I have a fully charged battery and replaced the starter relay a couple months ago. The starter will spin once then hang up. Sometimes twice then hang up. Do I just need a new starter? This is really annoying!

First thing I'd do is hand turn the engine and make sure it's OK. If so, you might try removing the starter and hooking jumper cables to it and see if it spins. By "hanging up," I take it you mean the starter locks up, and doesn't whine like it would if the bendix was bad.

It could be a bad gear on the starter, or on the flywheel.

Depending on the air temp the mower sits in-

Could be the weight of the engine oil also slowing
the spin-up of the starter where it just binds.

Also.... fully charged battery with a dead cell
will also give you this same grief. If you have a
charger w/ a JUMP SETTING try that.

The battery is brand new. It did it with the last battery as well. The engine doesn't have a rope start and it's very hard to move the flywheel by hand. When it sticks, I can turn the key and the relay clicks, but the starter doesn't move. I've hit the starter with a hammer, but it doesn't help much.

Lube up the shaft coming out of the srarter with grease. Take the plugs out so it is not working against the compression. Crank on it for a second or two at a time adding more grease as needed. Put the plugs back in and give it a try.

Disclaimer: Be careful because some gas may blow out of the plug holes.

Just went and looked again. There is a plastic piece and washer that has slipped down on the shaft of the starter? Never seen it there before.

Just tried hooking up the jumper cables straight to the starter. Still wouldn't turn. Lots of sparking, so I know it was getting good contact. Maybe it's time to bite the bullet. Where's the cheapest place to get mower parts for a Tecumseh?

Japan?

Check here

before you replace the starter, check the oil. if the needle in the carb didnt set, it will leak fuel into the crank case and not allow for the engine to crank. open the hood and crank the mower until it hangs up. keep the key engaged and put down pressure on the top of the motor and rotate it. sounds like its hanging up under copmression to me.

I had a starter do that once, like to have drove me nuts. Found a mechanic that told me that the bushings in the ends get worn just enough to allow the shaft to foul & make the starter lock up. My thought, replace the starter or find someone to replace the bushings.

I found a video that explains what the problem may be. It is an overhead valve engine. They say that the valves need to be adjusted as regular maintenance. They may not be letting off compression when they are supposed to causing there to be too much compression for the starter to turn the motor over. I ordered a new starter, but I will definitely try adjusting the valves. Nice to work on this while it's cool outside! Still need to take the plug out and try the starter just for my own mechanical edification.