Strange Oil Pressure Light Behaviour - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 18 (permalink) Old 07-23-2019, 03:10 PM Thread Starter
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Strange Oil Pressure Light Behaviour

Iíd appreciate some views from more experienced owners on this. The oil pressure light has behaved this way since Iíve owned the bike some 2000 miles ago with no ill effects to date.

After a good run and with everything thoroughly warmed up I switch off the fuel when I get home and let the float bowls drain at idle. When the engine stops the oil light takes about 10 seconds to come on, this is with it having idled for a minute or so and itís pretty consistent. On two occasions when Iíve been out and just stopped the hot engine using the kill switch the light has taken several minutes to illuminate, twice Iíve removed the headlight to see if a connector has parted but it hadnít.

From a cold start it behaves more as I think it should, if I let the bike idle for a minute and then stop the engine the light takes about 4 seconds to come back on. I donít do this often but wanted to check the difference between a hot and cold engine. The results are completely the opposite to what Iíd expect and I'm sceptical about the indications when the engine's hot.
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post #2 of 18 (permalink) Old 07-23-2019, 03:31 PM
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A delay before the oil pressure light comes on after you stop the engine is normal on a Triumph twin, but it’s odd that it takes longer when hot. Maybe the sender switch is going funny.

If you have any worries about oil pressure, measure it with a gauge.
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post #3 of 18 (permalink) Old 07-23-2019, 05:28 PM
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Hi Rusty,

Most-likely ...

It Ain't Broke, Don't Fix It


Oil pressure switches 'make' the warning lamp circuit at some feeble piffling pressure; I've posted several times on several old-Britbikes internet forums over the years that it isn't really an "oil pressure warning lamp" - if you see the lamp on when the engine's running, it's an "engine fcuked lamp" and "imminent bank balance demise warning lamp" ...

Otoh, even tickover pressure should be 20 psi on a twin according to the Triumph workshop manuals; that your bike's switch goes many seconds after you turn off the engine (stop the oil pump) before pressure falls to where it can 'make' the warning lamp circuit says your engine is most-likely good; as @Tritn Thrashr posted,if you're that worried, connect a gauge ... however, I'd add, be prepared to be surprised by what a gauge actually shows you about your bike's oil pressure ...

Quote:
Originally Posted by Rusty1 View Post
After a good run and with everything thoroughly warmed up
When the engine stops the oil light takes about 10 seconds to come on,
when I’ve
just stopped the hot engine using the kill switch the light has taken several minutes to illuminate,

From a cold start
if I let the bike idle for a minute and then stop the engine the light takes about 4 seconds to come back on.
The Triumph workshop manuals for the twins state "Idling" oil pressure should be at least 20 psi while "Normal running" is 60 psi; Les Williams defined "Normal running" as above 3,500 rpm in his oil pressure gauge kits' fitting instructions. So, if the engine's cold and you stop it only a minute after you started it, the oil pressure's never reached "Normal running"; all you're seeing is the cold oil pressure leaking out after you stop the engine/oil pump, 'til the pressure falls to where the switch can 'make' the warning lamp circuit.

Hth.

Regards,

Stuart
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post #4 of 18 (permalink) Old 07-24-2019, 01:28 AM Thread Starter
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Thank you for the replies. I did have a theory that only once the crankshaft is fully warmed will the big end bearing clearances be optimal, that would take a good while to heat up.

I'll leave alone and stop thinking about it unless the pattern changes.
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post #5 of 18 (permalink) Old 08-18-2019, 06:41 PM
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Quote:
Originally Posted by Rusty1 View Post
I’d appreciate some views from more experienced owners on this. The oil pressure light has behaved this way since I’ve owned the bike some 2000 miles ago with no ill effects to date.

After a good run and with everything thoroughly warmed up I switch off the fuel when I get home and let the float bowls drain at idle. When the engine stops the oil light takes about 10 seconds to come on, this is with it having idled for a minute or so and it’s pretty consistent. On two occasions when I’ve been out and just stopped the hot engine using the kill switch the light has taken several minutes to illuminate, twice I’ve removed the headlight to see if a connector has parted but it hadn’t.

From a cold start it behaves more as I think it should, if I let the bike idle for a minute and then stop the engine the light takes about 4 seconds to come back on. I don’t do this often but wanted to check the difference between a hot and cold engine. The results are completely the opposite to what I’d expect and I'm sceptical about the indications when the engine's hot.
Hi Rusty,

Up to 10" is fine and normal. If I turn mine over with no HT using the kick starter and engine cold, the oil pressure light goes out immediately as the pump has pressurised the system, then about 10" later it comes back on, as the pressure in the system drops. If I do the same thing hot, the pressure drops faster, presumably because the oil is warmer and therefore thinner. Note; I have an uprated oil pump so the behaviour on our bikes may differ. However, what is odd in your scenarios are the occasions where the engine is hot but it takes several minutes for the light to illuminate. Surely the pressure has dropped well before that time and the light should have come back on? Of course I am assuming you were at idle when you hit the kill switch not at high revs with around 60psi in the system but even so, the pressure will drop off quite quickly, similarly to the other times you noted.

If I were in your shoes, I might suspect I have a sporadically sticky pressure switch. After all, these are generally just a spring operated contact and if there is a possibility that something causing the switch to stick OR it is just getting old and the spring is weak. I would be tempted to replace it. They are cheap enough and it is an easy job to do. I would want to be sure that if there was a real problem, that the oil light gave me some warning. After all, the moment you lose oil pressure the engine is not screwed: if you spot it early enough and shut the engine off you may be able to save an expensive repair bill. Additionally, most oil pressure switches are not "No Pressure" but are actually "Low Pressure warnings", so even with the oil light illuminated, if does not mean there is absolutely no oil flow (unless you have lost all your oil of course...). E.G. you can tickover for a few seconds with a failing pump without doing damage, however a few minutes running with a failing pressure switch not providing any warning is a different story.

Cheers,
Ian

Last edited by Boggie; 08-19-2019 at 04:56 AM. Reason: Correct auto correct
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post #6 of 18 (permalink) Old 08-19-2019, 05:40 AM
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Hi Rusty, Ian,

Quote:
Originally Posted by Boggie View Post
pressure switch.
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 ...

Quote:
Originally Posted by Boggie View Post
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 @Truckedup ?) 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 ...

Quote:
Originally Posted by Boggie View Post
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.

Hth.

Regards,

Stuart

Last edited by StuartMac; 08-19-2019 at 06:16 AM.
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post #7 of 18 (permalink) Old 08-19-2019, 02:43 PM
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Hi Rusty, have you tried removing the switch to see if it can be dismantled or simply cleaned out?

My money is on contaminants on the contacts or restricting internal movement. It might be that you can restore the original switch operation, ideally disassembling and cleaning it all properly. However, even if you cannot take it apart (and I suspect you cannot), a good soak in contact cleaner or flush out with MAF aerosol may well help. I guess in both cases you would have to push the ball in to get at the internals. It certainly would not hurt to try this.

Cheers,
Ian
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post #8 of 18 (permalink) Old 08-19-2019, 02:50 PM
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Just read on TriumphTalk that you can take the original oil pressure switches apart.
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post #9 of 18 (permalink) Old 08-19-2019, 03:27 PM Thread Starter
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Quote:
Originally Posted by Boggie View Post
Hi Rusty, have you tried removing the switch to see if it can be dismantled or simply cleaned out?

My money is on contaminants on the contacts or restricting internal movement. It might be that you can restore the original switch operation, ideally disassembling and cleaning it all properly. However, even if you cannot take it apart (and I suspect you cannot), a good soak in contact cleaner or flush out with MAF aerosol may well help. I guess in both cases you would have to push the ball in to get at the internals. It certainly would not hurt to try this.

Cheers,
Ian
Thank you Boggie. I haven't tried either swapping or cleaning out the existing switch mainly because apart from the two occasions when the 'lamp of doom' stayed off for some minutes the pattern appears consistent. When the engine is cold it behaves as I would expect, when it's hot the lamp stays off for much longer and it's been like this since I've owned it (2.5k ago miles now). While the con-rods are still inside the crankcase I'm going to leave well alone and keep an eye out for any change in behaviour.
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post #10 of 18 (permalink) Old 08-19-2019, 03:40 PM
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No problem. In case you ever need it, here is the thread. However, there is no feedback to say how the cleaning went....
https://www.triumphtalk.com/threads/...-switch.13411/

If you want to go new, assuming some of the posts above have not put you off trying.... About halfway down this page, you should find the correctly threaded new oil switch (at least that is what they say):
https://triumphbonneville.com/store/engi.html

Lastly: Don't be put off about scare stories about how much it costs to rebuild these engines: they are very simple and good quality replacement parts themselves are not expensive (you should see the parts alone cost I have for my 35 year old M635CSI engine rebuild). Of course if you get other people to build, rebuild and maintain your bike, it is a different story. Labour is not cheap but if you do it yourself, who charges for their hobby? It is all part of the fun....
🙂

Let us know how you get on. Good luck!
Ian

Last edited by Boggie; 08-19-2019 at 05:01 PM.
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