My guess is the hub is now damaged and the blade won't turn with the engine. You will have to inspect it. SOme of the old models had flimsy hubs to begin with. Possibly, you have sheared the flywheel key as well.

How hard is it to check the hub and the flywheel key? I'm pretty mechanically inclined and have done some reading. From what I've read it seems as though I might need some special tools to get into it. If I don't have to spend anything to figure out what's wrong with it I'd like to do that before I chuck it. And, if it is the hub or the flywheel how much money are we talking about to fix it? My husband doesn't like the mower anyway.

1) Well, you could try the hub 1st. The hub has to hold the blade securely to give the engine momentum to run. Remove the blade as you did before and pull the hub off. I don't know what style hub you have as I don't have the model #. In either case, there should be a key- whether stamped in the hub or seperate to hold the hub securely. Once that is secured you can remove the flywheel nut and may be able to tell if the key is sheared or not w/o removing the flywheel. As long the parts are limited to hubs and keys and such- the cash outlay is likely under $20.
or 2) trade it in if he dis-likes the mower!

Model # is 917.387300
So the hub is under the mower and has to come off first? Is the hub the crank shaft? How do you take it off? I've got the top pieces off to where the flywheel nut is exposed but it looks like the key is under the flywheel (according to the layout in the manual). I think you're saying the key is on the underside. Now I see something else in the manual under the heading 'Grass Catcher'. It shows the crank shaft keyway and something titled 'key' that is on the blade adaptor. When I look at that section on the mower itself I see the keyway and a slot under it which is lined up with the keyway. But they look like they are the same part. Maybe they don't look like seperate parts because they are dirty. So, are these the two things I'm supposed to be looking at to see if they are lined up?

When I spin the flywheel, oil pumps out of the hole which I guess is normal, and I hear a clunk. And now I see that it's just the blade clunking. Is the blade supposed to have a little wiggle in it? I can't seem to get it so that it doesn't wiggle. I'm guessing that's not the problem though.

Yes they need to line up with a "key" in the slot.

No, the blade should not have any wiggle in it. It should feel tight and secure.

Also, did you use the exact same sparkplug when you tuned it up? I'm wondering if the plug you have is too long (lets hope not)

Neal

I think I figured out the wiggly blade problem. I think the washer was put on backwards. Anyway, one side was really dirty/green so I figured it should point downward (my husband 'helped' take the blade off and put it back on so that's why there's confusion). Today, I flipped it around (it's curved) and not it's a tight as can be. I think it's on right now. I spent about 2 hours taking the blade, gas tank, housing and eventually the flywheel nut on and off. I was bound and determined to get the nut off and did so by putting a 2 by 4 under the mower and down the grass hole...technical name I know. Boy was I dissapointed not to see what I thought was going to be the key out of position. I saw a youtube demo and mine didn't look like their's. There wasn't anything there that I could tell. Tried to get the fly wheel off then, after yanking on it for awhile, I realised I probably had to take the blade off again. It seemed like I was so close but I'd had enough for one day and put it all back together. Tried to start it for grins. It didn't make the clunking noise but it didn't start either. Made sort of a gurgling noise and puff out smoke on a couple of tries.

So, now I'm still confused about the key. Like I said, the slot on the crank shaft lines up with a slot below but I still think it's one piece. The blade adapter fell off during the process and I slipped it back on down it's groove. I was kind of hoping that it might miraculously be fixed after that. So, now what do I do? I'll feel better about pitching anyway knowing I took a stab at it but I hate to give up before I know what's wrong with it.

I wonder about the engine being flooded from tipping. Look for signs of oil / fuel in the cylinder and air filter area of the carb. The key on these looks like an offset "T". See http://www.mfgsupply.com/m/c/23-8953.html?id=NeJvo79m for pic. Beyond that, you probably have exhausted your diy options.