Cylinder 4 plug issue when Serviced

[Dicky]

I do my own annual service and for the last few years I’ve noticed that cyl 4 plug always seems black on the nose and with electrode wear, all other plugs as fine.

Can anyone shed light on this ?

[Willsy1980]

Possibly a slight leak on the stem on 4 or a slight ring issue allowing a bit more oil burn on that one maybe ?

[Dicky]

You could be right because I’ve googled the problem and that was one of the possible causes. My only concern is that this has been noticed during several annual services and always No 4 cylinder. It would be strange if this was the only plug where my torque tench failed each time!

Thanks for you input though

[RobPhoboS]

Some photo's would help too 

[Dicky]

Next service due soon as the rain up here stops and I’ll post one

[Willsy1980]

On 08/05/2021 at 12:09, Dicky said:

You could be right because I’ve googled the problem and that was one of the possible causes. My only concern is that this has been noticed during several annual services and always No 4 cylinder. It would be strange if this was the only plug where my torque tench failed each time!

Thanks for you input though

Its not necessarily the torque on the plug, if oil is getting in from the piston rings causing a bad burn that would show as a cruddy electrode. In the same way it could be an injector issue on that cylinder. Swap it over and see if it follows on the next service.