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[Haggis]

The oil would just run down and back to into the gearbox so the level would not rise.

[PeteF]

I think oil pressure warning lights have a use.
Lets say the light started coming on at tickover (but went out when revved)
That would give warning that something was amiss before catastrophe.

[Rattlebattle]

Yes, you’re right Haggis. The oil would leak into the inner timing cover.

[PeteF]

Yes RB and Haggis.
I think I've proved that's not happening with mine which was the object of the exercise and to give me something to do in the 'shop

[Cranky]

Dont forget to tighten the flywheel nut before replacing the casing. You did know it was loose did'nt you?

[PeteF]

Of course!

[Rushour]

There's a very good reason RE never put oil pressure gauges on the iron barrel Bullets - it would frighten the pants off the rider ! pressures can vary from 90 psi on a cold winters start to damn near zero on a hot summers day - yet providing they have flow they work fine...

[Rattlebattle]

Yes indeed. RE wasn't the only manufacturer to try to avoid frightening its customers. The pre-unit Triumph twins had a tell-tale button in the timing cover. The pressure dropped to virtually nothing when warm, so the little button used to go back in. It never seemed to do much harm though a lot of owners, me included, modified the timing cover to accept an oil seal. This was much better at maintaining pressure than a bush alone. On the unit twins Triumph dispensed with the tell-tale button altogether. The pre-war twins had a pressure gauge in the tank.

[PeteF]

I seem to remember a tell tale button on an early unit Triumph but to be fair it was a long time ago and all my Triumphs blur into one

[Wheaters]

Years ago I flew Puma helicopters. The main gearbox ran at a very low oil pressure when hot (I think it was 0.8 bar, about 11.5 psi) and on the pressure gauge the needle showed just under half scale deflection, so it sat almost horizontal. The gauge was probably purpose made for the aircraft, with an expanded scale.

Later MOD decided to fit a combined oil pressure and temperature gauge (before that there was just a warning caption for high oil temperature). The gauge chosen must have been an off the shelf item because the normal temperature reading was half scale but the oil pressure scale went up to something like 10 bars so at normal pressure the needle looked like it was hardly off the bottom stop. Feedback was given but the new gauges remained.

The MOD needed to borrow one of our aircraft for a trial; the test pilots weren't familiar with the type. The head test helicopter pilot obviously didn't look at the oil pressure gauge after start up. Then, as he was flying along he suddenly noticed the oil pressure needle sitting in its "normal" position. He thought he'd lost all the oil pressure (scary, tbh!) so he put out an emergency call and landed in a field! Caused some embarrassment when the RAF recovery team turned up because there was actually nothing wrong with it.