Colt Case Ingersoll Garden Tractors

Belts jumping off of mower decks can be caused by multiple reasons.

Incorrect belt, belt should be 9/16 width,
Pully wear
Mule drive wear
Mule drive mounting lugs on tractor
Spring tension on idler
Center spindle - deck bent and blade no longer parallel to deck



The mule mounting slots would have been parallel when new. Over time the slots hammer out and elongate.
Eventually the tractor mounting lugs may become obround.

When the belt is adjusted for a spring gap of 1/8" The deck will swing forward and hunt for a home position in the drive mounts. When the mounts slots and pins are loose the deck will change its hanging position during use. Even engaging the clutch will cause the deck to jump and throw the belt off. When the pins are worn like the ones in the picture the spring is all that is holding the deck in position. Even the slightest variation in deck to ground contact will cause the belt to throw off.

The first step in deck repair is to recondition the mule slots by weld filling and a grinding back to the original form. New lug pins can be installed on the tractor frame or welded and ground. New lugs can be made by cutting the head off of a bolt and replacing the lug.
When the lugs and slots are properly repaired the the snap fast locking pins will hold the mule in a stable position.

Some times the deck to mule mounting holes will need to be filled in and re-drilled.

As others have mentioned pulley wear can be an issue. Pulley wear and miss matched belt cross sections will result in high belt temperatures. Heat from slippage can shorten the life of a belt to a 1/2 hour. A poorly adjusted clutch will slip and cause the drive pulley to overheat and can shorten belt life.

Spike

Spike - thank you!

I can definitely attest to the 1/2 inch belts. Was using PO's well used belt up until last weekend when it jumped off. Right before it did I noticed it was running inside out (I knew it was done when installing this year but was waiting to see how long I could get out of it).

I replaced with correct 9/16 belt I had ordered previously (thanks Bill and Charlie at Barneveld!) and was back mowing in 5 minutes. What a world of difference. Way better contact with pulleys and the tension now can be adjusted correctly.

My newly acquired k45 deck has worn lug pins but everything is working well for now. This will be a good thread to come back to when I eventually get to reconditioning the deck.

Chad

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Great info Spike.

Here's an example of rusted pulleys on my old RM44 deck wearing out a 9/16" C23808 drive belt. Look at how far that belt is sunk into the pulley and if you look closely enough, the belt is no longer making contact with the sides pulley (look just below the part number and to the right, see the gap?). The internal drive belt had the same issue. In about a half hour the belt would wear down to the point where tension was lost and the outer two blades would slow down from the slipping belt (the front spindle drives the outer spindles).