Rear tine diagram

I had this same problem and took the first advice about the shift fork arms being too spread apart. I took apart the gearbox apart and found that the shift fork arms did indeed spread apart overtime and with wear. I'm having a buddy weld some reinforcement to it as long as he can maintain clearance in certain areas as to not disrupt the operation. If it doesn't work then I did find the shift fork assembly part for $50, I just googled the part number, clicked on various sites, and found a better price!

Source: Yardman Rear Tine Tiller tines won't turn. Belt

Go here and you can download a free manual for your machine.

http://lawnandgarden.manualsonline.com/manuals/mfg/montgomery_ward/tmo39083a.html

Source: Replace belts on Montgomery Ward rear tine

I am not sure either, but I think that it would be alot cheeper to buy a new tiller, than to use your strenght fixing a old tiller that you didn't bother to keep the instructions for (no, I am not trying to be harsh. I am trying to be nice. and I am not sure about it coming with instructions, they usually do.)
Sorry, that is the closest picture that I can get.
Here is a link that may help. (IDK, because it is blocked where I am at.) http://www.google.com/aclk?sa=l&ai=CqcKEPGEMSvvXJJyotgeEiOyLB_jqoUWYtdrOBMib0rsYEAMoB1DU-N7X_P____8BYMmOo4qkpMQRoAGUt9H9A8gBAaoEIU_Q6ppHU85NtRLlGbCSz8M4YQ7k6yZkGAMPo_XJ9i4rSQ&num=3&sig=AGiWqtyvlB5FasgaU109ezFuPnc-65WzHg&q=http://www.fixya.com/support/roper%3Fcmpid%3DG3372595023

Source: Roper tiller 26 inch front tine Pulley/belt diagram

Go to sears.com. at top of page about center of page find parts. put in model #. It will give you a breakdown of the whole tiller.
R.G.S.

Source: i have a craftsman 17" 5.5 rear tine tiller chain

Check the Troybuilt website for specific info on your tiller.
www.troybuilt.com

Source: does rear tine tiller run 2 belts