912....blew the plug out of the head..!

Unfortunately, you have NO choice but to install a new cylinder head. There is no repair that will work properly and Rotax does not allow any type of Helicoil or other inserts, especially for spark plugs.

Hi All

According to Rotax the spark plug threads are not permitted to have helicoils installed.  Bill is right, it is the issue with thermo heat transfer that is the problem.  In addition you have very little room within the tiny combustion chamber.  I am sure that a suitable used head can be found, try someone like Lockwood Repair in Florida or LEAF in Wisconsin.  Both get scrap or timed out engines on occasion that are deemed non repairable but have lots of parts that are good.  

Some may question the logic of not allowing this work however we find that if any manufacturer has no guidance on how to accomplish the task (helicoil the spark plug) then it is not permitted for SLSA or certified aircraft.  If you fly an experimental amature built you can do whatever you want however there is no guidance from Rotax or any continued airworthiness procedures for inspection afterwards.  For the approved overhaul shops that work on Rotax it is expressly called out not to helicoil the plug hole.  ( that text is found in the overhaul manual) There are actually some parts that can be done, such as the magnetic chip detector hole however the guidance on how to do this is only found within the overhaul manual.  This suggests that only an authorized shop could do the work.  

Cheers

"at that point we really had no choice but to continue to use it as is (...for as long as it would hold I told him)"

When I read that statement, my blood ran cold...  Then I thought "I must have misread that sentence, let me  go back and read it again..."  But no, that's exactly what was stated...   Someone actually said they had no choice but to continue to operate a non-airworthy engine "for as long as it would hold"...  Even in the statement itself, there is an admission that they knew it would fail...

I'm sorry, but there was another choice:  Ground that engine until it was properly repaired!

The pilot's decision to continue to fly the engine in that condition was absolutely foolish - no other words to describe it.  That engine was obviously no longer airworthy at the point that the loose / stripped spark plug receptacle was identified. 

The mechanic absolutely should have warned the pilot not to fly that engine until it was properly repaired.  Instead, he seemed to agree with the pilot that "we really had no choice but to continue to use it as is."  Would the mechanic have told the pilot he had "no choice" but to continue to operate the engine if it had a visible hole in the cylinder head?  Or if one of the valves was bent so that it no longer sealed the combustion chamber?  This is effectively the same situation – a hole in the cylinder that is supposed to be sealed by the spark plug is no longer sealed...  

All parties involved were extremely fortunate that no one was killed and the aircraft wasn't damaged any more than what actually happened when the plug blew.  If it had happened at some critical point in flight, the results might not have been so fortunate.  Lawyers would have had a field day with the advice from the mechanic to "continue to use it as is," which I'm sure they would construe in court as malpractice.  

Thank God that no one was hurt, and the only damage was minor.  Extremely lucky!