Bunton V-belt Sizing

Animal Mother · Jun 21, 2013

I recently purchased a Bunton 48in Walk Behind. I am having a very difficult time finding a replacement engine to deck belt. I placed an order with Lawn Mower Parts, however they informed me that the belt is on back-order. I have listed the part number and mower information below. I am mainly just trying to find the v-belt dimensions, so far I haven't located a cross reference for this belt.

Bunton Gear Drive 48 (634403)

Engine to Blade Belt (PL9065)

chance123 · Jun 21, 2013

I believe I have those size/dimensions/cross reference and will post later

Animal Mother · Jun 21, 2013

Thank you chance, I appreciate it.

impalass · Jun 21, 2013

Animal Mother said:
I recently purchased a Bunton 48in Walk Behind. I am having a very difficult time finding a replacement engine to deck belt. I placed an order with Lawn Mower Parts, however they informed me that the belt is on back-order. I have listed the part number and mower information below. I am mainly just trying to find the v-belt dimensions, so far I haven't located a cross reference for this belt.

Bunton Gear Drive 48 (634403)

Engine to Blade Belt (PL9065)

Belt Length Formula
Pulley A x 1.57
+ Pulley B x 1.57
+ Distance between shafts x 2 +1
= Belt Length

Belt Length = 2C + 1.57 x (D1 + D2) + 1-in.

Where:
C = The distance between the motor and fan shafts
D1 = The diameter of the small pulley
D2 = The diameter of the large pulley

The math is quite easy; it simply includes adding and multiplying. Here is a completed formula to walk you through the steps.

Example:
C = (12-in.) distance between shafts
D1 = (3-in.) diameter of the small pulley
D2 = (8-in.) diameter of the large pulley
New belt length = 2C + 1.57 x (D1 + D2) + 1-in.
2(12-in.) + 1.57 x ( 3"+ 8" ) + 1-in.
24-in. + (1.57 x 11-in.) + 1-in.
24-in. + 17.27-in. + 1-in. = 42.27-in.
So, select a new belt the next length above 43 inches.

Buy a belt made with kevlar.

chance123 · Jun 21, 2013

This is very interesting. The PL-9065 is a propritery belt made for Bunton-Goodall. I went through the same thing recently with a "Wright" mower. What I ended up doing is to get a belt that was close in size. Many times the idler pulleys have enough travel to adapt for the change in belt length.
The Bunton as like the Wright machine belts are 1/4" fractional length sizes. If you get a belt that is 1/4" longer (or shorter),from your OEM, it would be the normal 1/2" fractional sizes available at many places. At the best, a commonly available belt would only be 1/4" off in length from the OEM, so the idler should compensate.
The method to their madness is so you can only purchase the belt from them.

Animal Mother · Jun 21, 2013

Thank you for the replies and formulas.

I follow the math needed to calculate belt length, however how over-sized should the belt be to ensure that the deck does not engage when the idler is in the deck off position? For instance, if the pulley calculation yields a 84in belt, should i buy an 86in belt to ensure that it is not grabbing the engine and deck pulleys when the idler is disengaged?

Let me know if I am not explaining this well.

impalass · Jun 21, 2013

Animal Mother said:
Thank you for the replies and formulas.

I follow the math needed to calculate belt length, however how over-sized should the belt be to ensure that the deck does not engage when the idler is in the deck off position? For instance, if the pulley calculation yields a 84in belt, should i buy an 86in belt to ensure that it is not grabbing the engine and deck pulleys when the idler is disengaged?

Let me know if I am not explaining this well.

2 inches is too long and will not stay on buy a belt as close to the calculation as possible.

chance123 · Jun 21, 2013

If you have the old belt, that would be great. One important thing that the formula above doesn't include is "belt width". This determins how deep the belt rides in the pulley groove. I "think" yours is a 5A or 5/8" width. Your old belt should reveal that. Another way you can get a close measurement (if you have the old broken belt), is to tape the broken ends together, and make a mark anywhere on the belt. Then take a tape measure on the outside (the widest part) of the belt, and measure the length from that mark, all the way around the belt and back to that mark. You will probably see that it ends up at ***1/4 or 3/4 depending on the amount of stretch is has. Then if you purchase a belt that is 1/4" shorter than your measurements, it will probably work. Once you try it, you will see if the next size longer would have been better.

impalass · Jun 21, 2013

chance123 said:
If you have the old belt, that would be great. One important thing that the formula above doesn't include is "belt width". This determins how deep the belt rides in the pulley groove. I "think" yours is a 5A or 5/8" width. Your old belt should reveal that. Another way you can get a close measurement (if you have the old broken belt), is to tape the broken ends together, and make a mark anywhere on the belt. Then take a tape measure on the outside (the widest part) of the belt, and measure the length from that mark, all the way around the belt and back to that mark. You will probably see that it ends up at ***1/4 or 3/4 depending on the amount of stretch is has. Then if you purchase a belt that is 1/4" shorter than your measurements, it will probably work. Once you try it, you will see if the next size longer would have been better.

Another way is to use a rope same as the width of the belt and wrap the rope around the pulleys and measure the rope length.

chance123 · Jun 24, 2013

impalass said:
Another way is to use a rope same as the width of the belt and wrap the rope around the pulleys and measure the rope length.

That would work too as long as the rope is not thin as is thick enough to ride high enough in the v of the pulley

Bunton V-belt Sizing

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Animal Mother

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Animal Mother

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Animal Mother

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