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Engine thread sizes, oil pressure switch.


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Trying to find what size is the thread in the engine block used for the oil pressure switch? 
I have been thru a Vitesse and Herald workshop manual but cant find any thread details. The Vitesse manual has a list of all the torque settings for everything on the engine, and this also lists the thread size, but it does not include the oil pressure switch. I found one reference to the switch (in the electrical section) that states its a 1/8" 27 TPI American Standard Taper. At the moment mine goes into an adapter so no sure if the block thread is a taper thread or not.

So does anyone know what size the thread is? And, more generally, is there anywhere a list of the threads sizes used on Triumph cars? I don't have a parts list so maybe it in that.



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I think that obscure electrical section reference translates as 1/8" NPT. The usual situation with pipe threads would be that the male thread (the switch) is tapered while the female (the block) isn't. All of mine have adapters in place (T-pieces for gauges) but all three are the same thread on all ports, and I'm fairly sure they're to that convention.

Edit: Apparently the taper-on-male-only convention is a BSP thing and doesn't apply to NPT, which would mean the thread in the block should be tapered. Hmm...

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BTW I am replacing the mechanical pressure gauge with an pressure transducer and need an adapter. I could buy one but as I have the time and the lathe and milling machine I thought I could make one :) I could take the old one  out and measure it...



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1 hour ago, NonMember said:

Apparently the taper-on-male-only convention is a BSP thing

Really?  I have taper taps for 1/8" and 1/4" BSP as well as parallel ones.......  I've only got a parallel die but that's just as it happens, taper ones exist.

Anyway, the oil pressure switch is definitely 1/8" and the switch itself has a taper male thread.  I'm not absolutely sure whether BSPT or NPT originally, but pretty sure BSPT (or even BSPP) screws in ok.  All the sideways facing gallery plugs on the 6 pot are the same but I think that on the 4 pot the others are 5/16" UNF and sealed with short bolts and copper washers.  On the 6 at least, the gallery end plugs are different again, and bizarrely, different either end.  


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