Did you shear a roll pin in a drive shaft coupling? Cooling fan hitting something inside frame rail? Shear pin in the charge pump drive? Damage charge pump bearing installing a roll pin in the drive shaft?
I'd start with a sheared roll pin......might grab enough to drive trans on blocks, then slip (click) under load....pretty common failure...
Charlie, looks like that Original you posted has rear studs and lug nuts rather than lug bolts. Looks like it might have upgraded front hubs as well. The guard on the drive belt looks different than the brochure photo, different size and mounting setup.
Keith S. It's said that them that can, does, and them that can't, teaches. I think you're in too deep to give up now. Mike's idea about disconnecting the drive shaft is a good one - that will isolate the engine from the trans. Trans fluid is topped off? (Someday I'll tell you about the time I forgot to remove a paper towel that I'd used to get all the old fluid out before a fluid change). Keep with it, and keep us posted on what's happening - my bet is that it's something simple. Good luck!
The Kohler K301A that I had rebuilt a couple years back with the help from those here broke another connecting rod after only a few hours of operation. (This all happened back in Dec 2016-Mar 2017). I ended up purchasing a Kubota B-Series and my Cub 124 has been sitting behind the shed while I have been looking for a replacement engine.
I've been having trouble finding a K-301 that will fit my narrow frame cub for a reasonable price. That brings me to my question:
Is there a drop-in or near drop-in replacement engine that I can do a re-power with?
Sorry to hear about the rod failure. Did you install the rod with the correct orientation? The lubrication hole on the rod at the crankshaft end must be facing in the direction of the camshaft. Otherwise it won't have adequate oil for lubrication and will have a premature failure.
JASON - If there isn't a hole punched in the block of your current K301 you should be able to replace the conn rod. Last I knew a Kohler OEM rod was $100, a STENS was $40. You would need a seal and gasket package too.
A K241, 10 hp drops right into your 124. A K321 14 hp swaps in IF you swap the flywheel, blower housing, and backing plate. A K161/181 would fit also but If you plan on working your tractor you would miss your old horsepower. K341 16 hp engines used to be very expensive, the pullers drove the prices out of sight. Also dried up the supply of rebuildable engines.
You can find the OEM Kohler K-series service manual free on-line, explains in great detail how to rebuild your engine. It's all just nuts and bolts. Simple hand tools used. A set of feeler gauges, an inch-pound torque wrench are about all the "special tools" you will need. A piston ring installer and piston ring compressor and a valve spring compressor might be nice if your a tool junkie.
You don't say how you know the conn rod broke, but they should last 1000-2000 hours, one failing in an hour or two I suspect improper assembly.
I know this has been covered someplace... is the base of the block on a non-Cub K341 (in this case off an old Ford garden tractor) shaped differently to where a Cub K341 pan won't fit? Charley or someone posted pics at some point, but I'm suffering from Geezer memory today...