Whelp! I found the problem.

It was December 30th, late in the evening, and I was on my way home from a friend’s house. It was cold. Third gear, maybe 55mph, nothing out of the ordinary, but then power started to drop. Concerned, I pulled over at the next convenient spot, maybe only a mile down the road. As the whoosh of riding wind subdued, and I could hear my engine more succinctly, I thought she might not be running on all cylinders. And then I heard the sound.
She died as I sought refuge in a lucky-to-find empty parking lot. Harrowed there, I called my friend. Perhaps if this situation did not improve they might be able to rescue me. But the bike started again, and so I continued on down the road. I did not make it far. With a clack, and a stutter, she made clear to me that something was wrong. And then I smelled it. 
The cold of that December night was no match for a well-outfitted motorcycle rider pushing a bike half a mile to the 7-Eleven. But that was as far as I made it. My friend came through. They were on their way with a trailer to get me and my bike home. 
The bike was making a sound, and had a smell. I could tell this was not something electrical. There was a “physical”-ness to it. There was a “burntness” to it. An “oil doesn’t smell like that”-ness to it. I wasted no time in getting the bike in my tiny shop and disassembling it. At first the suspicions were maybe a broken valve spring, or perhaps a broken piston ring. The head came off, and nothing was amiss. The cylinder jug came off, and at first all appeared ok, until I flipped it over. 
 

I removed the pistons. I removed the oil pan… and that’s where I found them. A bolt, a nut, both from cylinder #2’s con rod. A catastrophic failure of one 7mm-threaded bolt. 

And so now I am looking at a complete engine rebuild. I’ll post updates here a bit as I can.
I am admittedly bereft about this circumstance. I love this bike. I have vowed to fix it, but let’s hope I can. 

Stereordinary wrote:

And so now I am looking at a complete engine rebuild. I’ll post updates here a bit as I can.
I am admittedly bereft about this circumstance. I love this bike. I have vowed to fix it, but let’s hope I can. 

Looks horrendous but may not be so bad - did the piston contact the valves when it broke loose ? if not a replacement barrel and a conrod may be all you need. The bolt ain't broke so it looks like the nut came loose !!!!

I'd look for another engine. The crank and other things would be toast too. 

SWest wrote:

I'd look for another engine. The crank and other things would be toast too. 

I guess until it has been stripped, inspected and measured it's all "if's but's and maybe's" - it's that whole "crap shoot" of buying a 30 year old engine of unknown origin that has probably been thrashed within an inch of it's life ??

I guess until it has been stripped, inspected and measured it's all "if's but's and maybe's" - it's that whole "crap shoot" of buying a 30 year old engine of unknown origin that has probably been thrashed within an inch of it's life ??

Can't agree more, better the croc of shite you know than the unknown

Lets see what it looks like when it's open. Good to have spares I like spares. 

I have never seen this type of fastener failure in all my years of working on the smaller engines (650/750) Seen bent rods at the piston, but never any issues on the big end of a rod.

This is going to remind me to check the nut torque whenever I split one apart again.

I wonder if it would have broken the liner if it was not big bored? (I am assuming its a punched out 550)

Injected wrote:

I have never seen this type of fastener failure in all my years of working on the smaller engines (650/750) Seen bent rods at the piston, but never any issues on the big end of a rod.

This is going to remind me to check the nut torque whenever I split one apart again.

I wonder if it would have broken the liner if it was not big bored? (I am assuming its a punched out 550)

I wonder if the threads were dry or oiled ? I have a buddy who had this happen with a nearly new MV Augusta 750 but that one put the rod through the block

Wookie58 wrote:

…did the piston contact the valves when it broke loose? if not a replacement barrel and a conrod may be all you need. The bolt ain't broke so it looks like the nut came loose !!!!

As far as I can tell no, the piston never touched the valves. It looks like the entire cylinder head was unscathed thankfully. It will need at least one new con rod, but everything will need to be thoroughly inspected. 
(Side note: I think it’s funny that there are so many terms for the cylinder “barrel”, “jug”, “block.”)
And I believe you are correct about the nut coming loose. I’m surprised they don’t use thread locker on those. 

SWest wrote:

I'd look for another engine.

Already found one actually. Haven’t purchased it yet, but it’s good to know where I can get one, should that be needed. 

Injected wrote:

I wonder if it would have broken the liner if it was not big bored? (I am assuming its a punched out 550)

Actually no, it’s not punched out. To the best of my knowledge everything in this motor is completely stock, excluding only the cam chain tensioner, which I’ve swapped for the better late-model part.

Sort of surprised its not bored out as those liners look "thin" to me, maybe a optical illusion. A typical stock Kawi air cooled liner is about 3.25mm thick.