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Old 05-13-2014, 11:51 PM   #1
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2 belts or one?

I have an Amptech 125 alternator. Several professionals on the waterfront in my marina have advised me to put another pulley on the alternator and water pump so I can have 2 belts driving the system. This is almost almost unanimous on the waterfront. The pulley on the alternator was inexpensive at $28. I also had the alternator bench tested while I was at the shop. However I need a pulley machined for the water pump. That's $240. Also, the belts should be matched.

The alternator specialty shop pointed out that people put on smart regulators but many fail to understand the wear and tear with on a single belts on large alternators. My shipwright and mechanic also flagged this issue, as do the commercial fishermen here.

This does not seem to be a common theme with the recreational boaters. I'm curious if others have considered this issue.

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Old 05-14-2014, 12:49 AM   #2
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Is the WP capable in its design in taking two belts? Ask Jabsco or Johnson or Sherwood. The issue I have seen is wider sheaves can require stouter pump bushings - meaning a beefier pump. Also, the drive sheave is more an issue on some setups as one belt only may not be enough friction.

Is the current one sheave only setup wearing out belts, squealing or dragging? How long has it been set up this way with existing alt and WP? If you say years, maybe too much free advice.

That said , if your alt is 24 volt, I'd go with two at some point.
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Old 05-14-2014, 06:45 AM   #3
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If you do go to the troubble of setting up for 2 belts , after you find the proper size take the effort to order MATCHED belts.

These are usually higher quality and will last longer.

For a weekend or local cruiser boat 1 belt will prove fine , IF its a no sweat to replace.

For long voyages thru Unobtainum Land the added service life of dual belts would be worth the effort.

Installing mechanical >engine driven< refrigeration is about a 10HP load and dual belts were always far less maint.

At times it is possible to use a 2 belt setup where the belts take different loads , drive different items ,.

IF both are from the same diameter crank pulley and go over the same alt or compressor pulley it works fine , although setting belt tension will need different locations.

IF you are going to all this hassle a 2 inch clutched Jabsco belt driven bilge pump might be a nice addition.
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Old 05-14-2014, 07:13 AM   #4
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Our boat has twin alternators and funnily enough one alternator has one belt and the other two. Neither seems to be hard on belts for recreational use. If I were going to take the time and money to upgrade I would likely look at the serpentine belt conversion kits available.
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Old 05-14-2014, 07:38 AM   #5
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You can also just go with one belt, but limit the output via the regulator's load manager. Limit to say 75% or something like that to keep it under 100 amps.
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Old 05-14-2014, 08:20 AM   #6
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You can also just go with one belt, but limit the output via the regulator's load manager. Limit to say 75% or something like that to keep it under 100 amps.
Yup, but you may not have to limit or change anything. We have 2 single belt alternators. One is 130 amp (house) and the other is 120 amps (engine). The house alternator full on, only puts out 100 amps. The house alternator has a 2.5" pulley driven off the front of a FL SP135. This past winter I had both rebuilt when the house alternator was starting to get a little noisy (bearings), after 2368 hours. New brushes, bearings and bench tested for $50/each. One bely has worked for us.
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Old 05-14-2014, 10:25 AM   #7
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Sunchaser: I remember that discussion about that very issue with the WP with Bob Smith during his FL workshop. The mechanic has worked on a lot of these engines and didn't seem to be concerned the additional stress on the WP. My WP is the same as shown in Larry's photo so the second shive (if that is the correct term) would still be inside and the existing perimeter of the WP housing and should not put additional torque on the WP axel. There is wear on the existing belt, with black dust on surfaces below it. The mechanic felt the incorrect belt was on it and stressed the need for a matched set.
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Old 05-14-2014, 10:47 AM   #8
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Is the single belt wearing fast or slipping? 100A is not that large an alternator.

If not wearing or slipping, stick with one.

Twin belts can be a PITA as any misalignment or difference in groove diameter or difference in belt dimensions can cause the two belts to "fight" each other, and actually increase wear and trouble.

I've actually solved some problems by removing one of the two belts, of course only when load permitted.
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Old 05-14-2014, 10:53 AM   #9
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Depends on the load/tension. The Eagle has one on a water pump, and alternator as there is much load/tension. However the 5K cruise gen set has two heavy duty belts and they due squeal when the electric clutch is engaged. The hydraulic bow thruster is set up for to, but I took one off as I want the belts to be the safety/sacrifice. I carry spare belts for all, routinely check/inspect and ever 5 years replace.

True story.

Many years ago we where going over the pass and a lady with a daughter was pulled over because the car over heated. So I pulled over as it one of the areas we stopped to let the kids run around. Any we had extra water, but no fan belt. So I told the lady I could fix her car but is was going to cost her a pair of panty hose. She was to not sure but she gave me a pair that I cut the lets off and made a temporary fan belt out of them which got her 10 miles to the next town. So guys make sure you have a pair of panty hose in your tool box!
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Old 05-14-2014, 12:06 PM   #10
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100 A is not a big part, the best ( but expensive) solution are a twice bandet belt- this can work without many tension, many tension are bad for the pump and alternator axle.
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Old 05-15-2014, 07:00 AM   #11
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The problem with belt slipping on an alt is NOT belt wear.

The belt slips on the alt pulley and HEATS it up.

Eventually it can get warm enough to melt the grease in the alt bearing , which then runs dry.

Then it usually freezes , and the water pump no longer turns,,,,,

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Old 05-15-2014, 07:14 AM   #12
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For what it's worth, my Volvo TAMD41 P has two belts. It came that way.

You might be able to purchase stock pulleys and not have to have them made.
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Old 05-15-2014, 08:07 AM   #13
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You might be able to purchase stock pulleys and not have to have them made.

I would look for used , if Volvo sells them it would be cheaper to have NASA build a set.
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Old 05-15-2014, 02:12 PM   #14
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You might be able to purchase stock pulleys and not have to them made....
Jim: If you do go with dual belts, it looks like Bomac Marine sells the water pump pulley for your FL.

Bomac Marine- Ford Lehman Engines Parts, Remanufacture and Service
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Old 05-15-2014, 09:39 PM   #15
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Back in the early 90's I put an inverter and high amp alternator on my 351 cu in Ford repowered Trojan. I did it as a learning experiment to save the expense of a generator to run my microwave and coffee pot and other AC stuff. My alternator was a 150A Powerline that came with a two grove pulley. My engine had two groove pulleys on the crank and water pump but the pulleys were a groove off to run the alternator. I couldn't afford to hire someone to 'fix' that so I ended up with a single belt. It worked OK so long as the batteries were not too deeply discharged. When they were the belt would 'squeak' a bit. I ended up replacing the belt every 50 hours or so and the engine would get covered by black dust (belt). If I re-tensioned the belt every few days of cruising it worked OK. I carried two spares. After a 'couple' of years (5), I realized I could make spacers for the pulleys that were off center. I did that for almost no expense and had no dust or need to re-tension for a full season of use. Why did it take that long. I also come to learn that the need to buy matched belts wasn't required so as long as I bought high quality (Goodyear) belts. The high quality belts are held to a tighter length tolerance. I never had dust or issues for the next 15 years of running it. Bite the bullet and install dual belts, or convert to a serpentine flat belt. It's worth it.
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Old 05-16-2014, 11:09 AM   #16
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Thanks Larry. I've already gone done the road of having one machined for me. It's ready and I will pick it up today. This has been an interesting thread and shows a definite dichotomy of opinion. :-). My one belt system definitely produced dust and my mechanic said the belt was incorrect for the pulleys in place.

The pulleys turn as a result of friction of the belt surface on the pulleys. This from the combination of belt tension and belt surface area. If the belt surface area is doubled (2 belts), you should in theory be able to turn the pulleys with less belt tension, reducing pressure on the bearing surfaces. Once installed, I will monitor closely.
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Old 05-16-2014, 12:16 PM   #17
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I run a hydraulic thruster off a double belt/pulley. I use a (supposedly) matched industrial set. Haven't had to re-tension in several years, and I do check it often. You won't have any problems.
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