- Fri Feb 26, 2021 2:08 pm
#95454
When the oil is hot and running freely, there's no need for an oil pressure pump bypass (provided that the designer got his sums right).
The idea is to limit the maximum pressure to a level where the stress on the pump mechanism is controlled. The highest pressure is likely to be when the oil is cold and most viscous.
Most cars have some sort of bypass built into the pump assembly so I find it a bit surprising that on later "iron" Bullets this was deleted.
Three years ago I had a big problem with my Liege trials car, which I converted to use a three cylinder, Suzuki Swift 993 cc engine. The oil pressure relief valve in the pump assembly stuck closed one cold morning when I started the engine from cold. The oil pressure gauge reading suddenly jumped to read over the top limit (100psi). I initially thought that the gauge had failed because it had previously been reading erratically at times. However, it was obviously giving true readings and the high pressure reached was enough to distort the base of the spin on oil filter canister so that the sealing ring popped out of its groove! The engine oil pumped rapidly out into the engine bay and onto my nice block paving driveway while I left the engine idling while I shut the garage door. Thankfully, there was no damage done to the engine itself. The oil pressure relief valve on these pumps is very simple; there is a side branch off the main oil gallery and it contains a spring loaded piston sitting on a metal washer type seat. If the oil pressure gets high enough to push the piston against spring pressure, the excess oil is diverted straight back down into the sump. The piston in the duff pump on my engine was seized shut. I couldn't shift it even after applying heat and trying to tap it loose with a metal punch. A new pump assembly cured it.
Built like a gun... could go BANG!
