Unusual spark plug....

[macrae1979]

Usual story.....aquired an old 'gull from my father in law for my fishing boat after selling my Yamaha 8hp 2stroke as I needed the cash. The gull had been lying in his shed for about 4 - 5 years but he has used it many times before this for his boat on Loch Lomond so we know it works.

However I cannot get it to start up. I don't think it is getting a spark so I decided to change the spark plug, however, the spark plug that came out is one like I've never seen before. It says it is a Champion 8 com but does not appear to have any ground electrode or metal casing, it is just the white ceramic plug that has come out with the center electrode not being covered.

I know that the champion 8 com is no longer available, but the alternatives don't look like the one that has been removed nor do they look like they will fit as they are not wide enough.

I don't even know what model of engine we have as the engine number has been ground off at some point (dodgy).........

[Keith.P]

This probably daft to ask, but it sounds like you have only removed the center part of the spark-plug.
Most old plugs come apart into three parts, have you anything left in the plug hole?

[Vic]

This what an 8 COM plug looks like when new. It has an 18mm diameter thread I expect the plugs in your Yamaha were 14mm

[macrae1979]

Thats what I thought but what I think is the outer casing which is still on the engine body will not budge. I've tried everything, wd40, washing up liquid and other such stuff but still can't seem to get it to budge so I just assumed that was the way the spark plug was? I didn't want to force it too much incase I damaged the engine body casing.

I take it it WILL budge evntually?

This probably daft to ask, but it sounds like you have only removed the center part of the spark-plug.
Most old plugs come apart into three parts, have you anything left in the plug hole?

[Taspiper]

You don't have much choice but to remove it. Unfortunately steel plugs can seize very tightly in aluminium. You could try applying heat in the form of a gas flame but remove the tank out of the way first. Use a good fitting spanner so you don't round off the hex. Try hitting the spanner with a hammer in the undo direction, sometimes a sudden shock can release a thread that won't come under steady pressure.
Alternate heat and penetrating fluid a few times.
Last resort the head may have to come off for repair.(model dependant)
I had one so seized that the plug sheared in two. The resultant part had to be machined out and the thread repaired with an insert so all is not lost.

[macrae1979]

Well....wish me luck. Its not budging no matter what I use. Heating it up with a small flame it is then.......