Hi Rusty, Ian,
I would be tempted to replace it. They are cheap enough
Regrettably, this is a can of worms for the uninitiated and the unwary:-
. "cheap" is the operative word; ime, equals-piss-poor-quality has been a problem for at least a couple of decades.
. Triumph and BSA only ever used used two o.p. switch threads:-
.. 1/8"NPT ((American) National Pipe Tapered) only on early '69 triples and twins;
.. 1/8"NPS (National Pipe Straight) from part-way through '69 onwards - i.e. far-and-away the vast majority of bikes.
. However, there were originally three o.p. switch part numbers - D1943 (the
one-and-only) 'T'apered-thread), D2133 (60-2133, including your bike) and 60-3719 ('74-on), so both the last two are/were originally 'Straight'-thread.
. Reasons why knowing the above is very important are:-
.. that couple of decades or so ago, some berk in the trade screwed-up royally - applied the D2133/60-2133 part number to the Tapered-thread switch; so, if you order using the part number in, say, a '72 T100 parts book, you'll be supplied a Tapered-thread switch instead of the originally-correct Straight-thread switch.
.. Ordinarily, that shouldn't be a problem as the maximum OD of both threads is the same (0.405"); the Tapered thread should
then taper downwards (@ 6 degrees iirc). Regrettably, given much of the trade's apparent complete inability to QC anything,
Tapered-thread switches that start around 0.4" OD but taper upwards
over the length of the thread have reached owners frequently.
.. Snag with particularly a twin's timing cover and an oversize Tapered thread switch owned by Big Spanner (in both senses of the word ...) is it takes very
little effort to crack the timing cover around the switch ...
If you must change the o.p. switch, the Golden Rule is:-
A Switch Should Fit All The Way Into A Timing Cover Or Crankcase Turned Just By Thumb 'N' Forefinger.
If It Doesn't, Remove It And Fix Why It Doesn't,
Never Force The Switch With A Spanner (Wrench).
However, even if a new switch does fit all the way into a timing cover or crankcase just with thumb 'n' forefinger, doesn't always mean it's the correct thread ... Every now-and-then, someone somewhere in the spares supply chain has a rush of blood to the head with the standard crap-quality switches and sources some from somewhere else. Unfortunately, they'll often source 1/8"BSP- or BSPT-thread switches - BSP is both one tpi different from NP (BSP 28 tpi vs. NP 27 tpi) and a smaller OD ... so the BSP switch thread'll fit in the NP-thread hole but, if the switch doesn't bugger the timing cover/crankcase thread when it's nipped-up, it'll piss oil when the engine's started because the threads don't seal on each other ...
Jeez ... you really couldn't make it up ...
After all, the moment you lose oil pressure the engine is not screwed:
Ime, this is not a wise belief or hope.
Actually reading Triumph workshop manuals will show various switch 'trigger' pressures, but no higher than 7 psi; otoh, "Normal running" varies between 60 psi (C-range) and 85 psi (triples).
From first-hand experience, I can regrettably assure any reader that a triple's bottom and top ends are well-and-truly donald lo-on-ng before the standard switch deigns to illuminate the idiot lamp ... The 1985 fix total still makes me wince today ...
Posted experience on BritBike and here (most recently by
?) suggests a twin's bottom end can
escape - possibly because of the oil in the sludge tube? - if
the rider's quick enough to switch off the engine; however, someone's still going to have to dismantle the engine to check ...
even with the oil light illuminated, if does not mean there is absolutely no oil flow
More experience or forum reading required. It can. A relatively-common occurrence on twins is inversion of Shonky-brand crankshaft/timing cover oil seals, meaning the input flow from the oil pump dumps straight into the bottom of the crankcase ... The recommendation is to check for and use only seals marked "Pioneer Weston" (sp?).
Given all the above, and the oil pressures even the Triumph workshop manuals say engines should
operate with, the switch and idiot lamp are ime and mho A
Idea - would any driver or rider with any real common sense be happy with a lamp that extinguished above, say, 10 mph instead of a speedometer?
My T160's and T100 have long had permanent o.p. gauges, the T150 is checked regularly with a bolt-on gauge.