming it has an external regulator. That should work until you get new pulleys or a serpentine kit.
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Old 17-06-2016, 09:24   #6
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Modifying for two belts or serpentine for sure is the best, but if you haven't tried a toothed type single belt it might help a lot and it's very easy compared to the other solutions suggested. After wearing out bearings on water pumps on my engine and on generator, I switched to toothed belts and was able to considerably reduce belt tension and still avoid belt slippage.

Folks may argue that the toothed belt has shorter life - I haven't seen any problems after about 10 years of using them.

This might not help with the alternator belt - but I just suggest it as a short term fix if nothing else.

Doug
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Old 17-06-2016, 09:43   #7
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Quote: "The alternator has twin pulleys, the current belt goes through one ( obviously )."

Nothing wrong with your engine, nothing wrong with your alternator. The problem is that the one existing belt is physically unable to transmit enuff power when your alternator reaches a certain output.

But why would it reach an output so high that one belt cannot transmit the power now, while it presumably could when the boat came from the factory and the OEM alternator was still on the engine?

Did the PO try to fix something he hadn't understood, and then give up when the "fix" didn't work?

Do NOT "whack it up harder". that would wreck your bearings and mounts. Figure out why the alternator is needing to put out more power than the belt can transmit. The answer will lie in the "draw" that is on the alternator, i.e. how much juice you are gobbling up by your manner of using the boat.

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Old 17-06-2016, 10:01   #8
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

-Is the engine pulley double also? If not maybe the installation was never completed properly.
-Did it perform ok when you tested the boat? Maybe it's fine after the boat sits at the dock on the charger and you start the engine. not fine when it doesn't sit at the dock and the kicks into high capacity
-I've not seen matched belts available for years, but maybe there are. According to the guy last time I asked they are all precision now, and one will wear until they match quickly.

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Old 17-06-2016, 10:07   #9
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Quote:
Originally Posted by Hud3 View Post
How big is the new alternator? You might need double belts. I upgraded to a 210 Amp Balmar and changed out the pulleys to doubles. Gates Green Stripe belts never slipped.
===

Absolutely right. I have a 320 amp fire truck alternator driven by three Gates Green Stripe belts with no slippage at all. As a general rule you need one belt for every 100 amps or so. A serpentine belt would work also. If all else fails you could go to an alternator sheave with a larger diameter. That would give you more contact area and somewhat lessen the power requirement of the alternator albeit with reduced output.
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Old 17-06-2016, 10:13   #10
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

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Originally Posted by waterman46 View Post
Modifying for two belts or serpentine for sure is the best, but if you haven't tried a toothed type single belt it might help a lot and it's very easy compared to the other solutions suggested. After wearing out bearings on water pumps on my engine and on generator, I switched to toothed belts and was able to considerably reduce belt tension and still avoid belt slippage.

Folks may argue that the toothed belt has shorter life - I haven't seen any problems after about 10 years of using them.

This might not help with the alternator belt - but I just suggest it as a short term fix if nothing else.

Doug
DITTO! waterman46
exactly what I was going to suggest. I have had the same experience with a 90amp on my Yanmar. haven't had to switch to double pulleys. The toothed belts don't slip and last longer then the solid belts in my case.
cheers!
JIm
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Old 17-06-2016, 11:37   #11
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

80 amps is about all you should do with a single 3/8" drive belt. You may get 100Amp but with shorter belt life.
Otherwise, double up, or serpentine (my preference)
Do NOT, over-tighten belt to try and reduce slip. You'll put too much load on the water pump bearings, thus leading to yet other problems .
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Old 17-06-2016, 12:11   #12
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

very funny

Serpentine is a 7/900us$ package

1/2" belt,, if it is 3/8"

2x better than 1
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Old 17-06-2016, 14:08   #13
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

Larger than stock alternators can pull 10 -13 HP from your 54HP Yanmar when under heavy load. First, determine what is creating the load. It could be a combo of refrigeration and air conditioning trying to run on old house batteries. Previous posts are absolutely correct in support of double or serpentine belts for alternators producing more than 80+ amps. Also, the load on the forward crankshaft bearing is excessive with only a single belt. The cheapest way to go is to add a double sheave pulley to the crankshaft and water pump and add two new vee belts. Serpentine are more expensive but offer greater reliability with minimal maintenance.
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Old 17-06-2016, 16:26   #14
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

-I found with a 100 amp alternator on a Kubota 6hp diesel motor that it had plenty of HP to do the job.
- A 100 amp alternator on a Yanmar I had, it would slip and squeal all the time with a single belt. That was with an Ample power regulator. Strangely, putting a Balmar series 3 regulator on solved the problem. Lower output with that regulator.
-So a curious question, does a double belt really put more load on the crankshaft bearing? It seems like one belt or two, if they are only tight enough to work the force would be equal...?
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Old 17-06-2016, 17:53   #15
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Re: Yanmar 54hp engine. Uprated alternator. Persistent belt slip

While the suggestions about double belts or serpentine belt are correct, neither solution is easy or inexpensive. On our previous boat, I solved a similar problem by regular applications of "belt-grip", which is a spray-can applied goo that considerably increases the power that a v-belt will transmit sans slippage. In your situation, I'd try that first.

For scaling, our application was a leece-nevile (sp?) 150 amp alternator and a single 1/2 inch belt. The diameter of the alternator pulley was quit small (ttempting to get alternator speeds up) and it would start slipping at around 90 amps. After application of the goo, it would deliver 120 (our max acceptance rate) without audible slippage. No known side effects over quite a few years heavy cruising usage.

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