I have sent a PM.

On my way back home from the Annual Rally, I lost, among other things, the chromed cover over the exhaust valve of my 1937 NH.

I have now two options: Draganfly have an unplated steel cover for £39.50; Single Spares have a cast alloy version for £32. The steel covers would be like the originals ...

I am sorry, but I also cannot think of any other cause for your problem. I haven't managed to avoid the build up of oil with the bigger pump and always blamed the higher oil drain hole in combination with the later, bigger pump.

Doesn't the 39 engine still have an oil pressure regulator? Then you can increase the pressure seen on the gauge by screwing in the adjuster of the regulator. Of course, Roger and Dave are right. A higher reading at the pressure gauge will not improve the oil circulation - rather on the contrary.

You can check whether the oil ways in the big end are clogged up by pumping oil into the hole for the quill. You need to pump for some time to see oil dripping out from the crankcase.

I use SAE40, which seems to be used also by many others. It made a significant difference on my engine. Have you checked which oil pump you have?

I read somewhere that the old oil thickeners were broken down much quicker than the modern ones, so that SAE 50 turned quickly into something thinner. The 1938 owner's guide for Germany actually recommends 30 for the winter to facilitate starting.

My quill is definitely somewhat off centre, but ...

With these timing cases there is always a lot of oil in the chain case. I also believe that oil can escape around the quill, especially when the oil is thick. When I pump oil by hand into the crank, there is a lot of resistance because the oil ways are really small. Excess oil then leaks out at the ...

Sounds familiar. Pre-38 timing cases have the oil drain holes much higher than later engines. This is my 37 inner timing cover:
IMG_20260331_135512.jpg
There are also correspondingly higher drain holes in the crankcase. Do you have the higher drain holes? Later covers have just one drain hole much ...

Yes, the unthreaded hole is the one I mean. I have a prewar bike where the hole is at a much higher level. Oil should come out from there. In the case with the cam you have a certain oil level, and that flows through this hole into the outer case until that oil level is reached in the outer case ...