a65 oil pressure

[TRIGWELL]

A friend has just fitted an Oil Pressure Gauge to his 1972 A65 Lightning - he has concerns that its reading 90 psi - and funny enough has developed an oil leak (surprise surprise) - what i have read is the oil pressure when warm, at 3000 - 4000 rpm should be around 40-45 psi - can someone explain this ridiculous reading for me? (the release valve has 70 psi stamped on it, its normally 50 i beleive)
ray t

[AWJDThumper]

With the engine warmed up, the oil pressure should be around 50 psi at 3000 rpm but when cold it will be a lot higher. Not sure without looking what pressure is stamped on a normal relief valve but it's possible the one fitted may have a higher rating than usual.

[JulianS]

From the parts books the OIF A65 was fitted with PRV part 71 2370 which is the same as fitted to the later OIF B25 after XE 2578 and was rated at 75 psi.

The 1970 A65 shown as part 71 1327 rated at 50 psi, the difference being the spring.

[AWJDThumper]

Looking into this issue a bit further, it appears, as Julian says, that the later BSA bikes were fitted with relief valves rated at 70 psi or so. However, my understanding is that the relief valve shouldn't be viewed as an oil pressure regulator as such but is better viewed as a blow off valve to prevent excessively high oil pressures being generated. If this is correct then the normal oil pressure measured is purely dictated by the pressure generated by the oil pump which is a function of rpm, temperature and viscosity of the oil. Around 50 psi should be normal at 3000 rpm.

In your friend's case, it would appear that the relief valve is not doing it's job properly as around 70 psi should be the maximum oil pressure measured. It might be worth taking it apart to make sure it is operating freely.

[JulianS]

Was the oil leak present before the fitting of the oil pressure gauge? Where is it plumbed into the system?

[JulianS]

PRV stamped 70 likely from a Rocket 3.