"one of the bolts that holds the bottom of crankcase to top had worked loose, almost falling out. Could this be the cause of the shaking or happen because of the shake?" Not just the one bolt. Perhaps all of them are loose then which would. IF you just put the engine on new last year, those have a 2 year warranty on them, that is the way to go. "find a better motor mine just blew up yesterday what a pile of crap less than 100 hours on it and bang!!" Phooey, typically this is caused by the operator neglect. Got a speck of dirt in gas, lodged under carb float needle causing gas to flood cylinder and contaminate oil. Didn't check oil level before using which would have found problem and contaminated oil caused rod to go. These are sturdy engines with valve adjustment being weak point. Needs done every year or two. Install and use fuel line shut off valve. Walt Conner

for most people its valve adjust but for a select few its the engine design itself. the piston gets lubed by the engine splashing oil. if you dont change the oil yearly and are not using the correct weight oil, the top side of the piston and occasionally the head also will create tollerances so tight even the compression release wont be enough for the starter to push thru. usually i sugesst pulling the engine apart and cleaning the piston, valves, rings, and valve head. get then super clean abd put it back together. keep up on the maintence and it should run fine. also check the seloniod, they do go bad and it takes all that CCA to get these engines spinning

Does the crack coincide with one of the head bolt holes? Do you know whether this engine has ever had the head off previously. I have never seen it happen in engines of this genre, but I have seen it in a large diesel engine wherein a cylinder head gasket was being replaced and the mechanic failed to "blow out" the head bolt holes with compressed air after removing the head, or before putting the head back on. The head bolt holes were partially filled with a mixture of coolant, diesel fuel, and engine lube oil. In addition to that, the tech had coated the threads of the head bolts with a grease type "torquing compound". To speed things up, the mechanic used a pneumatic impact wrench to "run the bolts in" prior to torquing them. The resultant extreme hydraulic pressure that was created ahead of the impact wrench driven head bolts caused the engine block to crack at 3 bolt holes. The cracks traveled from the edge of the bolt holes to the edge of the cylinder liner bore. It would be a long shot to try associating the crack in this Briggs engine to the circumstances of the big truck engine, but something as rare as this must be caused by equally rare circumstances.

my first guess is that you have compression problems ... - valves which might need adjustment. - valves which might be burnt. - valve seats which might be very loose and leaking. - wasted head gasket i assume you have electric start - I would probably start by simply trying to spin the motor by hand (with the plug still in the motor)... Trying to spin it by grabbing the fly wheel cover - or perhaps remove the shroud and then you can get a better grip on the fly wheel. If you can turn the motor over by hand (with the plug) without much effort or any kind of resistance (due to compression) you can safely assume you have a compression problem due to valves, head gasket, etc ... good luck