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Well, this isn’t the usual type of tech tips, but I thought it might be interesting anyway.
In the summer of 1989, we had my old R Model, R103, that I drove in the 60’s, here for some work before I drove it at Watkins Glen NY. One of the things we did was to install an oil pressure switch that was used to shut off the fuel pumps with loss of oil pressure. It was basic. To get the pumps to run, it was necessary to crank the engine till it got oil pressure. Tough on the starter. When we got to Watkins Glenn, we installed the regular race engine that was being freshened up while the “R-Car” was in Evergreen. This was the first car that we had put this circuit on. We wondered if, after loss of oil pressure, the engines would be damaged while running out the fuel in the carb.
Well, we soon found out. The owner took the car out to see how it ran. While he was running down the back straight flat out, the engine shut down. The word came back that it had run out of gas. Actually, when it was towed back, it was found to have no oil pressure. Chip & friend George Potekhen started through the engine. The oil pump drive shaft had broken due to a piece of material that had lodged in the oil pump. Then they took a look at all the bearings. They were perfect. A new oil pump and shaft and the engine was running again. All I missed was one practice session.
The owner was ecstatic; having just spent a serous buck or two getting the engine freshened up. And we had a chance to evaluate our shut off system.
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We have installed the system on all our cars since then. But we have made the circuit a little more sophisticated. We found the three-pin oil pressure switch to be unreliable, so it was back to the basic single pin type that grounds to shell with no oil pressure. With the addition of a relay, this works to turn on the oil pressure light or run the pumps. To eliminate the need to crank the engine to get oil pressure & turn on the pumps, on street cars, we wire the circuit so that when the ignition switch is turned to the accessory position, the pumps will run and allow the carb to fill with fuel and the engine will start. Still, the pumps won’t run with the ignition switch in the on or start position until oil pressure is obtained. On the racecars, we have a center-off sp-dt momentary switch. In one direction, it turns on the pumps, in the other it runs the starter. Sounds complicated, but actually the circuit is very simple. It only requires some wire and about $25 worth of parts.
Following is the basic circuit:
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We can make up any custom circuits to suit your needs.
Sorry troops, it won’t protect the engine from an explosion do to structural failure.
Good Luck!
Walt Hane
Tech Tips-2
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