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Toro model 20200, serial number 315000XXX.

Mower ran for years without any mowing issues. Then one day, the belt that connects the motor drive shaft with the smaller pulley of the deck drive, shredded. See pic of that pulley.

Installed a new OEM belt and started the motor. The belt started chirping and then it began to turn the pulley and the unengaged blades started turning. In a minute, the belt burned up.

Installed a second OEM belt. Checked for slack in the cable...yes. checked that the spindle assemblies turned easily.... yes. Checked for deformed pulleys...no. Turned the blades and checked for plenty of slack in the belt....turning the blades does not make the belt turn, plenty of slack.

Started the mower with the blade disengaged and it started chirping again and the blades turned and burned up the belt again.

Installed a different belt, wondering if it's a manufacturer defect in the first two. Again, the belt started chirping and I cut the power to save the belt.

What could be wrong? The only thing that comes to mind is that the pulleys are at fault, but everything looks and feels fine.

Chirping means it is running against some thing that it should not
Usually this is because it is routed on the wrong side of a belt keeper or brake

It's talking to you and you are not paying attention.
Chirping is the belt friction.

You do know that the blades on your mower are timed and if your blade belt jumped during your repair process, which has happened to many of us, your chirping may be the blades hitting.

I double checked my mower to concur with your suggestions.

The motor sheeve has a guard but it's one that the belt easily slips under and goes around the sleeve.

The idler pulley pushes against the outside of the belt, activated by a cable. The belt itself goes loosely around both sheeves and the idler pulley doesn't touch the belt. The blades are perfectly timed.

When I started the motor, it would run perfectly for about a minute. Then one chirp, then another, and soon the blades would start to turn. So I said, engage the blades asap so that the belt would be working. But even that method after a short time would cause failure. The belt actually started on fire.

Otherwise, the bearings are all good. Everything spins freely.

"But even that method after a short time would cause failure. The belt actually started on fire.:

You either have a bearing locking up or the belt is rubbing something. "Chirp" tell me a bearing is locking up. Need a pic of a bad belt.

I was disgusted with it so I parked it in the shed for about 2 months. The belts are gone.

The belt in the pics is the final belt that chirped. You can see no wear on the side that touches the idler. The wear from about 45 seconds of running is on both inside edges. The belt is genuine Toro. The only bearing is the arbor and that is brand new.

so the first question is why did you replace the arbor? Was it for the same reason? Or was it something else? If so, what?

It appears that a v pulley the belt is running in is not rotating freely and the belt starts burning.
Probably a bearing seizure or the bearing is already seized and it's race is spinning in the housing and seizing after it rotates for little while.
Is this the primary belt from the engine to the deck or the secondary deck belt.

Either way it appears you need to remove the deck and inspect closely the pulley bearings. Several involved. Even the secondary belt pulley bearing can cause such but most likely the center driver area. It's not a safe thing to be trying to watch deck rotation as such with the pto in en-gauged even with the blades removed while off the machine or even having someone else watch.
With the deck off you can get a closer look/feel and most likely quickly locate the issue and re-build the deck at same time.

Is this your mower's part list???

This is a 30" walk behind. 20200

Initially I thought the arbor was bad because there was slight side to side shaft play. Thinking along the lines of sgkent, I thought it could be bad bearings. Changing the spindle assy didn't do anything.

As I was looking this over tonight, the engine pulley is good, the pulley over that spindle assy is good, the idler slightly touches the belt but it can't move any farther from the belt because the brake is tight against the pulley. If I rotate the blade in the normal rotation, the belt does catch on the pulley and the belt does move. The idler pulley cable does have slack when the brake is on.

There is lots of cable adjustment available if I would use a belt 1/2" longer, but that's not OEM.

There's several tips in your mower manual. Like this one below.

• Brush or blow out debris from the inside of the shield and around all the parts.
• Hold a 0.25 mm (0.010 inch) feeler gauge, a piece of paper, or a note card against the wall and slide it down behind the belt tension spring.
  Note: If there is a visible gap between the gauge and the spring, tighten the adjusting bolt and the nut until the paper barely slides freely in and out of the gap (Figure 36).

Another tip

• Important: Do not overtighten the adjusting bolt. This could damage the blade-drive belt.
• Install the blade-drive system cover that you previously removed.

Maybe the above was not directly related. Just mentioning OP might find a resolution in the mower manual again.

Most likely something is not aligned proper, someone might of hit a 350 Chevy engine block with the mower or normal wear and tear (bearings).

sgkent asked in post #8"
so the first question is why did you replace the arbor? Was it for the same reason?

Next question:
Did the belt issue start AFTER YOU replaced the arbor?
Did you change any of the pulleys when you changed the arbor?

Did you carefully measure your old belt's length OD and compare it to the replacement belts size. (I see it's only a 30 inch belt)
A hint also is the blade starts turning before even being en-gauged

Also here is a fittament note from flea bay about belt replacement on those models at this link. I suspect you could test a cheaper grade of belt 1/2 inch longer as a test. (instead of the higher cost Kevlar that is burning)

Exmark 121-5765-SL V Belt Commercial Walk Behind S X Series 30-Inch 121-5765 193308002408 | eBay

30 inches long

Fitment can vary by sub model, serial number, and/or production date of your equipment. Please refer to the original owners manual in order to verify this is correct part for your machine

Forest#2 said:

Please refer to the original owners manual in order to verify this is correct part for your machine

Click to expand...

Oh no no no guy. People don't use manuals any more. Just like road maps. Things of the past. LOL

Baymee said:

Started the mower with the blade disengaged and it started chirping again and the blades turned and burned up the belt again.

Click to expand...

So blades OFF, how did the belt get smoked? What did I miss?

Give it more slack at the cable adjuster.

Check to see if any part of your frame is cracked, I had a husquavarna 38 inch riding lawn tractor that was eating the belts, 3 different belts, found out the frame had cracked, had to replace the whole frame, from then on it was ok.

I know you have a 2015 mower and this bulletin is for a 2013, but it gives a very easy to follow procedure to follow when replacing pulleys and belts. Might just help you. http://fls.ixfr.com/144/136/Rotary Mowers 136 - REWORK-Spindle Nut and Washers FINAL.pdf

I will get back to this mower soon and check out your tips.

The engagement cable has no tension whatsoever. The brake block is fully against the drive pulley and the cable has slack.

Theoretically, the motor should run and the only contact with the belt would be with the motor pulley while the motor is running.

That's when it starts chirping after about a minute and the blades start turning, overcoming the brake block against the drive pulley

sounds like the belt is too tight or the wrong one. Or it is also possible the clutch isn't disengaging. Hence the belt is being told don't move, and you better move or else. It hemorrhages.To overcome the brake lock there would have to be lots of friction, right? At least that is my thought.

sgkent said:

sounds like the belt is too tight or the wrong one. Or it is also possible the clutch isn't disengaging. Hence the belt is being told don't move, and you better move or else. It hemorrhages.To overcome the brake lock there would have to be lots of friction, right? At least that is my thought.

Click to expand...

Yep, wrong size belt is sounding very plausible to me.

Post up a video of the belt and all related parts. Love to see you turn some idlers and other bearings too.

Something simple is getting missed.

Well, my neighbour up the street called me with the same problem. Same model mower. Here are his pics. The belt is very loose and not rubbing on the pulleys at rest

slomo said:

Post up a video of the belt and all related parts. Love to see you turn some idlers and other bearings too.

Something simple is getting missed.

Click to expand...

Something simple is getting missed.
Two mowers, same problem.
Neighbors has a OEM belt and it's going bad also.

Do a close inspection of the inside v-groove of both pulleys also.
That belt is going too deep into a pulley. I've seen pulleys get a hairline crack in the v groove where the belt runs and not readily apparently just glancing at the pulley. Had to look at both the outside and the inside with the pulley under a good light but usually could see that the v-groove had worn thin inside the pulley.

That's worth checking

Both mowers are the same vintage.

Yup pulleys are wear items guys.

Remember when it was new? Mower ran perfectly? What has changed.........

Well a lot of 2 items mainly. Dirt and wear from using.

Bearings are probably bone dry or rusted completely out. Lots of people use pressure washers, not a good idea.

If you have access to two similar vintage machines, remove some parts and look with reading glasses on. Close inspection will find all kinds of chaos.

I finally got the two pulleys, the engine and blade brake pulleys, and installed them.

This was for the second identical mower, with the same problem, not the original mower, for which this post originated.

Ran the mower for 40 minutes, with the blades unengaged, and not a peep. The blades never turned. Engaged and disengaged the blades several times during the 40 minutes and everything worked perfectly.

It required removing the motor, wasn't a fun job, but the $100 spent for parts was worth repairing a mower which currently costs $1500.

Thanks for the great observations! It was indeed a case of worn pulleys.

Good to hear you got it going.

I keep some anti-seize and a length of 1 inch wide sandpaper handy when I'm installing pulleys and steel rims onto lawn tractors shafts and similar stuff.

Not a fun job when encountering a rusted rim on a axle or a seized pulley on a engine crankshaft.