1987 115 Mercury Spark Plug Stuck In Head

HI, looking at purchasing a boat with a 1987 115 Merc in-line 6, boat & motor look fantastic for their age however the owner said when he did the last plug change there was one plug he could not remove so he left it in. Motor seems to still run fine since. Is this a common problem with this model or could it be a leaking water jacket around the plug that has seized it in there? Any help would be appreciated, i have loads of expierience with OMC's, Chrysler's & Suzuki outboards but none with Merc's

I'd leave it along until it has to come out, then be prepared to Helicoil the threads.

Jeff

No it's not a common problem. If it were me, I'd like all of my plugs to un-thread. I would try seeing if you could get it out yourself and perhaps you'll get lucky.
;

There is a product called "Freeze Off" that quickly chills the stuck part and adds a fine oil at the same time. Tilt the engine so the plug is pointing up. Heat the base of the plug with a propane torch for 30 to 45 seconds and then quickly spray Freeze Off around the plug base for 10 seconds to chill it. Immediately place a breaker bar and spark plug socket on the plug and give it a few taps on the end/side of the bar with a hammer CCW. What you are trying to do is break the seal. Repeat the heat/chill several times until it is loose. Use taps with the hammer so you don't break the plug.

i would not buy the motor until the problem is fixed...either the seller does it or gives you permission to do it..sooner or later that plug will have to come out...if it turns into a big deal you want it to happen now on his nickle..