Can anyone help in identifying the thread plug that should be fitted to the oilway terminations on a 54 B33 cylinder head?
I've removed a couple of bungs made from 5/16" BSW studding that only entered a couple of turns and wept oil. 5/16" BSC seems a marginally better fit, but even that locks up after a couple of turns.
Thanks
Petecylinder head oil way -02.jpg
I would say that originally it was BSCy and the fool who whanged in the Whit plug has damaged the thread.
A gentle restoration with a BSCy tap?
On second looks is it a Whit helicoil in there?
As you've probably found, they don't appear in the spares books. If it isn't BSW, then it must be cycle thread, but how many tpi? It may be 20 or 26; which one did you try?
V500 / Rog1 thank you for your replies.
It's not a helicoil and surprisingly the thread looks in good order. The best fit I found was a 5/16" x 26 tpi BSC bolt, but it only made a couple of turns before tightening up.
Could it be 1/16" BSPT? The diameter is about right and 28 tpi looks possible. I have ordered some brass 1/16" BSPT plugs on the basis that they could fit, but if not they shouldn't damage the thread.
Pete
BSPT sounds a bit obscure for BSA to use; tapered threads weren't usual on old British classics, but if it fits and does the job...
BSF is 5/16 - 18 . Screw a piece of round softwood in to count the threads.
Alan
Thanks Alan.
Excellent idea. Off to try it now.
Pete
Problem sorted.
The 1/16" BSPT plugs (7.72 mm dia x 28 tpi) have just been delivered and went straight in. It could be particular to my bike, there are a number of things that look as if they came from a plumbers merchant. Either way, all sorted, thank you to those who contributed.
Pete