Spark Plug Protrusion

[Honeymonster]

I have a re-worked cylinder head waiting to be installed as part of a top end overhaul and fitted an old spark plug to look at the protrusion into the head, the unthreaded portion of the body protrudes about 1mm into the combustion chamber, is this acceptable? I have looked at getting spacers but I can't find any on the market, should the end of the plug body be flush with the head surface, in which case, can I use a washer from another plug in addition to the original? Any thoughts?

[soulsurfer]

Yep, doubling up on the plug washers is a good idea if you're concerned.

[Honeymonster]

Soulsurfer,
Thanks for that, that's what I had been using on the old head, was wondering if I would get a suggestion for a solid washer of the type Champion used to produce but I can't find any so far, will just have to use ones from old plugs after opening them out a bit.

Seasons greetings

Ian

[Honeymonster]

Found some more information on this matter and the type of spark plug we use is termed a projecting shell type and the threads of the plug should reach the surface of the head with the plain end exposed in the head, hope this helps.

Ian

[oldbiker]

If the threaded part of the plug protrudes into the head. You may find that any carbon build up on the end of the plug damages the thread on the head as the plug is removed from the head.

A copper washer as others have surgested would not do any harm

[Honeymonster]

Quote 'with the plain end exposed in the head',
maybe I should have clarified that to 'with the plain unthreaded end exposed in the head'

Ian