Loose Spark Plug Insert

[dstates]

Well, it was one of those days... I had finished my first oil change on my 170A since I bought it. All was going well and I had started it up with the cowl off to do an initial leak check. I am SO thankful that my friend (who happens to be an A&P-IA) was there and he walked down the wing towards the cockpit and after briefly looking at the left side of the engine he told me to kill the motor. He saw one of the spark plugs moving. After shutting down we walked up to the center cylinder on the left side of the engine and could shake the bottom spark plug. As we investigated we found that the spark plug insert is loose in the cylinder. I’ve put in a link to a video showing how it moves and a couple pictures to show the parts in question. The spark plug is still tight in the insert. We looked from the top spark plug hole with a borescope and it looks the same as the video from the outside. I’m looking for anyone who has dealt with this before. My current plan is to call a couple places on Monday that do cylinder work to hear their recommendations. One is another local A&P and the other is Poplar Grove Airmotive.

Any suggestions or experience from my 170 friends?
Thanks!
Doug

[daedaluscan]

I am afraid that you need to replace that cylinder.

Think of it as a good day that you found the problem before it found you.

[hilltop170]

And check the rest of the spark plugs too!

[170C]

look on the bright side. At least you have those nice NON LEAKING push rod tubes!

Some of the more experienced members can comment on your problem, but maybe a new helicoil can be put in that spark plug opening.

[dstates]

I’m not sure if you are being sarcastic or not as I think the pushrods on the RH side are leaking...

[Bruce Fenstermacher]

I've had this happen on a A-65 cylinder.

Basically the spark plug insert is screwed into the head. On many, maybe all, it is held in place with a brass rod driven in a hole drilled into the plug insert and cylinder threads.

On mine we could unscrew the plug and insert as one. We had to heat the insert to get it off the plug. We cleaned up the threads on the insert and the cylinder. I do not recall how we screwed the insert back into the cylinder and tighten it, but we did. We then used a brazing rod as a new pin. The cylinder ran and was fine until I took the engine out of service.

What will have to be done to yours I can't say. But I won't say you will definitely have to replace rather than have the cylinder repaired.

[dstates]

Well, I ended up getting a new cylinder installed and had my first break in flight today. It ran great. Glad I did it. Here are some pictures from the process. A huge thanks to folks here and the great wealth of information from TIC170A!

#4 Cylinder removed

A look inside

Old cylinder

Old piston

Inside old cylinder

[dstates]

Inside new cylinder

New cylinder installed

[brian.olson]

Thanks for sharing progress, and I love "happy ending" stories like these. The photos you took throughout the progress are wonderful documentation. Congratulations to you, and I hope the burn-in process goes uneventfully and quickly!