Spark Plug Thread Size

[SteveW]

Just a quick and hopefully easy question to answer:

What is the thread size for the spark plugs on a TC? The reason for asking is that I need to clean up the spark plug hole threads on my cylinder head and I need to know what size tap to buy.

[Steve Simmons]

If I'm not mistaken, it's 14mm x 1.25.

[frenchblatter]

Agreed,

There are only 3 sizes, 10mmm, mainly for race engines, 14mm for the vast majority and 18mm for tractors/industrial engines.

Or are there more that I've missed?

STEVE, I've got a tap, don't go buying one for a one time use. I can drop it down tomorrow if you want.

[SteveW]

Hi Norman,

Thanks for the offer, if you're passing by then please do drop it off. I can then give you back the last thing that I borrowed off you

I've got to be heading over to the observatory at about 4:30pm though.

Steve

[SteveW]

Thanks to Norman who went to the trouble of making a tap from an old spark plug when he found that he didn't have the correct size, the plugs now all fit as they should.

What I should have done was to check the depth of the holes before I bolted the cylinder head on. As near as we could measure in-situ, heads with a casting number of 22952 use short reach plugs, but perhaps someone could confirm.