Why not look for a used motor on craigslist. I found hp ratings from 12 to 18 twin for $30-50. Bolt pattern is the same and an easy switch. Of coarse you can also pay a lot more.

Thanks for the response. It's definitely a Briggs engine. Or let me put it this way, there's a big 'ol Briggs and Stratton stamp on it. The model # is 31G77. I believe that's right. Good point. Getting a voltage reading is not a true indicator of whether or not the battery is good. It wasn't smoking, only when it conked out. It was laboring, laboring, laboring, then it conked out and threw out a puff of smoke. The reason why I'm GUESSING the engine is a little sieged is because when I turn the key, it appears I have good power going toward the cranking process (you can hear and feel that jolt of energy), yet the engine "stops" it. It's almost as though there's a heavy break on the engine. When I try and spin the engine from the top by hand, it won't budge. Then again, I have no idea if you normally can spin it by hand because I've never tried to do that! Sorry for being such a newbie. From the little research that I've seen taking the spark plug out and putting penetrating oil down it, waiting an hour then trying to manually move the pistons by hand as a *possible* solution. Again, this is assuming I'm right and the engine's seized.

This might turn out ugly. Begin by checking the valve lash or clearance as rcmoser suggests. There is a very specific procedure that you must follow when adjusting the valves on this engine. Speak up if you need to know the procedure. The 31 series B&S certainly has a valve train that will win no awards for longevity. At least not the awards you'd be proud of.

Does the free wheeling (bypass) valve operate smoothly in & out when you perform the purge, or if you are doing it to roll the tractor by hand? If the bypass valve does not move freely, and "click" into its proper detent positions.......it could be still bypassing a small volume of oil. As to "worn gears" being the source of noise AND ALSO being related to poor performance: Highly unlikely. The gears in this unit are the few that are required for just ONE reduction ratio between the drive motor and the differential section of the unit, and the differential gears themselves. The final reduction gearing would only be noisy during periods where the tractor ground speed was pretty fast and the pitch of the noise would change with any increase or decrease of ground speed. The differential gears themselves DO NOT have any relative motion to each other EXCEPT when executing corners (turning tractor to left or right) or when one wheel is spinning due to a loss of traction. At all other times the differential gears may as well be welded together as they remain stationary relative to each other. I suggest you might want to completely disassemble all the brake and friction pack parts for inspection, cleaning and lubing (where needed). Because Hydro Gear does list brake adjustment disorder as a possible cause of noise and poor performance, I am inclined to think that there may still be something about that friction pack and the brake caliper/pucks that may be at the root of the problem. If you put the trans into free wheel mode, are you able to roll the tractor at all by hand? If not....that may be confirmation of a dragging brake. If you undertake the disassembly of the brake and friction pack, be sure you take plenty of photos as you take it apart so you will know without question where each part came from and how it was oriented. Don't rely on the other manuals for that, they can sometimes be vague, but your own photos will be clear.