I experienced a new kind of glow plug failure today, breaking in a 1.50 two-stroke. In the middle of a static run, the engine just stopped. When I tried to restart it, I found I had close to zero compression. But no noises when I would turn the prop over, so I figured not an internal engine failure. The mystery was solved when I tried to put the glow igniter on the plug, and found a lot of wiggle in the plug. The electrode post was somehow blown loose, such that you could grab the post and rattle the body of the plug around it. Put in a new plug, engine ran fine, put it up and flew it the rest of the day.

Was it an Irvine 1.5?

Friend of mine had something similar happen many moons ago. I was holding the plane for him while he ran it up, and POP! The stem blew right out of the plug! Startled both of us, but it went straight up and didn't hit anybody. At first we thought it threw the rod or broke the crank or something (no compression)...
Sure is nice to just be able to put a new plug in 'er and fire it back up, with no harm done

Not an Irvine, it was an Aviastar--Chinese engine that Dave Gierke used to be distributor for, but now I see Sig has picked up this line. They are sort of a Chinese Moki. One of my flying buddies tells me this kind of failure is not common, but not unheard of either.

recently at the field I witnessed an engine toss the plug out entirely... apparently it was loose and just rattled out. funny part is that it was running great up until the POP, then it died and freewheeled some, leaving everyone on the ground thinking that something broke. When it came back the glow plug was just gone...