SV650 piston hitting spark plug?

No doubt, hence the comment If that small piece stays in there, it would probably run a long time. Considering what had happened, it doesn't look all that bad aside from the missing pieces.

In the desert, I don't know if I would have taken it apart

 

You're right, there is a very good chance you could pull the plug and rev the crap out of it and spit the piston bits out of it and go on about your business for a while anyway...

 

Update - Finished project

It took awhile to get all the parts and I wasn't in a major hurry anyway. But I bought a pair of used pistons from eBay that were in good condition and replaced the blown piston with one of those. I also pulled the valves out and checked them (as well as their seats) over real carfully for any signs of damage. Everything seemed to be in good order so needed parts were mostly limited to gaskets, valve tappet shims and a couple of tools I ended up buying.

I started the reassembled engine for the first time around 10:30 or so this morning. I rode it for maybe 20 minutes during my lunch hour but didn't do anything crazy. I'm going to do an oil / filter change on it before riding it any more to get rid of any crap that might be lingering from having the engine open.

Suzuki wants $20 for a tool that holds the cam chain tensioner while you're installing it, but my Scottish thriftiness just wouldn't let me give in and buy that particular tool. Instead I spent about five minutes with a paper clip and some needle nose pliers. On about the third try this version of my redneck cam chain tensioner holder tool was successful, and I was able to use it to complete the assembly.



The bike seems to be running great now, so we'll see. Thanks again for all the help and input folks!

 

I still suspect you have a rod bearing going out. Possible that the piston hit the head in those spots and broke the top of the piston off (above the ring land). Detonation would leave some ugly burn marks on the piston crown, and that cylinder is NOT running lean.

Good luck to you, because I doubt you checked the rod for play up and down before reassembly??

 

If the bearing had spun (and then got pounded into a thin "shell) the piston would have been hitting the head consistantly and the complaint would have been a rapid tick or knocking, not squashed plug gap.
I saw no witness marks showing that the piston had ever touched the underside of the head, just missing ring land materal which is classic evidence of detonation.

 

Fo sho.

SV bearings dont just "lightly" spin and let you go about your marry way except for the occasional egg shaped power stroke that just tap the spark plug and nothing else. They also always leave evidence in the oil.

 

Obviously I didn't drop the engine, so I didn't split the case and use plastigage. But I did check the rod for up and down play by hand as that was a concern.

I don't think there is a rod or crank problem, but I'll be listening and watching for any symptoms of problems.

Changed the oil and filter and rode the bike (calmly) for about 110 miles this afternoon. So far so good.