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Old 29-06-2018, 19:16   #16
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Re: Serpentine Belt advantages

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Originally Posted by rgleason View Post
Good question. I'll hazard a guess. The V depends on tension and friction from driving the belt down into the V, the same forces have to be removed for the belt to become free, thus there is an additional load on the engine.

If a V and a serpentine belt were tensioned on two freely spinning pulleys, which one would be easier to spin? It can't be too much of a difference, but I am pretty sure there is one.


I have a question actually 2.

Is there any belt dust with serpentine?
Is it quieter?
Belt dust happens because:

1. Belt is not aligned correctly.
2. Belt does not match the pulleys.
3. Belt subjected to excessive heat.
4. Pulleys are worn or corroded.
5. Belt size is not correct for the load.
6. Belt is not tensioned correctly.

When my serpentine belt was installed the water pump pulley was 1/2 out of alignment and generating dust. It can happen to any belt. Everyone should have a $30 belt tension gauge and a pulley/belt wear gauge ($10). The worst pulley to use is one of those adjustable types. They are only mean to be used during installation to determine the diameter to be permanently used.
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Old 29-06-2018, 19:19   #17
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Re: Serpentine Belt advantages

I guess I am going to have to get a 1/2" maple dowel, take the belt off and carefully check the alignment on all pulleys!
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Old 29-06-2018, 19:32   #18
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Serpentine Belt advantages

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Originally Posted by rgleason View Post
I guess I am going to have to get a 1/2" maple dowel, take the belt off and carefully check the alignment on all pulleys!


Use a straight edge, like a yard stick, place it on both sides of the pulley and of course it should lay perfectly on the other pulley. Place it on the face of the pulleys.
Even a tiny misalignment is immediately apparent.
Oh and leave the belt on and tensioned, itís possible that it could be pulling things out of alignment, so check with it on.
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Old 29-06-2018, 19:34   #19
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Re: Serpentine Belt advantages

Also comes from too much power/torque required vs the limits of the belt design.

Even if everything is perfect, a load requiring say 5HP is just not going to work off a stock single vee.
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Old 30-06-2018, 02:19   #20
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Re: Serpentine Belt advantages

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The advantage of multi-V belts is that they offer a larger contact area for a given pulley diameter without requiring multiple belts. Every other benefit comes from that.


The "serpentine" feature, where the belt is routed in such a way that the back of the belt is used to drive certain accessories in a reverse direction, is used in automotive applications, but is not ordinarily used in alternator conversions on marine engines.




Can also do with multiple belts. In some cases, there are kits available.




V belts behave badly when overloaded and when run on pulleys that are too small. All the things you list are symptoms of an overloaded belt that has been overtensioned to make it work.


Now, switching from a V belt to a serpentine belt is certainly one way to fix that, and there are kits available, and it's a solution that fits the space easily. That doesn't mean that it is the only possible solution, or the best one for cruising.


The main drawback of multi-v belts is that replacement parts availability is comparatively poor. Compounding this, the alternatives for a temporary repair are also poor. In contrast, you can get v-belts everywhere, and can get by with a v-belt that isn't an exact match, at least for a while.


I would prefer a 2-V or 3-V setup over a serpentine setup, for cruising, for these reasons.


Using undersize alternator pulleys to improve output at idle makes matters worse. A large frame alternator, that will perform better at low speeds, will put fewer demands on the belt drive system overall.


Well I prefer serpentine belts because off all the reasons you mentioned. But I do carry 2 spare belts as they might not be easy to find in remote places.
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Old 30-06-2018, 03:05   #21
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Re: Serpentine Belt advantages

Having worked in the automobile industry through the transition between V belts to serpentine belts and having learned some expensive lessons I would offer the following:
Most people have no concept of just how tight a belt must be to function properly. I certainly did not until I purchased a belt tension gauge.
Many engine manufacturers list belt tensions in service literature and the tools tend to have universal guides for times when the information is absent. I too read the 1/4” to 1/2” rule and when double checked with a gauge it is far too loose.
Even V-belts do not produce much dust when properly adjusted but my preference is for a properly tensioned serpentine belt. Do yourself a favor though, especially if you are retrofitting a serpentine package to a system previously designed for a V belt, beg, borrow or buy a belt gauge before you set tension. You will be surprised and your installation will last far longer with no damage to bearings.

This is the tool I own... https://www.amazon.com/OTC-6673-Univ...+tension+gauge
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Old 30-06-2018, 04:21   #22
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Re: Serpentine Belt advantages

A64pilot and Bruce. Thanks. On this new Yanmar I am still working out the kinks re the alternator belt adjustment. It is a nice tight & solid 3.15" dual foot, but the space and tolerances around the alternator are tight, and the adjustment bracket gives only an inch or so of adjustment. I'm cutting down an expensive balmar adjustment bracket to fit, then the next problem is actually applying the tension required. There just aren't as many leverage points as my old westerbeke.and the last time I bent my screwdriver. I am going to try a pulley pusher device that a friend gave me, but fitting that looks a little tight too. I might have to make my own cheap verson of the "belt buddy".

I will definitely check the alignment as suggested. Maybe 65 amps V does not have to dust.

Do you look at engine specs to determine the required tension? Westerbeke just had the 1/4" belt diagram.
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Old 30-06-2018, 04:38   #23
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Re: Serpentine Belt advantages

I have a Yanmar with a 110 A running on a single belt. I only take out about 60-70A as it is derated. If I apply good tension it is more or less dust free. It is important that tension is checked on a regularly basis. The Yanmar tension device is not really state of the art engineering. There are better tensioners on the market.
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Old 30-06-2018, 04:41   #24
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Re: Serpentine Belt advantages

My 55 h.p. Volvo has a serpentine belt driving a 115 amp alternator into about 450 ah of battery capacity. 600 hours on the engine and the belt hasn't required adjustment yet... And no dust.

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Old 30-06-2018, 04:46   #25
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Re: Serpentine Belt advantages

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My 55 h.p. Volvo has a serpentine belt driving a 115 amp alternator into about 450 ah of battery capacity. 600 hours on the engine and the belt hasn't required adjustment yet... And no dust.



DougR


Can only agree with your observation. My other large frame alternator is running on a serpentine 6V belt and has a proper tensioning device. It is only tensioned when changing the belt.

Anyone who have an opinion on what the upper alternator output is for a 6V serpentine belt?
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Old 30-06-2018, 05:50   #26
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Re: Serpentine Belt advantages

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Originally Posted by rgleason View Post
A64pilot and Bruce. Thanks. On this new Yanmar I am still working out the kinks re the alternator belt adjustment. It is a nice tight & solid 3.15" dual foot, but the space and tolerances around the alternator are tight, and the adjustment bracket gives only an inch or so of adjustment. I'm cutting down an expensive balmar adjustment bracket to fit, then the next problem is actually applying the tension required. There just aren't as many leverage points as my old westerbeke.and the last time I bent my screwdriver. I am going to try a pulley pusher device that a friend gave me, but fitting that looks a little tight too. I might have to make my own cheap verson of the "belt buddy".

I will definitely check the alignment as suggested. Maybe 65 amps V does not have to dust.

Do you look at engine specs to determine the required tension? Westerbeke just had the 1/4" belt diagram.


When I had the single stock 80 amp, all I did was take a piece of oak flooring and use it as a pry bar and tighten the snot out of it. After a few hours Iíd retighten it as they stretch out I guess, then in 50 hours or so When it began making dust, Iíd throw on a new belt.
My battery bank was junk, so it was running hard, a lot.
60 ish amps ought to be well within the limits of a single V. Be sure the belt size is correct, by that I mean the width and angle of the V. This may not be a trueism, but a proper fitting belt should stick up above the pulley, not sit down flush. If too narrow, itís going to slip no matter how tight it is, itís bottoming out
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Old 30-06-2018, 06:13   #27
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Re: Serpentine Belt advantages

Oh thanks for your share. It's so helpful.
I have found this information a lot.
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Old 30-06-2018, 06:55   #28
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Re: Serpentine Belt advantages

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Anyone who have an opinion on what the upper alternator output is for a 6V serpentine belt?
Higher than you'd want to load the engine.

The path of the belt is a major factor.
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Old 30-06-2018, 07:09   #29
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Re: Serpentine Belt advantages

If you look at most automotive serpentine belt set ups, youíll notice the the tensioner pulley is positioned such that it wraps the belt way around the smallest pulley, the alternator.
I havenít seen a boat serpentine pulley set up that does this, we are missing out on a lot of potential drive, but obviously the kits work.
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Old 30-06-2018, 11:49   #30
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Re: Serpentine Belt advantages

There are MANY different forces involved in on-board power generation and this might help some people understand it better.

Transfer of power from the driving sheave (crankshaft pulley) to driven sheave (alternator and water pump sheaves (pulleys) depends on friction between the belt faces and two (or more) sheaves, so the more surface area contact between them, the better. As well, the more pressure between them to limit slippage, the better - within limits. Bigger diameter sheaves, with greater contact area and greater torque capability, will transfer better than smaller diameter ones, but generally there are space limitations and the smallest are cheapest and so they are used.

Also the greater the greater the "wrap-around" of each sheave the better, which is why most automotive serpentine belts travel around idler sheave/s in the opposite direction. This is not usually possible on V-belts. Without this, the total perimeter of the contact area of the whole belt on two or three sheaves cannot exceed 360 degrees, so 120 degrees each on average. This means that, due to physical limitations, some will likely get much less than 120 degrees. As the water pump usually requires the least transfer of power to circulate the cooling water, it would be best if that sheave receives less than the crank and the alternator.

On a V-belt system especially, it would be preferable to have a dedicated belt for the water pump, and a dedicated belt to the alternator, which allows the two sheaves in each case to have an average of 180 degrees of contact, the larger having more and the smaller alternator sheave having (usually) far less, and therefore most slippage occurs there on that tight alternator radius that the belt must travel around. But two separate belts requires a double-groove driver at the crank.

Most of the wear of a v-belt occurs at that small alternator sheave, as the two belt faces are forced to bulge or flex around the sheave faces and so they have difficulty maintaining proper contact. They will also be forced to bulge far more than at the driver sheave so they can never perfectly match the two dissimilar sheaves. Only if the driver and driven sheaves are the same diameter could that occur, and even them not perfectly, as there are transitional stages in the flexing.

Also, the best angle to transfer power of a large diameter sheave is not the same as a smaller diameter sheave, due to more or less distortion of the belt. That is why there are differences in the manufactured angle of belts depending on their application. There is not one standard v-belt angle for all sheaves, even withing the automotive industry!
The radius (and diameter) of the effective transfer of power between belt and sheave is generally regarded as halfway up the side of the belt and that should be slightly higher than about halfway up the sheave face. It certainly is not so low that it will allow the belt to bottom out in the V groove of the sheave, and not so high that the top (outer face) is higher than the sheave face.



This effective diameter of the sheaves can have a marked impact on the speeds of the sheaves. Not so much of a difference on the large driver but a big impact as a percentage change of the driven alternator sheave. But the serpentine belt can also flex around a much smaller diameter sheave, so if you reduce the size of the alternator sheave from say 3" to 2" you have a 50% increase of the speed of the alt. Conversely, if you can increase the diameter of the crank sheave, the belt speed to increase, further increasing the alt speed.

On most boats, the matching surfaces of the contact faces of the belt and sheave will be about 3/8 to 5/8" wide (high) and that is a large surface to have to flex. Compare that to the approx 1/10th inch of contact that each V of a serpentine belt has with its sheave, and you will see that there is a huge reduction of flexing having to take place, and that the overall reduction of contact area is compensated for by having many grooves to do the job. So the belt does transfers power better and wears less as well, producing less dust.

Many people do not know that while some industrial and marine alternators are designed to produce high amps at lower RPM, automotive alternators are not - and that is one of the biggest reasons that those alternators, and their derivatives, when coupled up to a slower diesel with a small driving sheave, burn out. They just do not get enough air through them to keep them cool while struggling to produce higher amps. Automotive alternators are moved by a huge crank sheave of about 8" to 10" diameter and an alternator sheave of about 3" which means an increase in speed of 3 times. When you are in your car doing 3,000 RPM on the freeway, your alt is doing about 9,000 RPM and keeping cool at the low demand asked of it. With my typical, brand-new, Universal M35B marine diesel engine running at 2,000 RPM, my factory supplied automotive alternator(!) was only doing about 3,500 RPM, yet trying to fill those deep-cycle batteries. Yes, I have changed it to a Delco CS144 etc).

It is a very smart idea to make the kits of the "slip-over" driver sheaves to install on the crankshaft of a marine diesel, as not only is it a very simple device to install by bolting onto the front face of the original sheave (no worries about removing the old sheave and dealing with the oil seals) but the diameter jumps by about 20% to 40% - increasing the belt speed, due to the change to a serpentine. The kit should also supply a larger sheave for the water pump so that it does not increase in speed so much that aeration takes place, and so reduces the coolant effectiveness.

So the mystery to me is why do marine engine manufacturers or modifying companies not automatically install larger diameter driving sheaves?

Being an ornery type (my wife tells me) and needing a challenge (I tell her!) I am in the process of machining up my own kit - but I already admit that to do it right is a time-consuming job and it would have been smarter to simply buy the kit. On the other hand, my changes will be custom-made of heavier materials for optimum performance on my particular engine and alternator.

Cheers, RR.
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