Scag belts keep breaking , Why ?

G

Greentoes

Member
My wife loves to mow, and when her father passed away, he left her his Scag mower (Model: STCII-61V-26FT-EFI).

She has been mowing since she was old enough to sit on her dad's knee, so I don't think this is an operator issue. However, we've had terrible luck with belts. We've replaced both the deck belt and the drive belt multiple times. We've used both genuine Scag belts and aftermarket belts, but we never seem to get through a full season without one or sometimes both breaking.

The mower has been serviced several times, but the dealer hasn't been able to determine why the belts keep failing. They're always happy to sell us another belt, though.

What should I be checking? Every time a belt breaks, it seems extremely hot. That could be because it just failed and was slapping around the pulleys, but it still seems hotter than I would expect.

My understanding is that this is a commercial mower, so I wouldn't think mowing for 2–3 hours at a time would be a problem. Our property takes about three hours to mow. My old lawn tractor would occasionally break a belt, but maybe only once every three years.

Has anyone run into this before or have any ideas on what could be causing the repeated belt failures? Any suggestions on things to inspect would be appreciated.
 
Are you referring to both deck belts?

Running extremely hot usually means the belt is too tight, there is a slippage issue, or you have an bearing issue. Now the PTO to Deck belt is suppose to be a 5/8 x 138 Kevlar belt and the short belt is 43/64 x 69 Kevlar cogged raw edge belt.

And sometimes a belt has to be change outside the OEM spec. Now on the long belt most of my suppliers are saying it is 138" but Stens is quoting 136". So you could be getting a 136" instead of getting a 138". OC belt I would try up it to 139" (B136K).
 
StarTech said:
Are you referring to both deck belts?

Running extremely hot usually means the belt is too tight, there is a slippage issue, or you have an bearing issue. Now the PTO to Deck belt is suppose to be a 5/8 x 138 Kevlar belt and the short belt is 43/64 x 69 Kevlar cogged raw edge belt.

And sometimes a belt has to be change outside the OEM spec. Now on the long belt most of my suppliers are saying it is 138" but Stens is quoting 136". So you could be getting a 136" instead of getting a 138". OC belt I would try up it to 139" (B136K).
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Thanks for your feedback I was getting the deck belt and I was thinking it was Width:5/8" Length:135 1/2" and the part number was 483243 if so then this belt is very short
 
I will replace it and then check all pulleys, look for any rough spots, and then run it and run it for 5 minutes, then check for any heat in any of the pulleys anything else i should check for ?
 
Greentoes said:
I will replace it and then check all pulleys, look for any rough spots, and then run it and run it for 5 minutes, then check for any heat in any of the pulleys anything else i should check for ?
Click to expand...
check your tensioner arms on the deck for play up and down. Bought a mower and guy said the main belt would jump off, had just enough play when mowing tall that the belt would jump off the main tensioner. There are 2 bearings stacked per arm and are cheap to replace - scag# 48224 Bearing# 99502H, mine is a STCii-52v, but should be the same part.
 
Random thought:

Is the breakage only occurring when your wife is operating the mower?
If so, is your wife pettit/light weight?
Could be that she is so light, that when she goes from forward to reverse or even corners sharply, her weight is comming of the seat/safety switch, causing the engine speed to drop rapidly, followed by her shifting her weight, engine rpm rises very fast to normal cut speed. The repeated off/on damages the belt.
Solution is to hang a weight off the back of the seat (do not disable the safety switch)
Dont ask me how I came up with this theory.
 
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Hello M.,

Glad to hear that took care of the problem.

Tension springs constantly oscillate thousands of times when the machine is in use. They get fatigued after years and hours of use.

Most people take for granted that a tension spring is still good because it has not broken yet. I have had new tension springs resolve many drive belt and deck belt issues over the years.

Install suggestion: Use an old section of pull starter rope or para cord to hook on one end to pull the spring tension and get them into place.
 
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