When you buy this latest belt, before you lace the belt into the pulleys..............lay a section of the belt into the drive pulley (crank pulley) and sight into the way the belt "meshes" into the pulley groove. Use a good light so you can see clearly. If the very tip of the "vee" on the belt goes to the bottom of the pulley groove......replace the drive pulley, it's worn out.
A vee belt is not intended to touch the bottom of the pulley groove. For the belt to perform as designed, only the sides of the belt vee are supposed to touch the sides of the pulley vee groove. So long as the belt rides up higher than the bottom of the pulley the belt "tenses" itself when under a load, and slippage (and resulting heat/wear) is minimized.
Once the belt pulley wears enough to let the belt touch bottom, it slips more that it pulls.........and there goes your belt.

A fantastic suggestion! I'm embarrassed I didn't think of it... ;) I'm tempted to just buy a new one and throw it on there, but they're $100+...

If I find that the belt is sitting OK in the pulley (and I'll check the hydro v-pulley, too) any other thoughts?

Thanks!

Make ABSOLUTELY sure that all the idler pulleys and tensioner arms and springs are working properly. You might have a V idler pulley where a flat idler pulley should be.

Check any belt guides to make sure they are adjusted correctly and not rubbing the belt.

In many designs engaging the parking brake releases tension on the drive belt. Make sure that linkage is working right.

Only other thoughts I have would include that the leading edge of the deck may be set too low causing an exaggerated belt "angle of approach" between the drive pulley and the deck.
The normally recommended setting of a deck is to have the front edge of the deck about 1/4" lower than the rear edge of the deck.
Another point may be if something in the belt routing corridor on the deck is near where the belt passes and the belt sort of "slaps" this object sometimes, inflicting minor damage that accumulates into a major failure at some point.
Also, what about the "belt keepers" that are supposed to keep the deck belt from jumping off the drive pulley when the belt is slack (disengaged)? Are these pins or bolts in their proper place? Proper setting for them is "close as can be without touching the metal pulley". When set to the proper spacing you should have to gently "pry" the keeper away from the pulley just enough to permit the belt to slip out when you are servicing the belt, and it should "spring back" to that spacing when you stop prying on it.

"Only other thoughts I have would include that the leading edge of the deck may be set too low causing an exaggerated belt "angle of approach" between the drive pulley and the deck".

The aspect of the deck (front to rear) is irrelevant to the MAIN DRIVE belt. It is relevant to the belt driving the mowing deck but that's not the belt the OP is having problems with.

***"The aspect of the deck (front to rear) is irrelevant to the MAIN DRIVE belt"***
Absolutely correct. I suppose I can blame this one on senility. Somehow I missed the point of it being the DRIVE belt for the tranny and I was thinking it was the drive belt to the deck.
Well,...........that's very different. Never mind.
Red faced embarrassment.

Thanks for the tips, keep 'em coming!

I have verified, numerous times, that the belt is routed correctly, with the flat side on flat pulleys and the v-side on v-pulleys. In fact, I've doubted myself so many times that I keep looking at the manual again and again each time... Honestly, if it's done incorrectly then you would end up with the wrong side of the belt touching the wrong pulleys, and it would probably run backwards...

Mownie, I have adjusted all the guards as close as reasonable, and reviewed all of them for brushing. I don't use the brake/"de-clutch" pedal mostly because it's not useful, but I have had the belt pop off a couple times when I did.

About the only thing I can think of, if it's not the belt riding too deep into a v-pulley, is that one of the pulleys is not aligned properly and the edge of the belt is catching the edge of a pulley. But since I don't have a lift all I can do is look at it while lying on my back, and from that perspective it seems fine. I've got half a mind to go ahead and buy a new hydro and crankshaft pulley and see what happens...

Mownie,

We all get a touch of the Mad Cow once in a while... Denny Crane.

Greg,

Since you've installed a different engine...

Did you use the drive pulley off the old engine? If not, a different drive pulley could be for a different belt profile.

Could the drive pulley be riding higher or lower (relative to the drive belt) than it did on the original engine?

Did you verify that the replacement engine mounted exactly as the original engine did and that the drive pulley was at the same height?

Lurker, can't say for sure which pulley I used, that swap was a good 6+ years ago. However, knowing how I work, I simply can't imagine NOT comparing the two and swapping if needed.

The replacement engine bolted exactly in the same place as the prior one. Both are the B&S "Vanguard" twin i/c engines; everything was visually identical except for the horsepower rating (12.5 vs 16).

I do recall looking at the parts manual last night for that pulley, and I did not see a different number based on the engine used. I'll have to look at that in more detail tonight. - GA

Could be that the crankshaft lengths or pulley spacers ot the pulleys differ between the two engines.

You have to make sure that the drive, idler, and transaxle pulleys align before looking elsewhere for the problem.

More info.

After a beer tonight, got underneath the tractor and found the belt stuck in between one of the idler pulleys and its bracket above. The belt came to a screeching halt and, of course, wore off at the crank pulley. Come to remember, it did that last time, too... (he says, foreshadowingly).

Thinking over all the thoughts here, I looked at that particular idler pulley (one of the flat ones where the back of the belt rides, immediately off the crankshaft pulley) and it appeared to be worn more at the top than the bottom, toward its bracket. I messed around with it further and noticed that its bracket -- a bellcrank that has another pulley that controls the tension when the brake/de-clutch pedal is released -- was wobbly rather than pivoting in one plane. I removed that bellcrank and the two pulleys on it and found the spacer that it pivots on was worn, as well as the hole in the bellcrank it fits into (both are held onto the tractor frame with a bolt).

So here's my theory: this bellcrank pivot point wore to the point where it was tilting downward at the front (toward the crank) and was both wearing the top edge of the belt (in previous times I found evidence of that) and/or popping off the top edge of that leading pulley and getting caught. When it got caught, the belt stopped and the crankshaft pulley wore through it. This reasonably explains all the symptoms I've been seeing.

For further reference, I found no evidence that the belt was riding deep enough into any v-pulley groove to bottom out; the parts book shows the same crankshaft pulley assembly for both engines.

Tomorrow I call a Simplicity parts dealer to see if the bellcrank, spacer, and pulleys are still available. If so, then ~$100 in parts (including a new belt) and I'm "back on the road."

I do have the Jonesin' for a new lawn tractor, but this ole gal has been so good for me it's hard to "quit her"...

Thanks, I'll keep you posted. - GA

There's always a reason if you look close enough or pay someone else to... but sometimes you pop a belt and all you did was pop a belt.

Are all your idler pulleys free spinning?

Yes, all pulleys turn freely.

I've ordered the idler pulley bracket and hardware to keep it aligned, we'll see if that fixes it.

GA

Hi all. I know this is an old thread but I wanted to update it with a Thank You to everyone as the instructions here helped me to figure out the same issue with my 8 yr old mower. It too shredded the original belt but I thought it was because of age. I put on a new a belt only to have it grind down and shred after about 30 mins of mowing on a perfectly level lot.

The mower is a Craftsman 30âÂÂ, single blade, mid-engine mower. I understand itâÂÂs actually a Murray that was very commonly rebranded MTD, Yardman and others, having come with the B&S 13.5 HP flathead engine. A double pulley on the crank has one belt to the blade and one back to a variator transmission. The second belt on the variator goes to the gearbox for the rear wheels.

After replacing the belt, the one that goes from crank to variator, I slowly pulled forward in the garage, stopped and looked under the frame. This is what I saw:

http://bellsouthpwp2.net/k/a/karlet/Mower/V1.jpg

http://bellsouthpwp2.net/k/a/karlet/Mower/V2.jpg

The hard plastic spacer on the bottom had slowly melted and that allowed for the parts to start wobbling around.

http://bellsouthpwp2.net/k/a/karlet/Mower/V3.jpg

http://bellsouthpwp2.net/k/a/karlet/Mower/V4.jpg

http://bellsouthpwp2.net/k/a/karlet/Mower/V5.jpg

http://bellsouthpwp2.net/k/a/karlet/Mower/V6.jpg

Interesting that the bottom side got hot enough to melt the spacer but the top did not. As you can see this thing is shot all to you know where. Replacement part is anywhere from $200 to $280 online when you can find them in stock. Heck I bought this from right from Sears for $500 dollars with the rear bagger. Someone had returned it after 60 days and Sears couldnâÂÂt sell it as new. They even gave me the rest of the yearâÂÂs warranty.

I really canâÂÂt complain. If I can grab the part for $200 and it last another 8 yrs. That works out to $2.08 a month. ïÂÂ

This post was edited by tamasic1 on Sat, Aug 31, 13 at 19:30

Thanks for reminding me about this one...as a follow up, the idler pulley bracket and hardware resolved my issue; the pulleys are now kept properly in-plane and I've not tossed a belt in over two years... - Greg