Drain valve sizes for my Perkins 4108

[pcatterall]

Just overhauling some parts to eventually fit to my engine.
Several drain valves have stuck/corroded over the years and as a consequence annual draining has not occurred.
It would be nice to fit the correct drain valves.
Currently I am working on the Serck heat exchanger where I find that one drain has been replaced with a 'plastic threaded plug'
Seems to have worked ok and I guess the plastic threads will make a decent seal, however I would like to replace with the correct drain.
The od of the plug is 1/2" and I would appreciate advice as to the size and thread specification that I should be ordering for the Serck part and in general terms
for other drains on the engine.

 

[PlankWalker]

I put a gate valve and hose at the sump so it could be drained strait into a container.
Prety sure I used brass 1/2" BSP

Plank

 

[VicS]

Just overhauling some parts to eventually fit to my engine.
Several drain valves have stuck/corroded over the years and as a consequence annual draining has not occurred.
It would be nice to fit the correct drain valves.
Currently I am working on the Serck heat exchanger where I find that one drain has been replaced with a 'plastic threaded plug'
Seems to have worked ok and I guess the plastic threads will make a decent seal, however I would like to replace with the correct drain.
The od of the plug is 1/2" and I would appreciate advice as to the size and thread specification that I should be ordering for the Serck part and in general terms
for other drains on the engine.

1/4" BSP possibly.

You might be better off using plugs rather than drain valves, at least on the raw water circuit. They don't seize up or become blocked!