MTFCA Forum

The spark plug adapters from 1/2" pipe thread to 14mm are available, but what it you have a head tapped for 14mm and want to use standard T 1/2" pipe thread plugs? I guess you're screwed. I'd like to add an explosion whistle, but I don't know of any adapters for 14mm plugs.

You could just drill and tap to the pipe threads. A 1/2 - 14 tap would require a 23/32 drill.

Or get a different head.

If I knew there was enough metal around the 14 mm plug holes without causing problems, I'd drill and tap.

A friend has a Z head with the 14mm plugs. He would like me to drill and tap for 1/2 plugs, but how much metal (aluminum) has been my concern as well. Chances are there is, but really don't want to mess it up.

I would expect that if the head was originally sold with either spark plug option, there would be more than enough material to support the larger plug variety. I highly doubt there would be a separate pattern just to accommodate the relatively minor dimensional change between the 14mm and the 1/2” NPT plugs