Morris Minor Owners Club

Threads in cast iron are usually coarser than unf, I notice from the link that 16tpi is mentioned, which is more like it. In fact i'd have thought it would have been a bsp thread.

I think the thread is 1/4" BSP parallel in the head and taper on the by-pass spigot.

The 5/8" UNF mentioned in the link was after they had drilled out the old tube and needed an oversize thread?

Someone on a Mini forum swears blind that it's 5/8" x 16tpi Whitworth Fine.

I believe it is UNS and not UNF. This was discussed before-see
http://www.mmoc.org.uk/viewtopic.php?f= ... NS#p455228
Regards
Declan

I have some hexagon headed blanking plugs which are 5/8" O.D. x 16 TPI (possibly Whitworth) and which I have used in the past for blanking off the bypass in the cylinder head. They may not be the correct thread form but they are near enough to be useable and I have never had any problem with them.
The blanking plugs sold and recommended as suitable for blanking off the bypass hose are 5/8" x 18 TPI. They are also suitable for replacing the large oil gallery plugs but you do need a 5/8" x 18 TPI tap and a 14.5mm drill.
The old short bypass hose stub (Part No: 2A242 short) has been superseded by (Part No: 12A2075 long) and will have to be trimmed to suit if required.

I agree with Phil.
Here's a photo of the stub showing the 18 tpi thread.[frame][/frame]