Twin belts

[West star]

I have a Westerbeke, they do not make a serp kit for it. My crank pulley has two belt groves, my water pump has one. If I install a twin groove pulley on my alternator, can I use the belt that goes to the pump, the crank, and the alternator, with a belt that goes from the crank direct to the alternator? I was thinking i could, because belt speed should be the same. However, I also thought the belt may be slowed/slipping because of the water pump in the loop.
Any thoughts?

[Strait Shooter]

I can see where there is room for speculation, but.....

I'd be apt to go ahead and try it and monitor the results. That in the end will bring about the most expedient results.

[a64pilot]

Your problem will be getting good tension on both belts, if you can get that, then you should be fine. Is it possible to source a double pulley for the water pump too, so everything would be driven by the same size belts?

[hellosailor]

West, there are reasons why "everyone" has abandoned twin belts in favor of ribbed belts. Which don't have to be "serpentine" in order to work perfectly well. (Ribbed is the belt type, serpentine is a layout.)

Twin belts were probably most common in heavy duty (police, fire, taxi) automotive fleet use. They were a continual maintenance nightmare, because even if you buy a set of matched belts, they stretch unevenly, they are installed with different tensions, they take the loads unevenly, and then one always snaps leaving you to buy another set. Of matched twin belts, not just two belts of the same part number.

So if you absolutely must...use twin belts. Get a good tensioning tool and try to match them, and keep matching them every couple of weeks. I think you'd do much better in the long run by machining the pulleys to use a ribbed belt instead. Or installing two alternators, opposed to balance the loads on the shaft, each with one belt.

[West star]

I can get a two rib pulley for the water pump, but unrealistically expensive.

[hellosailor]

Any machine shop can make up a custom pulley, but in the US, in metro areas, that's likely to be over $150 for "just" a simple pulley.

[Opie91]

Did you try these guys?

Complete Marine Serpentine Pulley Kits

Not cheap, but it may solve your problem.

[bmm32005]

What model Westerbeke do you have? They make one for the 38B4.

[jcapo]

And use Gates "Green Stripe" belts.

[Cheechako]

Originally Posted by a64pilot

Your problem will be getting good tension on both belts, if you can get that, then you should be fine. Is it possible to source a double pulley for the water pump too, so everything would be driven by the same size belts?

Hit the nail on the head... devise an idler to put tension on the extra belt and all should be good. Almost all cars have a smooth idler on the back of the belt now. Sounds like a trip to the wrecking yard is in order!
Double belts on the water pump could be too much for the bearings in the pump?

[a64pilot]

Hadn't thought about it, but an idler would allow tension adjustment of the additional belt to match the existing one perfectly and solve your problem entirely.
for the people that think you can't do matched drive belts, I learned to fly as all Army aviators of my period in a Hughes 269 helicopter. It's main rotor was driven by I believe at least six matched drive belts and an idler pulley to tighten them, just like a riding lawnmower. As Mickey Mouse as this sounds, it held 200 hp or so for hundreds of hours flawlessly and gave no trouble.
I know sounds like Bull, but don't believe me look up Hughes 269 drive system. You can put enormous amounts of power through V belts if done correctly.

[Cheechako]

I would imagine the heli belts were closely matched and very expensive... but it's a great point... two belts traveling the same route and pulleys etc seem to match themselves quite well. I would imagine the tightest one burns in until the two match well. You used to be able to buy matched sets for critical applications. Not sure any more.

[Tim R.]

Call John at Electromax. I would be very surprised if they do not have a kit for your engine. They are also willing to make a new kit.

Super nice guy and does what it takes to make sure you are satisfied.