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Old 07-16-2012, 01:41 PM   #1
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Dual Alternator / Crank Pulleys?

We lost an engine yesterday at the most inopportune time because of an overheat situation due to a shredded belt. Anybody here set up a dual pulley system as redundancy?
I know I can get the dual alternator pulleys quite easily but the crank pulleys are another issue.
BTW - These are Ford Lehman 120's and I've already tried American Marine without luck. - Boyd
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Old 07-16-2012, 02:59 PM   #2
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We lost an engine yesterday at the most inopportune time because of an overheat situation due to a shredded belt. Anybody here set up a dual pulley system as redundancy?
I know I can get the dual alternator pulleys quite easily but the crank pulleys are another issue.
BTW - These are Ford Lehman 120's and I've already tried American Marine without luck. - Boyd
You could have a machine shop make one that bolts onto the current pulley.You may even be able to find the right pulley at an equipment shop and just have an adapter/spacer made up.
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Old 07-16-2012, 06:13 PM   #3
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I've seen guys with Lehman's with a spare belt already rigged and secured out of the way so if the operating belt fails, the standby belt can be installed without having to remove interfering parts. I'm sure there are some here who could post a picture of this.
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Old 07-16-2012, 06:31 PM   #4
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Thanks FlyWright, I always keep a spare zip-tied alongside the one in service. Unfortunately mine shredded in a 20 knot wind on our port beam when we were just shy of our slip. We made it in with some creosote skuffs on the hull but no real damage done. Was thinking a true dual setup may offer a little insurance. - Boyd
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Old 07-16-2012, 07:07 PM   #5
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Greetings,
Wouldn't you need a double water pump pulley as well for proper belt tension and not having to carry another sized spare belt?
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Old 07-16-2012, 07:30 PM   #6
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Yup...double crank, alternator and water pump pulleys.
I think I may have found just what I'm after!
Bomac Marine- Ford Lehman Engines Parts, Remanufacture and Service
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Old 07-16-2012, 09:38 PM   #7
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Dual belts are really to carry high loads, not provide redundancy. Very frequently the failed belt will get under the 'good' belt and zip it right off.

Better and cheaper alternative might be to change the belt annually or bi-annually and make certain you use a high quality (Gates) belt, properly tensioned and with pulleys properly aligned.
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Old 07-16-2012, 10:11 PM   #8
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Better and cheaper alternative might be to change the belt annually or bi-annually and make certain you use a high quality (Gates) belt, properly tensioned and with pulleys properly aligned.
My boat has a "C" series Cummins engine with a serpentine belt. I change it every year by replacing with the new one in my spares kit. Changing the belt costs less than $40 and takes less than 15 minutes which includes removing and replacing the belt to the second alternator. Loosing the belt at cruising speed almost guarantees a head gasket job and maybe much more. Cheap insurance!

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Old 07-16-2012, 10:29 PM   #9
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"Very frequently the failed belt will get under the 'good' belt and zip it right off."...That was actually one of my concerns.
The belt was a Gates, it was new last year and was inspected about six hours before this all happened. I have an alternator bracket that I've always had trouble tensioning due to the high output alternator, although I did have it snugged down pretty well before the start of the trip. Guess I'll be taking a closer look at what my options are in that area. Thanks for the advice fellas! - Boyd
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Old 07-16-2012, 10:48 PM   #10
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Boyd, does your HO alternator put out more than 100A on a belt width of 1/2 inch or less? My understanding is that HO alternators over 100A require wider than standard belts, i.e. greater than 1/2 inch or double belts.
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Old 07-16-2012, 10:55 PM   #11
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I know this might not mean much, but my Perkins has a triple-pulley on the crank. One belt runs the water pump and alternator and the other two are for the hydraulic thruster. I think I have the "book" for the pulley I have, and if I think of it next time I am down at the boat, I'll find out who makes it. You may want to ask over at boatdiesel.com. They can't be THAT rare.

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Old 07-16-2012, 11:19 PM   #12
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Boyd, does your HO alternator put out more than 100A on a belt width of 1/2 inch or less? My understanding is that HO alternators over 100A require wider than standard belts, i.e. greater than 1/2 inch or double belts.
Yes, both engines do. They were on the boat when we bought her. Going by memory I don't think the belts are any wider than .5" to possibly .625" This problem has occurred twice, and just on the portside engine.
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Old 07-16-2012, 11:28 PM   #13
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From the Balmar site:

Does belt choice affect alternator performance?
Certainly, belt quality will have a dramatic affect on both alternator performance and the life of the belt itself. We find that high quality belts, such as the Top Cog belt by Dayco or the Green Stripe belt by Gates, will provide the best performance and longest life possible.
Keep in mind, the width of the belt limits that belt's horsepower capacity. As a result, any belt -- no matter what quality it might be -- will fail before its time when the alternator load exceeds the belt's capacity. Once again, if the belt is narrower than 7/16", the maximum amperage load we can safely carry is 80 amps. If the belt is 1/2" wide, 110 amps is our upper limit. Any alternator in excess of 110-amp output will require dual belts, or multi-groove flat belts.


http://www.balmar.net/Page46-faq.html
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Old 07-17-2012, 12:04 AM   #14
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Thanks for that!
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Old 07-17-2012, 06:56 AM   #15
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Sounds like your new Alt bracket is too weak and wobbeling.

Quality is important in belts , go to a US web site and find out the series numbers for the best , and order a set.

Even US mfg have quality grades.

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Old 07-25-2012, 07:03 PM   #16
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You might want to try pm marine diesel in steveston b.c. The owner is paul meyer the number is 604 272 2672. I know they are on holiday but don't know when they are back. No one in the world knows more about ford marine diesels than paul.ron mv welcome dancer
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Old 07-25-2012, 10:17 PM   #17
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There is one on e-bay, item #390435784713.
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Old 07-26-2012, 12:26 AM   #18
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Alignment of the alt and the crank pully is a must, I have machined some spaced wedges to return my Alt to a good alignment, Double belts do tend to get caught up in the other pully and belt if one of them lets go, A standard 65 amp alt running at about 2000 RPM's takes about 12 to 14 Hp to turn it at speed so there are alot of factors in play, Stress, Heat, Wobble and flexing of the Alt bracket under strain, Also make sure the alt if it has been changed had the proper pully on it. so that all the preasure is on the sides of the belt not running on the flat surface of the belt, Good Luck.
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Old 07-26-2012, 07:33 AM   #19
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Alignment of the alt and the crank pully is a must, I have machined some spaced wedges to return my Alt to a good alignment, Double belts do tend to get caught up in the other pully and belt if one of them lets go, A standard 65 amp alt running at about 2000 RPM's takes about 12 to 14 Hp to turn it at speed so there are alot of factors in play, Stress, Heat, Wobble and flexing of the Alt bracket under strain, Also make sure the alt if it has been changed had the proper pully on it. so that all the preasure is on the sides of the belt not running on the flat surface of the belt, Good Luck.
Here are some other inputs I pulled off the web calculatin hp required to turn an alternator...

An alternator typically takes about 1 HP (horse power) for every 25 amps of power generated. So, a 100 amp alternator will require about 4 HP at full output. Most alternators do not operate at full output for very long.

Example:
57A x 14.9V = 849.3 Watts
849.3 Watts / 745.7 = 1.14 HP
1.14 HP x 15% = 0.17 HP
1.14 + 0.17 = 1.31 HP Total

A 12 volt alternator putting out 110 amperes creates 110x12 or 1320 watts. One horsepower is equivalent to 746 watts. 1320 watts equal 1320/746 = 1.77 horsepower.

To that you will have to add an allowance for friction and other inefficiencies.


t's totally a function of the actual output of the generator and it's efficiency. Figure you lose 10% in the belt, and another 10% to friction in the bearings, the efficiency of the alternator/generator. then there is the actually load on the generator....not it's rating maximum output. 1 kilowatt is about 1.34 horsepower. At 12 volts, 100 amps would be 1.2 KW which is about 1 1/2 HP. Add in the efficiency loses and figure about 2 1/2 HP for 100 amps out

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