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measuring a pulley

3

37chief

Well-known Member
Location
California
Of all the things in life I have learned, measuring the distance between two pulleys is not one of them. I need to find a belt for my flail mower I bought last year. The belts I removed just don't fit, even though they are the exact ones I removed. The belts have been in the sun for a while. Do they shrink? If there is a belt tensioner how much do I add for that? Stan
 
What I do is take a piece of rope and bring it around the pulleys just like the belt would be and mark where the end meets each other. Then measure how long it is. That tells you the belt length. If the pulley is 1/2 inch use 1/2 inch rope etc.
 
I run baling twine around both pulleys (if you dont have the orig. belt) leaving the string somewhat loose.. mark the string or whatever with marker where they meat..Ive done this a few times with success.. not tight not super loose then compare the string rope or whatever to the inside of belt circle..

rather have the old belt.. sun on belt would make hard and dry out..
 
Belt configuration can be tricky.

First, you'll need to determine the cross section needed. Some pulleys will have the size and cross section on the pulley.

Look at the wear pattern on the pulley. It should not be worn shiny to the bottom of the groove, nor should the sides be worn uneven. If the belt has been slipping or the wrong belt run for a long time, the pulleys may need to be replaced.

Once the correct cross section is determined, depending on the complexity of the belt route, you can try to figure the length mathematically, if a simple configuration, or base a starting point by wrapping a "close to right" belt around, marking the length, measuring the result.

As for the tensioner, if spring loaded, take the spring off, position the idler where you would like it to run, get the measurement.

If an eccentric tensioner, start with it about 1/3 of the way to the tight position, take a measurement there.

Mowers are known for being hard on belts. Once you find the correct size, try to find a Kevlar belt, much better quality.
Belt Info
 
I do something like that also. When I install a new belt I keep the old one for measuring and cut to length if it is not torn up too badly
 
I would think there has to be a way to tension the belt whether it is spring loaded or there is a idler that needs to be loosened has to be something there send pic if you can
 
If they came off it, they should go back on it.
Any chance you are routing them incorrectly?
 
When I wanted a new belt for our Woods belly mower the old one was still on and usable, so I attached a 100 foot tape to the outside. Then with my wife holding light tension on the tape, I rotated the drive sheave until the tape came all the way around. I found a good chart online to compare the od of to belt to size and ordered one, I think a B225, and it fit perfect and runs well.
 
(quoted from post at 14:25:02 12/18/17) Of all the things in life I have learned, measuring the distance between two pulleys is not one of them. I need to find a belt for my flail mower I bought last year. The belts I removed just don't fit, even though they are the exact ones I removed. The belts have been in the sun for a while. Do they shrink? If there is a belt tensioner how much do I add for that? Stan
Click to expand...
In a perfect world you take a measurement buy the belt and be done.
In the real world you will measure the belt then go buy that size along with a belt 2 sizes smaller and 2 sizes bigger , go home , figure out which one you really need then return the others on your next trip to town.

Go ahead and try to prove me wrong, you might get lucky once but in the end what I have suggested generally will be the quickest.
 
I thought they should go back on also. The belts are just pulley to pulley with an idler, I think they just shrunk from being out side in the hot California sun. I want to buy new ones, but want to make sure they will fit. Stan
 
Easy way. Just cut one of your old belts. Warp it around your pulleys. Then measure how much gap between the cut ends. Then measure the cut belt laid out straight. Add the two numbers together and you have the OUTSIDE Circumference of your belt. Then look at a belt chart and see what belt you need.

An example: Length measured is 66 inches. It is a "B" belt. So the Outside Circumference is 66 inches. Belts are sized by the circumference in the middle of the belt. On a "B" belt that is real close to 2" shorter than the outside circumference. So in this example you would need a B64 belt.
 
Ron
I have used this formula for Vee belts a number of times and it works!
(But don?t ask me what happens when a third shaft is added!!)
Regards and happy measuring,
Graham.
FORMULA FOR MEASURING LENGTH OF ?Vee? BELTS BETWEEN TWO SHAFTS.

1.) Add pulley diameters together, and multiply by 1.57 = ?A?.

2.) Multiply shaft centres by 2 = ?B?

For belt measurements in inches:

3.) ?A? + ?B? - 1.2 for ?A? section Belts.

4.) ?A? + ?B? - 1.7 for ?B? section Belts.

For belt measurements in metrics:

5.) ?A? + ?B? - 30 mm for ?A? section Belts.

6.) ?A? + ?B? - 43mm for ?B? section Belts.

This is a letter I emailed to a friend. Hope it works for you. Regards.
 
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