Low oil pressure kill switch

[Michael Oritt]

During the enduro at last week's SVRA Sebring event I lost oil pressure and though I shut down as soon as the light came on it was not quick enough to avoid burning up a couple of rod bearings and maybe worse. ( BTW this was in the sports racer which does not have an Accusump.)

During the long drive home I was thinking about plumbing a normally-closed oil pressure switch that would ground the coil in the event of oil pressure failure, with some kind of momentary switch to bypass it for starting, etc.

Taking the concept one step further I believe the pressure switch in the Accusump in my Courier has two circuits, one of which is normally open and is "made" by low OP which opens the valve to release the stored pressurized oil. I believe the other unused circuit is normally closed and perhaps it could be used to ground the coil and kill the engine at the same time as the Accusump valve opens.

I'm sure someone else must have had the same idea but has anyone done this?

 

[BuggerAll]

The Accusump does not open and close in response to oilpressure variations - it is always hooked in and supplies pressurized oil when the system pressure drops below the pressure maintained in the sump reservoir. I have a 20 psi swtich which is linked to a big red light on the dash (knock wood, the only time I've ever seen is is when I switch on, once I open the accusump valve before hitting the ignition it goes out and stays out). It sounds to me that if you ruined anengine right at the time the light came on, it was already in bad shape, it should have been resilient enough to handle a momentary loss of pressure. That said, I'm sure you could rig a bypass to the ignition which would short the coil when the pressure drops to the switch pressure. It would be a b*tch to have the engine cut out in a hard corner though, due to momentary oil starvation. Maybe it's time to examine your oil pan baffling - good luck!

 

[Michael Oritt]

The long story is that the two nuts that hold on the center main cap were in the pan when I dropped it so I guess we are not talking about a momentary loss of OP but rather a total failure.... The crank, pistons and rods are at M&O in Gaithersburg being evaluated--numbers 1 & 4 rod caps are black because obviously no oil got to them. The main journals and other bearing surfaces actually looked good but we'll see what Artie says.

I'm not clear on what you mean when you say that the Accusump does not open and close, etc. The pressure switch controls the electric valve which, as I understand it, opens to let out the pressurized oil if OP drops below the value of the switch. Can you clarify your statement?

BTW I have thrown my brilliant concept onto the large trash heap of other good ideas I have had--I agree that the consequences of suddenly losing power in a corner or whatever is way worse than damaging an engine.

 

[BuggerAll]

I have the manual valve on my accusump, so when it's open, it's open. I would assume that the Accusump with electric control works similarly, however. Perhaps this is a case of simpler = better. Don't know where your Accusump is mounted in the Elva, but if you can reach it, perhaps you should switch to the manual valve. Switching on and off just becomes a part of the start-up and shut-down routine. Perhaps other drivers with broader experience will weigh on on the manual v. electric issue - I hope your engine bits are salvagable. It's easy for me to pick up bottom end parts (MG Midget 1275). Has to be tougher with a Climax -

 

[PAUL161]

Check with Kohler, Briggs and gas & diesel welding machine builders, as they all have automatic low oil pressure shut down switches integrated in their engine systems now. Might be worth looking into. PJ

 

[Michael Oritt]

Buggerall--

I have a two-quart Accusump on the Courier with an automatic valve. The unit is tee'd into the return line from the oil cooler just before the oil filter with a check valve between the tee and the OC so that when the valve opens the oil will go into the engine and not back through the system.

The system is wired into the ignition switch and the automatic valve allows me to locate the tank remotely. I have it mounted vertically behind the right front wheel where it does the most good weight-wise and takes up no real space

I don't have a system on the IV--at least not yet.

 

[mike_h]

You've got me thinking now. I have an electric valve Accusump in my spit racer, I couldn't mount the tank close enough to the seat without a major cockpit redo.

Instead of killing ignition, wire the fuel pump through the low oil pressure switch, many road cars do this. You wouldn't get an abrupt cutoff but if you didn't notice the red light in time, the engine would gradually shut down. Since you may be in a condition where you need to run the fuel pump with low oil pressure, say pumping out the tank, a bypass switch should be included in the circuit. I believe my sump pressure switch has both Normally Open (NO) and Normally Closed (NC) contacts.

Besides turning on the tank valve at low pressure, I used the NC contacts to put small light at the tank. It lights up when the valve is on (low pressure), assuring me that it's working at a glance. If I run the fuel pump circuit through the NO (not conducting at low pressure)side. At pressure this switch should close (conduct electricity) and keep power to the fuel pump. When pressure drops low and it opens up, I'm running for a minute or so on the gas in the carbs and then it starts shutting down. A short drop in pressure due to a turn and the fuel in the carbs keeps me running.

Hmmmm

Will think this through some more but I see two downsides right now.

1.I wonder if the pressure settings for the sump switch might be higher (it might open at 50 Lbs now) than I would consider necessary for a kill the engine now condition. I might want to Tee off a second oil pressure switch that would trip at 20-30lbs or what ever I feel is a very bad sustained pressure.

2. Troubleshooting when it dies. If I don't notice the light, it burns out, whatever, this looks like a fuel system issue. The pump won't work, no power to it, I can see chasing this wrong path for some time until you come around to the oil pressure problem. Of course, if you have 20 PSI, good chance your weekend is over anyway but you never know, I've lost pressure due to the relief spring getting loose, 2 minute fix( 3 day debug).


mike

 

[Michael Oritt]

Mike--

I think this was a case of my simply having too much time on the way back from Sebring to overthink the problem and I am abandoning my genius concept, though I am definitely going to install a bigger and brighter low oil pressure light. <span style="font-style: italic">Maybe I should have 12VDC + and - leads with alligator clips that I could attach to a "sensitive" part of my body.
</span>
FWIW I don't believe shutting down the fuel pump would kill the engine quickly enough to accomplish anything and as you point out wiring stuff through the Accusump switch might point one down a lot of wrong alleys.

 

[John Turney]

Mike--

.... <span style="font-style: italic">Maybe I should have 12VDC + and - leads with alligator clips that I could attach to a "sensitive" part of my body.
</span>
....

I'm not sure 12VDC would be noticeable. You might need a few more volts.