I bought the 3-speed Honda Harmony II model HRT216KS3A in 2000 and enjoyed it the first year, although the cut seemed a bit uneven, the bag filled up fast, and the engine seemed to vibrate a lot more than it should.
I change the oil in early spring and again late in the season. I change the air filter once every 2 years.
Years 2-7 - the transmission has slipped more and more, now it'll only pull about 1/3 of it's own weight. It's a heavy mower so there's a lot of pushing for a lightly used (40 min runtime a week in growing season) $500 mower from Home Depot. And no - Home Depot carries no parts for the thing. From what I hear, I'm lucky to have my rear wheels still turn after 7 years.
I had a heavy, self-propelled Sears Craftsman that I used for 9 years before this, I used to cuss it - but overall, it was a better mower than this Honda, and was $300. Before that I had a hand-me-down Toro with an aluminum deck that was amazing - so light I could swing it in the air on turns.
Realizing I can't buy a quality mower for $110, I bought and installed a new tranmission for it. I had no idea what I was getting into when I began; I change oil on my cars and do light engine work, home projects, etc... so I'm no stranger to a wrench - but no master mechanic, either. Just don't try to tackle this without a good c-clip remover. I bought a cheap-o for $10 and broke it, then had to go get a good one for $20.
First of all, I drained the gas out to keep it from running everywhere - but forget about the oil. There were 2' puddles of oil all over my garage floor. I turned the mower upside down - the red plastic top was directly on the floor, a few scratches there now, oh well... Remove the air filter before turning it over because if you don't, it'll end up soaked in oil. Try to drain the oil before beginning.
There are 5 of these c-clips I had to remove to get the transmission & axle out. After you take the wheels off you can see a drive gear that's held on by a c-clip. Remove that, a washer comes off, then the gear, then a small moon-shaped bushing falls out - be careful, there's also a tiny spring inside a cut-out on the axle - remove that with needle nose pliers. It's this spring and bushing that is supposed to allow the mower to be pulled backward, BTW. Then two more washers come off.
I also removed two metal panels under the mower - this gives much better access to everything. In a nutshell, you want to remove the axle bracket on the right rear side of the mower (when upright, standing behind it) - this is on the end of the axle opposite the tranny box. By removing that, it allows you to slide the tranny and axle out the right hole, allowing you to remove the axle shaft from the left side.
There is a large spring under the tranny connected to the deck that makes tension on the belt. Once you get the axles pulled out the tension is relieved and you can turn the tranny over, unhook the spring, and remove the two drive cables hooked into it. There are set screws that allow this.
Reverse the process to rebuild it. I lost one of the flat washers that goes up against the axle gear, so I can't complete assy until I get the part. Be careful with the c-clips - if you bend them up, you can straighten them with pliers. Be sure to clean all the parts and use some good axle grease during assembly.
Take some pics along the way with a digital camera - if you get stuck during re-assembly, you can look at the pics to "see how it was" before you tore it apart!
If I had to do it again, I wouldn't - I'd pay the approx $90 labor to let someone else mess with it! Total time incluing a trip to the Hondaa parts house and two trips to the hardware store - five hours.