engine oil viscosity and engine breathers

[volker.halbach]

This is about my 1937 open head NH. I am still having problems with oil coming out of the lower engine breather in the timing case. When I used SAE 30 running-in oil there was no problem. Problems started when I switched to SAE 50 with a few drops. Now it's becoming colder, and there is always a puddle of oil under the lower engine breather when I park it. It's not that surprising. The oil never becomes hot. Even after 50 miles it's just hand warm. The oil is never in the hot cylinder head, and oil circulation is minimal with the pump with the smaller delivery plunger. I also have the original timing case that has the holes for the oil back into the crankcase much higher than the later ones. I assume the hole is just too small, so the level rises and the thick oil is sloshed around in the outer timing case.

What do you use in pre-1938 engines? In the handbook they mention Castrol XXL for summer and winter, which is now SAE 40. But I doubt that the modern version has anything to do with the 1930s version.

The engine breather is the newer 90 degree elbow breather with a ball held in place by a split pin. I have the old 45 degree breather, but it doesn't have any ball in it. There is no hole for a pin, and I cannot see any provision for holding a ball in place. Were this old breathers just straight through?

[pete.collings]

Although this was with a much later model (VHA motor), I had modified the crankcases for the raised oil level in the camchest, and use to stop at a local shop on my way to work to buy a newspaper, The shop was 2 to 3 minutes from home, and there was always a leak of oil from the drive side breather as the bike stood. I used 50SAE oil, and I think when cold (especially in winter) oil clung to the flywheel sides (steel flywheels) and then passed into the breather as the bike was on the side stand. On arrival at work, no such problem when the motor had warmed up.

[paul.jameson]

On my 1937 Red Hunter I have, for many years, run with the 45 degree breather blanked off. The 90 degree one remains in place. I have the raised oil level in the timing case which I believe is there to lubricate the cam and followers better. Once the enclosed valve head came into use, extra oil from the rockers drained down the pushrod tubes onto the cam and followers which meant that the oil level in the timing case could be lowered.

[volker.halbach]

Thanks. I haven't blanked off the lower breather because it acts as an overflow in case the timing case is completely flooded and the oil would be pushed into the magneto otherwise.

I looked at owners' handbooks and they mention Castrol Grand Prix only from 1938 when the closed head was introduced. I suspect the open head engines need only SAE40 or lower even in summer. In the German version of the handbook they recommend oil that is thinner than Castrol XXL in winter, so probably SAE30.

[markus.nikot]

In the German version of the handbook they recommend oil that is thinner than Castrol XXL in winter, so probably SAE30.

Don't forget, we have colder winter in Germany than in Britain.

Markus

[JohnnyBeckett]

hi i the winter when it is very cold i use a Sae 30 and when it is not that cold i use a sae 40 XXL and i use GP 50 when it is very hot