Thrown blade belt

[cmac1719]

My church has a John Deere L 111A , serial # GXL111A086103 and it keeps throwing the blade belt. I replaced the belt 15 months ago. Rider has a manual engagement for the belt and with it off the belt seems very loose to me. Even when it is on, seems loose to me. They tell me it throws the belt when they are cutting the grass. Would a belt stretch much in 15 months? I don't see any way to adjust the tension on the belt.

 

[Hammermechanicman]

OEM belt?
All spindle and idler bearings checked?
Rough terrain bouncing deck?
All belt guides in place?
Has belt rolled over backwards?
Are they mowing at the lowest height setting?

 

[cmac1719]

Yes
Yes
No
Yes
No
Not the lowest, about middle

 

[StarTech]

Check moving idler arm for excessive play. Idler pulleys bearings should have little to no play. Also check the belt length 1/2" x 103.75"

 

[bertsmobile1]

Belts do not stretch , they wear thin on the V sides so sit deeper in the pulleys thus become loose.
Excessive wear happens because the belt is slipping on something that is not moving.
Good thing about belt failures is the actual appearance of the belt will indicate how & therefore why it has failed.

The usual culprit for manual decks chucking belts is wear in the tension arm pivot hole.
Yo will have to pull the deck out and move the arm by hand checking that it only rotates and does not move side to side and also there is very little flopping around of the pulley vertically.
If it jumps off strait away then take the spindle covers off get on the left side and have some one turn the blades on & off till the belt jumps off & try to see where it is happening.
At times I have been so desperate to solve a jumping belt I have clamped a Go-Pro under the mower to see what is happening.
With community mowers where the drivers might not be as familiar with the surfaces or as careful as they should be they tend to smack the deck into obstacles and long term this bends the front anchor plate on the mower back which of course causes the belt to go slack.

 

[StarTech]

Actually belts can stretch under load but usually return to the original length when not under load. Kevlar have a 1-2 percent stretch factor and poly belts have a 3-5 percent stretch factor which is the shock load. This explains why even a Kelvar will snap easier than a poly belt as a shock can easily exceed the stretch factor especially when the belt is a little too short for the application.

But said they don't normally stretch measurement purposes it is as said the V that wears thin. All it takes is one section to thinned (burned from slippage) to cause a belt problem. This thinning of the belt does have the effect of lengthening the v-belt as it rides lower in the v-pulley grooves.

 

[Hammermechanicman]

That and worn engine pulleys on manual engagement decks. I like the folks who don't take the time to loosen belt guides and just crank the belt over the sharp edge of the pulley between a rigid belt guide compromising the belt. My favorite is the mowers with the belt guide being metal ears bent down from the engine mount. You either remove the pulley or pull the engine to replace the belt. Seen some creative mechanicing on those. Or the guy that brings you a mower because it pops wheelies when you let the clutch out and he put a raw edge automotive belt on it.

 

[wrldtvlr]

I like the folks who don't take the time to loosen belt guides and just crank the belt over the sharp edge of the pulley between a rigid belt guide compromising the belt.

My walk behind has those. When I changed the blade I reaized I'd have to pull two pulleys to change the belt when that time comes.