I'm not a small engine/equipment mechanic, I just play one in real life!

For the past 2 years or so I've been finding some chunks of what appeared to be a belt.  Sure enough, upon inspection, the rear drive belt had chunks missing on it. Happy to say the front drive belt still appears in reasonable shape, as that one would have been quite a chore to change. It's not terribly surprising that it's the first belt to go on its way out as there's a tensioner pulley that puts additional stress on it.   It's amazingly things have held up for as long as they have as it's an MTD mower that's 20+ years old (and more then likely well over double it's  life expectancy, I imagine it's one of the few of this particular model that isn't in a scrap yard.)

First challenge: getting the old belt off:

The plan was to slip the belt off of the connecting set of pulleys that links the front and rear drive belts together via a gap between the top pulley (that the rear drive belt uses) of the set of pulleys and the body of the mower.  The problem was that the gap was too narrow.  I looked under the mower and studied the assembly,  I initially thought I would need to take apart the pulley assembly which would have been quite an ordeal.

There had to be a better way, and there was

There's gotta be a better way to do this.  I then saw the solution.  I noticed that the assembly was connected to the body by a bolt (the one with the large washer by the yellow spring in the photo below.)  If I loosened/removed it and pop it down a bit, I might be able to enlarge the gap enough to remove the old belt and get the new one on. Sure enough it worked. 

With a bit of a struggle, I got the old belt off and below is a side-by-side photo of the old and replacement belt:

Here's the view under the battery compartment with it around the other pulley (and in position with the tensioner pulley.)

What's that smell? (Murphy's Law strikes!)

At this point everything initially looked fine and I put the battery back in place.  My first clue should have been that the assembly was not freely turning when the mower was in neutral. I fired the mower up and drove around a bit. I then started to smell the burning of rubber after a bit.  I took the battery back out and inspected the belt.  The inner portion of the belt took substantial damage. I then saw the issue. Turns out there was a belt guard pin that it was rubbing against. Crap. Turns out it was hidden from view behind the bolt assembly that connects the pulley assembly to the body.  The good news at least is that it was easy to remove, put the belt in the correct position and re-attach. Below is a photo of the darn belt guard pin with the belt positioned correctly:

"We do it right, because we do it twice!"- Mustie1(Darren)

While the (now) damaged belt would still last for a bit, I ordered another belt, and hopefully get another 20 years out of it.  Now that I know about the belt guard pin, I can simply remove it before hand, which should make changing out the belt the second time go a bit easier.