Cylinder Head Threaded gallery Plug

[Gizze]

Hi,
I'm in the process of rebuilding my cylinder head (1970 Elan Plus 2, with Webers) and foolishly tried to remove the first of the two threaded gallery plugs in between the exhaust ports on the side of the cylinder head to clean the internals.
I thought I'd be able to order some replacement plugs but every one that's arrived have been too small, and I'm now left with a part drilled out plug and no idea of what the thread size/ form is.
The thread is approximately 16mm dia, and the plugs the square holed type (similar to a sump plug) but a little difficult to tell the exact diameter on a part drilled out 40 year old casting - could anybody tell me the thread details please??
Many thanks
PS Once inside the gallery looked fine, no real cleaning needed !!!!!!!!!!!

[bcmc33]

The thread is approximately 16mm dia, and the plugs the square holed type (similar to a sump plug) but a little difficult to tell the exact diameter on a part drilled out 40 year old casting - could anybody tell me the thread details please??

The thread is most likely 5/8" UNC as its unlikely that a UNF thread would be specified for an aluminium casting.

[rgh0]

i have never measured these water jacket plugs up but I would guess 3/8 BSP which is very close to 5/8 UNC. If we dont get defintive answer I have a spare head I can pull a plug on and measure up properly

cheers
Rohan

[bcmc33]

i have never measured these water jacket plugs up but I would guess 3/8 BSP which is very close to 5/8 UNC. If we dont get definitive answer I have a spare head I can pull a plug on and measure up properly

cheers
Rohan

Rohan,

My first thought was 3/8 BSP - I measured it at 16.7mm diameter and 3/8 UNC at 15.9mm, so concluded that it was UNC.
I guess you're going to have to pull one just to give us the definitive answer.

[rgh0]

16.7 mm is almost certainly 3/8 BSP - is it a tapered hole thread?

[Gizze]

Fellas - many thanks.
If it turns out to be BSP this sounds ideal as a trip down the plumbing shop I guess will yield a plug!

[rgh0]

I just pulled a plug from a spare head I have here - defintiely 3/8 BSP by my measurents.

Appears to be a 3/8 bsp taper thread in the head and a 3/8 bsp taper plug . The plug is only 9.3 mm long so a bit hard to be definitive about the tapers especially on the plug

cheers
Rohan

[Gizze]

Down to the plumbers shop then - many thanks
G