General Pulley Question

marq · Oct 18, 2015

I have a MTD walk behind mower that needs the main drive belt replaced, all searching describes it as a B65 belt.

Local mower shop measured the original belt but the size was between a B65 and B66 so took both to trial fit.

B65 was a tight but there was still a little slack to allow the movement of the idler pulley.

B66 was too long as the idler pulley was almost to it's limit (I did not run mower with this belt installed).

So I ran the B65 but noticed the idler pulley was bouncing back and forth a fair amount, I reinstalled the stock belt it moved but not quite as much.

Hoping to avoid a "MTD" replacement belt which is $53!

Questions:

1) Since stock belt appears longer, would that be considered normal with time due to belt stretch?
2) Is movement of the idler pulley considered normal? Assuming it's probably always been there but I'm now looking closer.

davesl708 · Oct 18, 2015

Belt stretch is minimal. There should be a fair amount of adjustment either by spring or threaded adjustment. MTD may well have specified a unique belt size to generate resale.

If the belt slap is not excessive with the B65 and does not slip give it a try.
I get great belt life out of my OEM mower deck and will replace it with OEM when the time comes because of the great lifespan and it fits correctly.

leonz · Oct 18, 2015

ALL V belts are metric. when the V belt is properly tensioned
it should have no more than an 1/8 of an inch of flex in it.

You may want to invest in B65 Kevlar Belt(green thread) at the
Kevlar is much more resistant to shock loading too.

you need to make sure the Pulleys are clean and free of dirt and
the tensioner arm(if it uses them) and the spring can travel
freely as you will have a lot of grass dust in the worst places.
you need to grease the tensioner arm too if it has a grease fitting
several times during the mowing season.

300UGUY · Oct 18, 2015

I was always taught 1/2 inch, but that was on automotive stuff.

Stimw · Oct 19, 2015

If you have the original part number search for it on ebay and make sure it is a Kevlar belt.
I have found replacement belts for under $18. with free shipping!

varmint · Oct 19, 2015

I was thinking about saying what Stimw wrote above. I tried standard replacement V belts for garden tractor uses, and they didn't last very long, compared to the originals. Then I discovered the eBay kevlar belts, cheap, so I gave some a try. So far, so good.