My vote would be a 30 wt non detergent. The original was designed to use
the equivalent of 20wt, 30 wt or 40wt non detergent oil depending on the
ambient and operation temps. You don't say but I'd guess that the
Continental has either a full splash system or only a low pressure oil
system for the valves.

Detergent oils are designed to keep the crud in suspension (among other
things) , let it get back to the filter to get removed. Non detergent
oils will let the crud drop to the bottom of the crankcase as sludge.
I'm sure you have no high pressure lube and filter system, go with non
detergent.

Detergent oils did not exist in 1911. Owners manuals were close to non
existent. Quality specs on oil were non existent. You will have to deal
with the choice of going with a modern oil or the original.

If you did not have a chance to full desludge the engine when rebuilding
it, you could run a couple batches of lighter weight detergent oil to
clean things out. If you do that, only operate at fast idle, no heavy
loads or you take the chance of pounding the bearings out. Run until the
oil visbily changes color, replace.

..

Grumpy wrote:
Anybody have a recomendation for the creankcase oil to be usde in a 1911
Continental 4 cyclinder gasoline/ kerosene engine?