Percentage of Pulley in Contact with Belt

[Stevens 47]

I have a Lehman 4D220 engine that I have completely rebuilt, is now ready to crane back into the boat.

My question is in regards to the percentage of the v-belt that will be in contact with the drive pulley. This is the application.

I have constructed a bracket that bolts onto the engine, it is very solid. This bracket has a flat bed with a place to bolt a York refrigeration compressor and an additional (2nd) alternator. Both the compressor and the alternator have 1/2 double v-belts. Does anyone know what the minimum percentage of the engine drive belts that contacts the engine pulley would be needed to prevent belt slippage or failure.

[David M]

Check with the engine manufacturer on this. Sometimes the engineered tolerance is so close that just increasing the alternator output is enough to cause slippage or premature wear.

[DeepFrz]

I couldn't find anything definitive on this but it seems to me that the top of a correctly sized belt should sit at about the level of the pulley flange. It should not be more than about 1/8" proud of the pulley flange. Now that is just from memory, so I would check with the distributor. Calder recommends Gates Green Stripe belts.

Here is part of what it says in Calder's book, paraphrased a bit:

The pulley grooves must be sized so the belt does not bottom out in the pulley. The driving force of the belt must be delivered by the sides of the belt, not the base of the belt. Also the standard industry pulley has a 38 deg. taper to the sides of the groove, whereas many alternators come with 34 or 36 deg. pulleys, which will accelerate belt wear. Replace the pulley with a 38 deg. pulley.

[motion30]

Steve I would guess on the large drive it would be close to 40% Something to consider The water pump bearing is the weak link on these motors Does you drive system include the water pump? I would guess not. American diesel could give you your answer

[delmarrey]

Originally Posted by Stevens 47

Does anyone know what the minimum percentage of the engine drive belts that contacts the engine pulley would be needed to prevent belt slippage or failure.

That's one of those questions that can not be completely answered. It's relative to the circumstance.

As for the wrap of the sheave, it should be around 120º + for most power units. If there is a strong pull like on compressors or hi amp alt's. then 160º + would be better. If that's not enough then a double belt is needed.

But like on some serpentine belts there is a back-side idler/tensioner which gives a belt more wrap as much as 240º.

You'll just have to try it to see for sure. If there is any slippage you'll see a black powder forming around the slipping sheave.



Then there is the positive traction belts.
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[GordMay]

See the “Pulley And Belt Calculator”: Pulley And Belt Information Calculator

And Belts, Tensioners, & Pulleys 101:
http://www.gates.com/common/download...n/428-7174.pdf

[Stevens 47]

Thanks to all for your input

Something to consider The water pump bearing is the weak link on these motors Does you drive system include the water pump? I would guess not. American diesel could give you your answer

Yes the water pump is on a separate pulley v-belt system with a smaller alternator. I agree the water pump bearing is the weak link in the system.

But like on some serpentine belts there is a back-side idler/tensioner which gives a belt more wrap as much as 240º.

The installation of a idler has been a thought, seems that they cause the v-belts to wear faster. What are your opinions on this.

The engine pulley (it bolts onto the original Lehman pulley) in question has 3 grooves. I used Gord's link for the calculator (thanks for that Gord just what the doc ordered). My first thought was to have the second alt and the compressor on the same circuit with a unused 3rd groove. The alt creates the belt adjustment. It looks like the best that I can do is 130 degrees the calculator calls for 165, I would have to install a idler.

The other options would be to run the alt and the compressor on there own separate circuits. The alt with two 1/2" belts and the compressor on the single. The problem would maybe be that the compressor may require 2 belts. The other option is to turn up a 4 groove pulley, placing both loads in opposition. What do you think