U20 Engine Problems

[Gregs672000]

I agree that is concerning. Looks like everything is sealing up, but a compression test doesn't always show issues... a leak down test would be a good idea. Bore scope too as mentioned. Something did cause the damage to the plug, and I agree that Phil's scenario as very likely. Hopefully you're OK, but best to take your time here.

[PandaBoy]

I had to back off the 19mm lock nut before running the valve adjuster all the way down to install the rocker arm so I assume that it was tightened up OK.
The metal bits (which are not magnetic) came out of the Air Cleaner Assembly when I tilted it over to remove it so I can't really say which side of the filter element they were on. I'll order a Bore scope from Amazon (no Autozone up here in Canada) & have a look.

[Gregs672000]

The metal looks like solder, which would be good as its kinda soft. Hopefully the combustion temperature would melt it quickly. It probably lasted long enough to hold up the valve, piston hit the valve causing the rocker etc to pop off, then proceeded further and snubbed the spark plug, and hopefully has exited and/or melted.
I've snubbed a spark plug before too, and it may have happened just as yours did with the popped off rocker (been long enough that I don't recall, but I know I never found the culprit or had problems afterwards). Roadster valves have thick stems and are pretty tough so they don't bend super easy. I've seen many pistons with clear valve contact and no bend in the valve, but I'm no machinist and have only my limited experience.

So far, so good. I think you're gonna be fine, and you may have dodged a bullet!

[redroadster]

The metal looks like solder, which would be good as its kinda soft. Hopefully the combustion temperature would melt it quickly. It probably lasted long enough to hold up the valve, piston hit the valve causing the rocker etc to pop off, then proceeded further and snubbed the spark plug, and hopefully has exited and/or melted.
I've snubbed a spark plug before too, and it may have happened just as yours did with the popped off rocker (been long enough that I don't recall, but I know I never found the culprit or had problems afterwards). Roadster valves have thick stems and are pretty tough so they don't bend super easy. I've seen many pistons with clear valve contact and no bend in the valve, but I'm no machinist and have only my limited experience.

So far, so good. I think you're gonna be fine, and you may have dodged a bullet!

It tweeks the valve head so it does not seat evenly not the stem
I've done many many Mitsu 4g63 s where the T belt stripped ...cust strapped for $$$ it tests ok starts runs but will begin leaking fire through the seat / valve
By the time they bring it back the machine shop say get a head somewhere.
Pop the rocker on ...what's the 1st compression pump psi that's the important reading if it's 30 and the others are 45-50 it's sure not something you want to rev high