Tore down my PK with 20hp Kohler V-twin engine. I had to pull engine with shaft still bolted up to flywheel, as one bolt which is an allen head, was stripped over-size. Three came out real easy, this one never grabbed and now tool just spins, others didn't fit. So, now will be going out later and using pliers or vice-grips to remove probly. Is there a reason to use those allens there and not just good old hex head bolts? I know the allens are dark black, are they actually harder than say a grade 5 or 8 bolt? I'm thinking there is plent of room for the hex heads on that half of the joint mount, have to look for sure. These weren't very big diameter bolts, about 5/16", but kinda long. I used fraction size allens that fit tight, so not sure yet if should have been metric or is metric on threads. I was finding both type fasteners being used on tractor, mostly metric on engine and fraction on tractor. So, not sure what these are yet.
Not sure if just easier to build with allens on line or just why they would be used? They are fine, till they age and rust in like bolts do, and the tools damage them trying to get back out. They have pretty small heads too for size of shanks, wouldn't seem that would be better holding power? Most have washers at head, maybe that is torque spread?
I hate working on old things with allens, phillips head or even just plain slotted head bolts in the bigger bolt sizes, specially the tapered head kind. Very hard to remove when tearing things down.