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Old 18-10-2019, 10:27   #1
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Serpentine vs dual V belt?

Wasnt sure if this would be better posted in engines or not but here goes. Im looking to improve the setup on our 4JH-DTE which currently has a balmar alternator and single v belt. I believe the alternator is about 100amp but Im planning at some point to upgrade to a higher output say 150amp alternator. I was thinking to convert the belt system now as I need to replace the belt at a minimum so thought why not make the change now.

My gut tells me I would prefer dual V over serpentine but I wondering? Are there any opinions (dangerous question I know) on sepentine vs dual v belt setups and if going dual V can anyone suggest a reputable vendor for the conversion kit? I see the serpentine kits all over the place.
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Old 18-10-2019, 10:56   #2
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Re: Serpentine vs dual V belt?

Serpentine would be superior.
1. Itís a newer and improved tech over dual v.
2. Dual v requires that you find a matched set of belts to evenly share the load. This can range wildly from a theoretical problem to a plainly apparent one
3. Carry one spare belt or two?
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Old 18-10-2019, 11:04   #3
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Re: Serpentine vs dual V belt?

I have a 4JH4E yanmar. Last season put on a Balmar 150 amp alt with serpentine belt. Would never do duel v belts...... serpentine is great. And looks cool too! Balmar makes engine specific kits.......
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Old 18-10-2019, 13:47   #4
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Re: Serpentine vs dual V belt?

I converted my two 4JH4E to serpentine last winter. I did not buy the expensive balmar kit but simply purchased the serpentine parts from Yanmar (4JH5 I think, compatible with 4JH4, may not be compatible with yours) for less than 150EUR. It is 6V belt though, not 8V. It is driving a 200A delco 28SI, no problem so far.


I think the genuine yanmar system is superior to the above picture as it comes with an additional pulley that pushes the belt up to the alt and provides more contact between alt pulley and belt. Also allowed me to use a longer belt and move the alt far away from the engine.
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Old 18-10-2019, 13:58   #5
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Serpentine vs dual V belt?

Nothing at all with dual Vee if you can find the parts.
I donít believe you will find matched belt sets anymore, Iíve heard itís because belt manufacturing is good enough now to not require that anymore. I do not know if that is true or not.
One advantage of a dual Vee is if one breaks, you can turn down or turn off the alternator and still have cooling until you can get to where you can fix it.
I learned to fly a helicopter that the main rotor was driven by V belts, it works and had lots of redundancy.
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Old 18-10-2019, 14:20   #6
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Re: Serpentine vs dual V belt?

Take me tops 10 minutes tops to changed a serpentine belt if broke.
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Old 18-10-2019, 14:53   #7
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Re: Serpentine vs dual V belt?

As far as changing a serpentine or a V is the same.
I just wish these serpentine kits were ďproperĒ serpentine kits as in they had a belt tensioner. Now that would be worth what they cost.
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Old 18-10-2019, 15:31   #8
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Re: Serpentine vs dual V belt?

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Originally Posted by a64pilot View Post
As far as changing a serpentine or a V is the same.
I just wish these serpentine kits were ďproperĒ serpentine kits as in they had a belt tensioner. Now that would be worth what they cost.

I'm going to design a tensioner for our Perkins single V belt alternator drive this sailing season. I have a small home shop back in the USA where I can build something.
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Old 18-10-2019, 17:05   #9
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Re: Serpentine vs dual V belt?

Sounds like a lot of support for the serpentine belt. Do not the larger alternators as in 200amp and up prefer dual v over serpentine?
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Old 18-10-2019, 19:31   #10
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Re: Serpentine vs dual V belt?

Another datapoint to add to your confusion:

We have a Yanmar 4JH4-HTE (turbocharged 110HP) with two 150A@24V ElectroDyne alternators running off it using two V-belts each. This is the equivalent of two 300A alternators at 12V, and they put a noticeable load on the engine when at full output. The two V-belts seem to handle things fine, but matched belts are a must or else you just keep burning up the tighter belt of the two. After much experimentation with different brands/types (and a lot of toasted belts), I finally found Gates Tri-Power belts and they seem to do the trick. They are lasting over 500 hours and tension pretty equally. I believe they go through a more rigorous manufacturing process to ensure closely sized belts.

That said, if I could do things over again I would probably go the serpentine route. The V-belts are never the exact same tension, and I suspect a properly sized serpentine belt would handle the load better and last longer.

Hope this helps...
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Old 18-10-2019, 21:14   #11
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Re: Serpentine vs dual V belt?

I went with 2 V belts to drive my 180 amp at 12 V SI28 only because it was the least expensive way to get the job done. The only part that had to be custom ordered was the water pump pulley. I did make a better tensioner that the old "pry bar it into place and clamp it down" junk that came with the engine.

On farm equipment in the old days we bought "matched sets" of v belts for the bailer. (7 if I remember correctly.) When researching this conversion I couldn't find matched pairs or sets so I called Gates. They said that (as mentioned above) the standard belts off the production line now are closer matches than the hand picked ones of the old days. You do want belts from the industrial line instead of the the cheap belts designed for the $500 riding lawn mowers. I have over a thousand hours on my pair with no issues. Careful alignment is rewarded with either setup but I suspect V belts may be a little more forgiving.

There are several widths and angles of v belts so be sure all your pullies and belts are exact matches.

Having said that, if the cost had been even close I would have gone with the serpentine set up.
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Old 19-10-2019, 11:14   #12
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Re: Serpentine vs dual V belt?

Quote:
Originally Posted by SV Demeter View Post
Wasnt sure if this would be better posted in engines or not but here goes. Im looking to improve the setup on our 4JH-DTE which currently has a balmar alternator and single v belt. I believe the alternator is about 100amp but Im planning at some point to upgrade to a higher output say 150amp alternator. I was thinking to convert the belt system now as I need to replace the belt at a minimum so thought why not make the change now.

My gut tells me I would prefer dual V over serpentine but I wondering? Are there any opinions (dangerous question I know) on sepentine vs dual v belt setups and if going dual V can anyone suggest a reputable vendor for the conversion kit? I see the serpentine kits all over the place.
This is a no-brainer, go with a serpentine belt conversion. I did it on my Volvo Penta D2-55B with a 110V Balmar and it is ever so much better.

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Old 19-10-2019, 12:16   #13
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Re: Serpentine vs dual V belt?

i'm wondering about the additional load on the cooling system pump (not the seawater pump) when adding larger alternators. specifically, will the pump bearings handle the load without degradation. i have seen larger alternators belted to the engine crank directly to avoid this issue.
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Old 19-10-2019, 12:19   #14
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Re: Serpentine vs dual V belt?

Can't speak to serpentine belts, but I have 10 years of experience with dual belts driving a 100 amps x 24v school bus alternator. There's no problem with matching belts, but you need a fair amount of tension which can't be good for the front crankshaft bearing, and it requires frequent adjustment.

I can't say from experience, but serpentine must be better.
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Old 19-10-2019, 12:48   #15
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Serpentine vs dual V belt?

Quote:
Originally Posted by motretu View Post
i'm wondering about the additional load on the cooling system pump (not the seawater pump) when adding larger alternators. specifically, will the pump bearings handle the load without degradation. i have seen larger alternators belted to the engine crank directly to avoid this issue.


The tension from driving higher powered devices whether they be alternators or hydraulic pumps etc does impact the lifespan of a water pump and even possibly the front crankshaft bearing.
However unless taken to the extreme itís within tolerance of the pump and certainly the front crank bearing. Meaning you get thousands of hours out of a water pump and the front crankshaft bearing should never be why you need an overhaul.

What takes side loads to the extreme is trying to extract more power from a belt system that itís capable of by really tightening down on the belt, and many, many people especially with single belts do that, because they have to or the belt slips.
That is why I wish my serpentine belt system came with a spring loaded tensioner that both keep belt tension perfect, and provides more wrap around the driven pulley so that even more power can be extracted with less tension.
Average belt on the average alternator wraps about 1/3 around the alternator pulley, with a tensioner under the alternator itís easy to get that up to 1/2 way around, the more in contact, the greater the friction of course.

Serpentine belt kits for what you get are in my opinion overpriced, but whatís the option?

Average street price for three aluminum pulleys and a belt is $450 or so?

The front crank bearing would be hard to damage from a belt PTO in my opinion, unlikely to happen from an average alternator, again in my opinion.

A toothed drive belt would be better than a serpentine, again in my opinion and for that kind of money Iíd expect one.
There is a bazillion different sized camshaft drive belts, why not drive an alternator and water pump with one?

Belt diagram on my old truck that had a high amp alternator, you can see how much belt wrap there is, the idler pulleys is why.
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