Vintage Dirt Bike Q & A

I am restoring a 1980 cr250. The bike runs well but I noticed I lost a few ounces of transmission oil between changes. When I noticed this I completely drained the crankcase and measured the oil I put in then rode the bike for about 10 minutes. When I drained the oil again I noticed I lost 4 to 5 ounces. I know you will never get all the oil out that gets put in but I don't know what percent I should expect to come out. I replaced both crank oil seals when I rebuilt the engine and there was smooth action on the crank with no wiggle. About what percentage of oil should I expect to come out? I haven't noticed any oil coming out the exhaust and it doesn't seem to smoke more than a normal smoker of that age. There are no external leaks from the crankcase or around the drain bolt so if I am losing excess oil it must be going into the combustion chamber?

If I were trying to measure what is drained out I think I would let it drip out for an hour or so to make sure it was accurate. I can see it being a few ounces off due to the shape of the cases,low spots,ect.