Aluminum heads

[Jeff M]

I have an old pair of Edmunds 8BA heads, but one of the spark plug holes on a head was drilled and tapped for a bigger sized plug. Is this a problem?

[HamerAuto]

put a heli coil in it

[Walt Dupont--Me.]

It's probably already drill to big for a 14MM helicoil. It's probably tapped for an 18MM plug. Accually I don't see why an 18MM plug won't work alright if you can get the right heat range. Walt

[paleot]

Have it welded up and drill it back to 14 mm

[36tbird]

I have the same situation on a set of heads I picked up. I haven't gotten around to actually search for a solution, but I heard that there are adapters that tractor guys use to put in new plugs.

[Pete]

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I would not weld it unless that became a last resort.
We generally fix that kind of thing with an aluminum plug threaded on the outside with an appropriate size thread, install it and drill and tap for the original size sparkplug.
Welding can bring on a lot more machine work like resurfacing, redomeing and flycutting over valves, not to mention loss of heat treat in the welded area.