John Deere 112 mower deck

tinny

Member
I have a late 60"s 112 and can not keep the belt that drives the blades on.
If I drive it with a socket on the blade spindle it stays on as soon as I mount the deck and power it it pops off.
Any ideas the idler pullys seem fine and the spindles seem tight.
 
Are you putting a twist in the belt from the motor to the deck and turning it backwards? Make sure the bushing in the belt tightener on the deck is loose and allowing the belt to stay tight. Sometimes those will get stuck in the tightener arm and not pivot the way it is designed.
 
No twist in belt. And the tightner moves freely(almost got my fingers). I used a drill on one of the spindles and ran both ways with out jumping off the pullys.
 
The belt itself could have a broken cord in it. That usually happens if they jump for any reason and it more than doubles the chance that it will jump again. If you take the belt off and hold it up by one finger, does it hang straight down, ir does it twist to one side? If it twists, that is an indication of a broken cord, or at least uneven tension of the cords within the belt.

You said that the spindles and idler were tight. Do they spin quietly with just a little drag or do they rumble when you spin them? If they make any kind of rumble or growl the bearings are dry. no grease in them. They may be heating up and the shaft loosening up and then it aids the belt in jumping.

The last thought is how rusty is the deck? I worked on an F725 that the shell itself was totally weak-nearly rusted through-around one of the idler mounts and the belt would jump off that idler too.
 
The deck has very little rust. I will have to listen to the spindles, idlers look and feel good no slop. Belt was new at 4 pm today and still jumped after I hit the pto to run it.
 
Is the the tensioner spring (on the idler pulley arm) the correct part (or has it been replaced by a weaker one)?
 
Found the problem the tension pully bracket was bent up just a tad. Bent it back and now can mow. All bearings and spindles were quiet and tight.
 

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