2.5 petrol series 2a

can anyone tell me it the heater threads in the head of a 2.5 are the same as a 2 1/4 as I need to fit a heater tap into the head of a 2.5 petrol in my series 2a. thanks

the later heads on 2a and 3's moved over to metric which I am pretty sure it's M16 x 1 pitch which is a really fine thread, had to change the head on my engine because I had a crack in the head and replaced with a newer head, found out the temp sender doesn't fit you have to put in an adapter.
hope this helps.

may have to run a piece of copper household pipe with an inline shut off valve in it then thanks

Just looking at this issue for another reason, dedicated heater shutoffs seem to be quite expensive (£10-£30) but Toolstation do a 15mm ball valve for about £5 that fits 15mm copper and looks better made than the heater valves so I'm planning to try one of those in line..

that's what I intend to use