Over the years a great deal has been written about the oiling system of Triumph automobiles along with their characteristics and problems. I don’t plan to add to the mass of material but I do hope to put some of it into perspective. A Triumph engine with a good oil pump should have a maximum oil pressure of no more than 70 psi . At hot idle you should have no less than 10 psi and preferably 20. These are the basic guidelines. Oil pressure higher than 70 psi just wastes horsepower and adds unnecessary heat to the oil. It is a little hard to imagine what it takes to turn the oil pump drive rotor when you are producing 70 psi.
The original design of Triumph oil pumps (4-cylinder more than 6-cylinder) was marginal as to capacity to the point that, with old-style straight weight motor oil, once the oil warmed up and thinned out, the demand exceeded the pump’s capacity. This caused the pressure relief valve to close and cease having any regulating effect. However, with our modern multi-viscosity oils, notably 20/50 weight, the pressure relief valve retains its ability to function most of the time. That is why "clearancing" a pump to its maximum efficiency reduces the unnecessary thrashing the oil needs to take and the less heat is transmitted to it.
I usually try for .002 rotor to endplate clearance, and make sure that both inner and outer rotors have identical end float. The should, of course, be no noticeable side clearance in the lower inner rotor bearing. If the edges of the inner rotor tips look rough or scored they should be replaced.
With the new synthetic multi-vis oils on the market, the heat-induced thinning of the lubricant will be reduced further and the pump’s operating range can be extended. With a good filter, the correct lubricant and frequent changes, the pump can do the job it was intended to do and the pressures can be kept moderate.
A sudden drop in oil pressure that isn’t accompanied by bearing knocks can usually be traced to the relief valve being held open by debris in the oil... removing and cleaning the relief valve assembly will usually cure this condition. This valve is located in the oil filter head on the left side of the engine. On the upper surface of the filter head you will see the threaded adjuster, surrounded by two large nuts of different sizes with a lead washer between them. Loosening the larger of the two nuts will allow the entire assembly to be pulled out. Once removed, the smaller nut can be loosened while holding the larger one. It will now be possible to remove the adjuster screw, spring and check ball for cleaning. Be sure you count the number of exposed threads on the adjuster screw so it can be returned to its original position when you are done. While cleaning the various pieces, examine the check ball for any irregularites. It wouldn’t hurt to check the seat in the base of this assembly, either. Reassembly is straightforward. The oil pressure should now return, but might need a bit more adjustment with the relief valve screw.