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Low compression due to plug threads?

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Hello all,

Recently purchased a MS3 with low compression in cylinder 3.

Doing a compression test I find:

Dry: 150, 180, 20, 180

Wet(oil): 180, 180, 20, 180

Note 1: Pulling the plug from cyl #3 did not feel right, had to use ratchet the whole way up. Once plug was pulled out of socket, half of the ceramic crumbled into pieces. putting the plug back in was easier, but cannot put any tension on plug (Stripped threads).

Note 2: Previous owner mentioned Car was driven for 1 week with a missfire due to low compression

Speaking with locals, there was speculation that driving around with the misfire forced carbon build up on plug, and when I went to pull it, the carbon ruined the threads.

My questions:

- Could stripped plug threads cause a severe pressure drop like the one seen in this case?

- If not, likely the valves?

Thanks in advance!

I'd say that the stripped threads are a result, not a cause. If the plug is damaged and the ceramic is broken I'd say it is a result of severe detonation in that cylinder. It's possible for this to melt/deform the end of the spark plug which has in turn damaged the threads when the plug has been removed. I doubt this was related to driving with a misfire or carbon build up.