Steinar Møll wrote:

I have a 1930 Indian 101 Scout, 45 ci. The motorcycle was bought new at Rjukan in Norway in 1930 and registered as a 2 seater. I don't have a motorcycle license myself, but I still enjoy starting it 1-2 times every summer and doing a little lap in the yard at home. I always check the oil level via the level screw on the engine before starting. Although the oil level here is correct, during the last drives it has thrown out a relatively large amount of oil, especially via the pipe marked in the attached picture. What could be the cause of this and is there any (hopefully) simple way to fix it? It didn't throw out that much oil before.

he crankcase oil level  is correct  my first sugestion  would be get a clear piece   of   plastic tubing   thats a tight fit on the breather tube    You marked      Long enough you  can blow and suck on    Blowing inwards  should  be  very restricted  and sucking should be easy    , This will  tell  you if the breather disk is  eithier stuck or missing  .  

I'm not much of an expert, but ...

For the owner:

The oil is blowing out the crankcase breather. Some oil normally blows out here when the crankcase is under pressure by descending pistons. Under the cover of the breather there should be a small, thin loose metal disc that covers the breather hole when sucked in when pistons rise and is pushed off the hole by air pressure when pistons descend (to relieve pressure - and oil normally goes out with it).  That's its purpose. Excess oil blowing out here is usually due to accumulating too much oil in the crankcase from either (1) sitting long periods and having oil leak through a worn oil pump - which is why you do a drain before you ride, or (2), excess oil passing through a worn oil pump WHILE riding even after you set the level with an initial drain. #2 has been happening with my 1931 101. The pump is too worn. ----- However, you also need to periodically clean out sludge that accumulates in the bottom of the crankcase. This 101 so infrequently ridden probably needs a good crankcase cleaning! This sludge with hardened particles can block the oil level drain hole giving you a false sense that you have drained excess oil when, in fact, you have not. The Old Skool method for doing this is to fill the crankcase with Kerosene (possibly that's "Lampe Oil" to you) and crank over the engine for a while without starting it. Then drain and refill to the proper level with oil. Repeat this drain circulation with oil again and drain again to remove residual kerosene followed with a final fill with oil to the proper level. Riding a bike often is good for it. Sitting not so good.

For the others:

I don't understand how a broken ring or stuck breather disk or other upper end cylinder problems can cause oil blow out (out the crankcase breather, but out the exhaust - yes) because the oil blowout out the crankcase breather must have a start with too much oil in the crankcase with that quantity of oil coming from the oil tank,  ring or cylinder wall issues cause oil and pressure to pass up into the combustion center and not immediately out the breather, and a stuck breather disk would not let this oil blow out.  

Bob

A very informative and easy to use tool to own is a compression leak down tester. No trying to kick up pressure for a cylinder compression test. This tool involves using compressed air thru a fitting in place of a spark plug and measures pressure loss over time in a special way, whether thru rings, valve guides, head gaskets, cracks in head or cylinder, etc. A comprehensive engine health check-up tool.  Due to limited clearance between heads and bottom of tanks, you will probably need to fabricate a brass 90 degree fitting to fit in there as these tools seem to expect you have overhead clearance above an automobile engine.