The spark plug installs all of the way and doesn't protrude too far,
that's not a problem. I'm concerned about detonation. It could be OK
initially, but in time the carbon builds up on the sharp edges and will
be like a glow plug, as Chuck pointed out. I guess I learned too many
times that if I know something's not right and don't fix it, it comes
back to bite me in the ass.
John
Charles & Peggy Robinson wrote:
> I would install the spark plug I intended to use and see if it
> extends all the way into the threads in the head. If it does I
> wouldn't worry about it. If it doesn't I'd be comparing the length of
> the threads in the new head to the length in the stock head. Ideally,
> the unthreaded plug tip should protrude slightly into the cumbustion
> chamner, IME.
>
> CR
>
> John Caffrey wrote:
>
>> Anyone have any complaints about the aluminum head manufactured by
>> Pierce? Overall I think it is a nice piece, but there is one thing in
>> particular I am not happy about. The spark plug hole was threaded all
>> the way into the chamber leaving several exposed threads, and sharp
>> edges where they break through the edge of the chamber. I bought a
>> fully assembled head and hoped to use it after checking the seating,
>> but now I want to machine away the exposed threads. Exposed threads
>> in a combustion chamber has always been a no-no, but usually we're
>> concerned with the steel threads of a protruding spark plug. Do all
>> of these heads come this way or is mine a reject? Are sharp edges of
>> aluminum not a potential detonation problem?
>> John
>> 67 MG Midget
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