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Old 06-11-2013, 14:56   #1
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Serpentine Belt

I've read stories about oversized alternators damaging engine bearings and seals. How do serpentine belts protect against that? Is it because they reduce the likelihood that the belt gets over tightened to stop slippage?
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Old 06-11-2013, 20:22   #2
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This year I put one on my Perkins 4108. It came with a new water pump with a heavier shaft. 1 season and no issues, almost 700 miles motoring. No belt issues and no dust from the belt.
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Old 06-11-2013, 20:40   #3
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Re: Serpentine Belt

Rusty, they don't. A large alt requires X amount of torque to drive it. Does not matter if it's a V belt, belts, or serpentine, still the same. On a small motor, these loads can cause overloading of the drive pulley bearing, eventually destroying it and the seal. Serpentine belts are cleaner, and also a single belt can (normally) drive a larger ALT than a single V belt.
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Old 06-11-2013, 23:20   #4
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Quote:
Originally Posted by NZ8720 View Post
Rusty, they don't. A large alt requires X amount of torque to drive it. Does not matter if it's a V belt, belts, or serpentine, still the same. On a small motor, these loads can cause overloading of the drive pulley bearing, eventually destroying it and the seal. Serpentine belts are cleaner, and also a single belt can (normally) drive a larger ALT than a single V belt.
But is it the torque that's the issue, or side loading?
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Old 07-11-2013, 00:03   #5
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Re: Serpentine Belt

Its the torque requirement of the apt that causes the side load. One side of the belt is under drive tension, the other side basically unloaded. The load on the belt on the drive side causes the additional load on the shaft bearing. Excess belt tension can also contribute to the problem. If the belt is driven off a crank pulley, there should not be a problem with most engines over about 30hp.
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Old 10-11-2013, 18:28   #6
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Re: Serpentine Belt

I have been planning to switch my 1983 Universal M25 to a serpentine belt. Have a Delco SI12 modified to work with Balmar MaxCharge MC614 and a 150A stator. I have experimented with the settings of the voltage regulator (including the belt saver setting of 4) and I am happy with the performance, except that while cruising I had to replace 3/8"belt too often.To advance this project, I searched for info and came across this dated thread.
Now I haven't done the math and may be way off on this, but my guess is that the individual combustion strokes, as the forward most connecting rod slams down on the journal of the crank shaft every other revolution when motoring or maybe even in fast idle, would impose loads on the front crankshaft bearing that should be comparable to (if not larger than) the loads imposed by the alternator belt. I always figured alternators were traditionally mounted up on the left side (right side facing the pulley) so the belt load subtracts from the operational front bearing loads. Anyone cares to comment?
I have considered adding a ball bearing in front of the crakshaft pulley (M25 has a convenient splined stud poking out there) and preloading it somehow ( spring or short V-belt?) to balance the tension of the alternator belt. Just an (dumb?) idea.
Now the main thing: the commertially available kits are way too expensive for me, slightly cheaper solution were the few machine shops that advertise to make the necessary pulleys from a drawing. The latter, maybe both use aluminum stock, which I don't have enough experience with. Would it wear faster than steel? Any idea about using an automotive pulley that could be modified to fit over the existing V-belt one?
Anyone has done the conversion to the serpentine belt on a small diesel and cares to share details?
Stan
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Old 10-11-2013, 18:32   #7
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Re: Serpentine Belt

I have a serpentine belt on my 160 amp Electromaax Alternator.

The great thing is no slippage, no fan belt dust in the engine compartment and of course a much longer life...
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Old 10-11-2013, 18:36   #8
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Re: Serpentine Belt

Thanks Tom, that's what I am shooting for, no black dust. And if I get few more amps out of it, would be nice too. Stan
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Old 10-11-2013, 19:52   #9
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Re: Serpentine Belt

Check this out: http://www.oceannavigator.com/Septem...go-serpentine/
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Old 10-11-2013, 20:38   #10
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I just ordered a serpentine kit from Electromaax for my Yanmar 2QM15. I'll post impressions when complete.

I didn't really price custom made pulleys by themselves, but my guess is that by the time you fab two or three pulleys (perhaps more than once if something doesn't fit tight) and a couple belts (not to mention the engineering involved) you're not going to be far beyond the cost of a pre-engineered and warranted kit. Might be fun though.
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Old 10-11-2013, 20:41   #11
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Seen this?

http://www.pbase.com/mainecruising/electromaax_kit
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Old 10-11-2013, 21:58   #12
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Re: Serpentine Belt

I've read that the serpentine belts have a higher coefficient of friction than the V-belts do & therefore require less normal force (side load). I have not confirmed this personally.

I have noticed that my current diesel with serpentine belt on 140 amp alternator does not slip, where a previous engine with a V-belt on a 65-amp alternator did screech under heavy electrical loads.

I am currently looking at the possibility of running an alternator off of a timing belt, rather than a serpentine belt, since a timing belt requires even less side load & is far less likely to slip. The timing belt project will require me to make my own sheaves.

Side loading does affect bearing life.

Putting 3 bearings on a single shaft that does not have a flexible joint generally adds more stress to the shaft & bearings in the system than only going with 2 bearings. This is a basic concept from mechanical design 101.
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Old 10-11-2013, 22:12   #13
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Re: Serpentine Belt

Quote:
Originally Posted by Rusty123 View Post
I've read stories about oversized alternators damaging engine bearings and seals. How do serpentine belts protect against that? Is it because they reduce the likelihood that the belt gets over tightened to stop slippage?
No over tightening is still possible. If it is tensioned correctly it's because of the increased contact area in the multiple grooves as opposed to the a single groove. There are 2 side forces on the bearings, the belt pre-tension and active load when pumping water or making electricity. Pre-tension is needed to prevent slippage. The multi-groove belts need less pre-tension for a given active load. Less pretension means less side load on the bearings.
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