Advice Needed - AME Mess Up or..?
 

Hello. Looking for some advice from folks with way more experience than me.

The other day I took my new to me 1977 Skymaster (and the first aircraft I actually own) in for an oil change and a few small snags. My well respected AME suggested changing the spark plugs because more than half were below tolerances. Sure! Next I get an email stating that while changing the plugs the heli coil backed out with the plug on #5 rear and can not be put back in as the cylinder is stripped. Now the cylinder must be replaced and I am grounded for over a week when there is lovely fall flying weather AND I had a business trip scheduled. Ouch!!!

Thoughts? Opinions??

If it was in for an oil change, why was he messing with the plugs?

Never heard of a helicoil but looked them up. Doesn't sound like anything your AME did wrong. The threads were stripped some time ago so a helicoil was put in. They may not have used enough eg. loctite to help stop it from backing out. Installation requires a special tool which is about $1200. If the helicoil backed out cleanly it may be re-installable with this tool. Is the AME implying that he does not have this tool? or that he is not comfortable for some reason doing so ? Is the cylinder is too wrecked to safely hold the helicoil?
Note that I am not an AME - was just curious about helicoils.

I had them look at a few things and plugs were determined to be below spec.

Most airplane engines have helicoils in ALL the cylinders from factory new. They normally do not back out when the spark plug is removed but it can happen.