912 6 speed questions

Here is some reading on the 900 Series Allis Lawn Tractors.

To tell you the truth, I didn't see a belt tightener. It looked to me like the belt was tight all the time then turned when the clutch was engaged. I have taken some pictures that I hope might help. It's in the basement and dad took my light so I couldn't see very well but hopefully the pictures will be able to lead someone to help fix the problem. In the bottom picture, you can see that the belt is riding toward the outside of the pulley. The belts are being burnt off from the outside edge if that is another help.

Of the 3 pulleys in the top photo, the one farthest to the left is the tightener.  Look closely, there's a spring attached to the bottom of the bracket that that pulley is mounted on.  A lever near the left side of the rear hitch can be swung down to loosen that bracket and pulley.

Just looking at it, I think your belt may be too loose.  Besides slipping, the back side of the belt can interfere with the rear most pulley and get chewed up if it's too loose.  Flip the lever down to loosen the "left" pulley.  The bottom pulley in the top photo is in a slot and the bolt through the pulley can be loosened.  Then slide the bottom pulley 1/2" to 1" to the rear and re-tighten the bolt.  Then lift the lever up to tighten up the spring and tightener pulley.

Behind the bracket that the tightener pulley is mounted on (this bracket moves back and forth as you tighten the spring), there should be a colored decal.  The front part of the decal is red, the middle green, and the rear red.  The back edge of this movable bracket should be in the green------preferably in the front part of the green.

I can't tell for sure, but it looks like the tightener pulley is mounted in the correct tab on the tighten bracket.  It should be in the tab that points most directly to the center of the tractor.

Clear as mud, right!!


One thing else, turn off the mower before lifting it for transport.


Edited by 427435 - 29 Dec 2010 at 4:25pm

Got a J D  with same set up  Mower deck pulley got banged up against bottom of tractor and mashed pully to close. Look o k but belt would not stay on . Spred pulley out now its fine.

In your pic, that setup looks that same as whats on my 716H. I found when tearing down the machine to restore it, that the main pulley shaft had egg-shaped the frame rail out from wear. I don't think any kind of belt would've stayed on on that thing. Might be something to check out.....
Steve@B&B

One thing that was mentioned was to use the OEM belt. Another very important thing is that Simplicity designs thier systems to use thier own idlers also. You might find one simular but rarely will you find one to match the OEM style. If they are wobbling I'd recoment replacing bot idlers and the belt and try running it at low RPM's to see if the belt tracks true. If it doesn't then tweeking the angle of the bracket  may be needed to compensate for some wear or other unknown anomaly.

You may also need to "space out" the flat tensioner pully away from the spring loaded swinging bracket so that the belt, when running, tracks more to the center.  This can be done by adding flat washers on the mounting bolt between the center hub and the bracket.  This may help keep the edge of the belt from being worn by the flange of the pulley.

The idler pulleys can be rebuilt.  Drill out the rivets and buy a bearing at NAPA or Fleet Farm (it's a standard size).  Re-assembly using regular rivets or pop rivets (regular rivets preferred).

My son had a bad idler pulley and he found a replacement at the local Deere lawn and garden for around $12.  No Simplicity/A-C dealer nearby.

Using washers is also a good idea to get the belt off the edge of the pulley.


Edited by 427435 - 30 Dec 2010 at 10:09am