Replacing MTD Yard Bug drive belt
First: I hate to admit that I own one of these things. But, my wife wanted it, and she REALLY looks cute, in her short shorts, on it.
Second: The owners manual is darn little help. In a nutshell, it says "remove the old belt, and install a new one." (Okay, it says more than that, but doesn't really tell you how to do the job.)
Third: My repairman didn't want to work on it - he hinted that he would replace the belt for about a thousand dollars.
Fourth: You will need an impact wrench to remove the pulley from the engine. This is a good excuse to buy an air compressor and assorted tools for it. (Although the book says to use a 9/16" socket, you would have to grind the head of the bolt down from 5/8" to 9/16" for that to work; it's easier to use a 5/8" socket.)
Fifth: If you have determined that keeping the machine running is worthwhile, here's how to do it:
1. Lower the mowing deck all the way
2. Remove the belt guard from the top of the mower deck
3. Disengage the mower drive belt
4. Turn the machine on its side (the right-hand side)
5. Use an impact wrench with a 5/8" socket and remove the bolt from the dual pulley on the bottom engine shaft
6. Grasp the rear of the mower deck and swing it down and toward the front to get it out of the way so that you can remove the pulley
7. Pull the pulley assembly down
8. Find the square key that falls out on the ground - the one that locks the pulley to the shaft
9. Slide the new belt over the top of the axle, and place it on the upper of the two pulleys (the mower deck belt goes on the lower pulley).
10. Slide the pulley assembly onto the engine shaft
11. Align the pulley slot with the slot on the engine shaft, and install the square key (found in step 8)
12. Install the washer, lock washer, and bolt that you removed in step 5.
Now turn your attention to the variable-speed pulley assembly - the two-pulley assembly that is up against the back of the frame. It's held in place by a bolt that goes through the frame. You will note that intelligent engineering placed the pulley too close to the frame to be able to slide the belt around it, so you have to remove the pulley to get the belt on. The belt that you have just replaced goes onto the TOP pulley of the two. Now replace the pulley assembly and tighten it up. Route the new belt around the idler pulley, and you're done. Except, of course, for turning the mower upright (particularly important) and re-installing the deck belt and belt guard.
Now, to confuse the issue: The Yard Bug uses two (yes 2) identical belts to provide propulsion (MTD PN 754-0453, available off eBay from $25-40 each, or from Agri-Supply for $10 (A-S #63379).
Your owner's manual refers to the belt that I just told you how to change as the Upper Variable Speed Belt, although it is the drive belt nearest the bottom of the machine. It is on the upper part of the pulley that is attached to the engine shaft, and goes around the upper variable-speed pulley that is at the back of the machine. The other drive belt (Lower Variable Speed Belt, according to MTD) is above the transmission (just under the seat), and goes around the lower of the two pulley on the variable-speed pulley (back of the machine). So, the upper drive belt is closest to the ground, and the lower drive belt is farthest from the ground.
BUT, in MTD's defense, the upper drive belt DOES go around the upper pulley of the assembly that mounts to the engine shaft AND the upper pulley of the variable speed pulley (the one at the back of the machine). The lower drive belt, which is the top-most belt when the machine is upright, goes around the transmission pulley and the lower pulley of the variable speed pulley. GOT THAT?
If it's any constipation ... er, consolation ... the lower drive belt (the top-most one) can be installed by removing only the variable speed pulley at the back of the machine.
Now that I've figured all that out, and have new belts on that piece of (whatever), my only problem is that the engine won't start. I've got a headache. I have a strong urge to say nasty things about MTD engineering ... and quality. But I can overcome ... and so can you.