Not to hijack the thread but here is a K301 with a similar crack that I freshened up about late 1970s or early 1980s. At the time, I noticed a crack and stop drilled it, knowing how cracks tend to just keep migrating. The stop hole seemed to have stopped further extension of the crack. I would venture the engine has possibly a thousand hours on it since the time of refresh. It was just brought out of eight year storage, fresh oil and gas and she fired right off. BTW, the bore is still std and shows just slight wear. I am going to adjust the valves and re assemble.

Fatigue and fracture cause crack in metal bridge and even aviation aluminum structure, engineers come with this simple crack-stop holes solution but the hole size must be carefully chosen.

An air cooled engine is expose to greater temp variation so I'm a bit skeptical this solution work at long terms but it's your call and I wish you good luck with it.

As far the OP is concern his engine core is already good for the trash so no hole or even "magic" welding can save it from his grave, R.I.P

I had a conversation with the PO today. I wasn't mean about it, just showed him what was wrong including pics, and asked for an explanation.
The story, as it was told, changed to he didn't actually rebuild this one.. He had a machine shop he trusts do it, and has the dated receipts to show for it. Kinda irked me a little more, but whatever. I suggested he take the receipts and pics and information to the shop and stick a boot in somebody's a$$ and know for sure what he's selling before he makes it out to something it's not. Whether he does or doesn't make it right on that end, I'm still screwed...

On to better things. Talking with grandpa tonight (we live together), we know the 680 leaks oil, but otherwise runs great, the lift, body, PTO and brakes on the 680 have issues, and the 1450 is by far a superior tractor. So, we're going to work together, pull the K301 from the 680 , clean it up, fix it up, possibly rebuild it just for added assurance, and put it in the 1450 (should be a direct bolt in) till we can find a good K321 or better replacement.
The K321 sitting on the floor is froze up, and the K301 on the floor seems to be in good shape, but still the engine in the 680 sounds like the best option.
It's going to take some learning, and work I wasn't prepared to do, but seems to be our best option at the moment to get a good running tractor. Will update, or start a different thread, as we progress.

Well, as a glass half full kinda guy this is an opportunity to spend more quality time quality time strategizing a path forward with grandpa...

Update (almost 2 years later):
Lots of long story short- I got worse, grandpa died, couldn't do anything to cubs on my own, abandoned all gardening and mowing for a couple years (paid to get my 7 acres mowed).
Now- My condition is improving, I'm bound and determined to have a garden this year.
2 weeks ago, my brother came over and helped me go through with the original plan of stripping down the 680 and using it to make the 1450 into a working tractor. I should have taken pics of the process but didn't think about it.
Engine was about all that we used from the 680. Exhaust was shot, drive shaft bearing was shot (didn't know that till I saw it!) We did swap engine mounts because the 680's looked better. Almost switched mounting rails because the 680's looks to be better built and reinforced, but didn't want to get it all together and have to lift the engine again.
Air cleaner, exhaust and tins from 1450 reused.
My brother dropped the boat anchor (accidentally) breaking the governor and dipstick tube. Oh well.
I had an idea and switched the wiring so the PTO switch turns on the headlights and the headlight switch runs the PTO and rear lights (makes more sense to me!)
Installed engine, ran and tested for an hour, checked all bolts.
Installed grill, hood, side panels, more running around, everything went smooth.
Installed tiller, got it out in the pasture and had at it. Works great, even when bogged down! :-)

I did have trouble with steering and traction. Steering over plowed ground was next to impossible, and after the first pass with the tiller rear end was slipping in the dirt and taking me wherever it felt like. I never had those problems with the tiller on the 109. Ordered myself a set of Carlisle Tru Power 23x8.50-12's for my old winter tire rims. Already have the valve and liquid to fill them. Thinking about taking my front tires down to 3-4lbs pressure and see if that helps the steering until I can afford something better.

Got 2 good size garden plots tilled up and ready. I used to do 8, but 2 is all I want to try and tackle getting back into it.
For now, I'm just glad to be out and doing something with my cubs, even if it's on a (14)1250.
Got a little helper too! My 2 year old has fallen in love with "I'm driving tractors!" In the garden, I keep my hands on the controls, but when the PTO isn't running I sit back with my hands on my knees and let him take me around the property showing me all the boulders and trees, and he even drives through the trails in our woods without hitting anything. Got a future homesteader on my hands! :-)

Sorry for your lost, glad you get the cub back in services! You have your hands full with that little one, enjoy every minutes spend with him gardening, they grow so fast. :beerchug:

I've heard of guys using a roller chain to add a rib on the center of a tire to get better traction in snow; I wonder if that would work to help you in the garden if you've got any laying around. I need to do that, I can't steer mine in the garden with turf tires either.

Like this...

The kid AND the garden sometimes grow too fast!:biggrin2: Sorry, couldn't resist. Glad to see you posting and using your Cadet. Best of luck with the gardening this season.

Welcome back