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PK., Small Engine Technician
Category: Small Engine
Satisfied Customers: 1052
Experience:  Retired Owner of a full service shop and national parts sales website.
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My troy bilt bronco riding mower deck belt comes off the pulleys

Customer Question

My troy bilt bronco riding mower deck belt comes off the pulleys after I disengage the PTO. Is there an adjustment to tighten the belt when the PTO is OFF so it can stay on the pulleys?
Submitted: 4 years ago.
Category: Small Engine
Expert:  PK. replied 4 years ago.
Hi, what's the model number from under the seat?

The most likely causes are either a stretched/worn out belt or something interfering with the idler pulley which keeps tension on the belt. The idlers will have dirt and rust build up on them and often cause this. The fix is usually to remove the deck and give everthing a good cleaning and apply a little oil.

There should also be a belt guard on the engine pulley that prevents the belt from popping off. When you shut the PTO off, it's rather sudden and the deck pulleys will keep spinning which keeps the belt moving and makes it whip around. That guard should help keep it on the pulley. But if there's excess slack from a worn belt or the idler not keeping tension, it can still pop off.

But if you can give me the model number of your particular mower I can look it up and see which assembly you have and we should be able to get you mowing again.

Thanks, PK.
PK. and 3 other Small Engine Specialists are ready to help you
Customer: replied 4 years ago.
Model: 13AV60KG011 The belt guard is on the engine pulley but when the tension is less, it can pop off that pulley. It is a new belt.
Expert:  PK. replied 4 years ago.
I would go ahead and pull the deck off and pull the idler assemby off. If you've not done this before, take a few pictures of the idler assembly and the position of the springs. There probably isn't any drawing available that shows the position of those springs, so record yours.

Take a hose and a scrub brush and clean the deck and idler very well, let dry and put a little engine oil on the surfaces where the metals rub together. The springs should be very stiff, if not, then that could be your trouble, although they generally will break before stretching.

You could also have a bad pulley or even a bad spindle, but that should be somewhat noisy so hopefully it's just some dirt.

Let me know what you find and we can go from there. Thanks, PK.
Customer: replied 4 years ago.
Thanks for the advise. I replaced one of the spindles because it was worn. The other one looked and acted OK. Thanks for the tip about taking pics - hard to reassemble without drawings. Should I be able to move the idler pulley easily or should there be some strong tension on it?
Expert:  PK. replied 4 years ago.
It should move pretty easily however you probably won't be able to tell if it's moving far enough. Once you pull it off you should be able to see the wear marks and may be able to see if it has stopped moving as far as it should. You'll have a leverage advantage to moving it back and forth while attached, but the springs should be pretty strong when disconnected.

It is difficult to look at and see if there's a problem. It's really a try and see diagnostic, but it's also an annual maintenance item and something that should be done when you change a belt anyway.
Customer: replied 4 years ago.
Thanks. I'll give it a try and let you know how it turns out.
Expert:  PK. replied 4 years ago.
Thanks, just reply back on this thread. I'm usually online at night and will reply when I see your message.
Customer: replied 4 years ago.
An update: I pulled the deck and performed the maintenance you suggested. When I put the deck back on and attach the belt, in the PTO off position, there is about 5" of slack in the belt and I can manually remove it from the drive pulley (which is where I think it's falling off in the first place). It's almost like the belt is too big for this deck. I got this mower from my neighbor who was tired of dealing with belt issues (they were burning up and falling off). I ordered a new belt although I know this one is new enough. Should there be that much slack in the belt when idling? I would think not. I can take some pics and send them to you if I had an email address. Maybe I should call Troy Bilt directly and see if there is a smaller diameter belt that would work on this. I know the drive pulley constantly turns when the engine is running, right? or does it only turn when the PTO is on? I'm at wits end here.
Expert:  PK. replied 4 years ago.
Hi, that's way too much slack. If you're sure the belt is routed properly and the idler is putting tension on the belt, then maybe that's the wrong belt.

954-04045 is the proper part number. If your neighbor was not using that part, then maybe that's the trouble. Sometimes people will take the measurement and then try to match a belt up at an auto parts store. But if the width or the depth is wrong, they get an ill-fitting belt.

The engine pulley will always spin when the engine is running. The engagement for the belt comes from adding tension to the idler, which tightens the belt. Here's a link to the belt routing if you haven't already seen one:

You should have a paperclip icon on your reply box that you can use to post pictures. If you can't get that to work, you can send them to [email protected] and they can email them to me. I'll be offline until late tomorrow night but I'll reply when I see your reply.

Thanks, PK.