Bad news, good news

Bad news - just lost the electrode on the front cylinder plug.

Good news - Compression OK and no apparent internal damage.

So just retap of plug thread, major service, fork seals, head bearings, front caliper bleed screws and possibly, wp overhaul to do now..........................

..................except piece of spark plug embedded in piston crown.

why did it break off?

Slightly overdue major service, possibly. 63k on the clock but more like 6k plus since last service 'cos of failed speedo sensor.

Close to 70k in reality though if mileage with failed clocks added.

Will run as is and probably buy spare engine just in case.

Now that spark plug has a story to tell. Presumably whoever did it didn't believe in the notion that the first few threads should
be able to be turned by hand. I guess it's a consequence of it being a bast..d to get to. So ... you've got the head off and can
see the electrode embedded in the piston ... umm.

Electrode broke off and damaged the plug thread before embedding itself in the piston crown - thread damage to both plug and head was mostly done in removing the plug - head thread now retapped and good.

Your motor will more than likely run like shit if you do not replace the head and piston. There will be several divets from the electrode in them resulting in valleys and more importantly, peaks that will get hotter than the surrounding material (not to mention the embedded electrode) and cause pre-ignition. This is going to pound your motor (piston, rings, bearings) into submission in short order while providing substantially less horsepower and eventually stranding you out in the boonies somewhere.

Personally wouldn't do it but to each his own.

Good luck with it.

I guess there's only one way to find out................any more bets?

Head's not off (yet) so will run and see what happens - all delayed by major corrosion above fork seals so maybe the Kriega gaiters weren't such a good idea after all.

That's the spirit!
Me like.

Back up and running - no apparent consequences yet and only damage is financial from major service, new fork seals and head bearings, etc.

Clocks have just packed up as well.

1500 miles since and no apparent consequences......................new rear brake master cylinder, rear tyre, chain and sprockets required now.

Pretty amazing you are not experiencing major detonation...

Yep, still got all my bits crossed.

Engines are a funny thing, I'll say it will be a shelby (from australian shellberight) LOL
A mate of mine stalled and seized his honda cb650 in front of me with no oil in the sump. He didn't checked it for 22000km!
I rode to the next service station to get 3L of oil. We poored it in and by that time it freed itself and started up. All the doomday sayers said it was going to explode sooner than later. He did a total of 63000km on it after that, pretty much maintaining the same regime of service and it never failed.
Nr 47's bike it too mature to die now, it'll be fine!

It's good for at least another 50K!

Postscript to recent double engine rebuild - this was condition of piston as a result of broken plug electrode:

Comrade: That's amazing. I concur with Lowrance that it should have suffered from pre-ignition. Ouch! look at that chip out on the right hand side. What did the bore look like? Same?

Bore is fine and now back in use.