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In the Groove: The Best Pulley for your V-Belt

Posted by Crystal Car on 6/12/2018 to Guides
In the Groove: The Best Pulley for your V-Belt
When you’re searching for a general purpose drive or idler, the most difficult and confusing part can be determining how a specific pulley will work with your belt. We don’t want you to get in a situation where you’ve go add suspenders, now do we?

Most of us are not designing machinery to precisely traverse interdimensional portals into alternate realities. Probably.[1]  So an engineering degree is not necessary to pick out most replacement pulleys.

All you really need to know to find an adequate pulley to work with your belt is

1.       What kind of belt are you using? 4L/A, 5L/B, 3L[2]?  Make sure to filter your search results to your belt.

2.       What size is the pulley? Need help with this? Here's how to Measure Your Pulley

3.       How high or low do you want the belt to ride in the groove?

It’s this last one that’s a bit tricky, and the subject of this article.                                                                                 

Before you chuck out your old, busted v-groove pulley, you need to understand where your belt rides in the groove.

Was your belt sitting at the top, maybe with the belt hanging slightly over the flanges of the pulley?

If so, take a look at the Belts that fit information on your pulley’s page. This section is sorted by belt size, so the largest belt is always listed last. Make sure that that your belt size is the last belt listed in the description.  

IF YOU DON’T: When you reassemble your machine, your belt is going to be looser than expected. And then your belt will slip, and you’ll feel like a real loser. Slippage is no joke.[3]

Was your belt sitting around the middle of the groove?

After you’ve narrowed down your options to pulleys that work with your belt, try to choose a pulley that fits *one* of the following attributes

·         Pin Diameter is larger than your belt

o   This will guarantee your belt will not be riding at the top of your pulley, because a bigger pin means a larger belt fit into the groove.

Pin Diameter

Belt Type the Pin is used for






4L/A OR 5L/B





·         Pin Diameter matches your belt, and Overpin Diameter is smaller than Outside Diameter

o   If both are true, then your belt will hit around the middle of the groove

Was your belt touching the center of the pulley?

Then you were probably ripping through belts more often than you’d like[4]. You were also losing a significant amount of power, so no wonder you want a replacement!
The bottom or narrowest part of your belt should never touch the center of a v-groove pulley.  Try getting a pulley with a slightly smaller outside diameter instead of matching the one you have.  


So I did the math, and if a picture speaks a thousand words, what follows will save us all some time.

Here we have a double pulley that works with both 5L and 4L belts:
Notice how high the 5L belt (on the left) sits in the groove. If more than about 1/4 of your belt is showing above the top of the pulley, your belt will not

 4L and 5L in the same pulley4L and 5L belts in the same pulley, side view

Here's an example of what NOT to do: See how the bottom of the belt is touching the center of the pulley? And there are gaps between the belt and the sides? This belt will not work in the pulley, and no amount of tensioning will give good results.
3L belt in a pulley for a 5L belt

Here's an example of a 5L belt in the groove of a 4L pulley. See how much of the belt is visible at the sides? That belt is not contact with enough of the pulley to allow for good power transmission. At the right is a 4L belt in a 4L pulley.
5L belt ins a 4L pulley4L belt in a 4L pulley

Are you feeling a bit more groovy now? I sure am! If not, give us a call at 1-800-776-9315, we love tie-dye around here.


[1] If you are, I recommend looking into [timing pulleys] as they are designed for precision.

[2] What’s the difference between 4L and A, 5L and B? Belts with “L” are designed for fractional horsepower only. A and B belts are more robust

[3] Unless there are bananas involved

[4] Never is always preferred.

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