Just some things to consider:

I assume what was used was a two stroke injection oil (snowmobiles, scooters, outboard marine engines, and the old 3-cylinder Suzuki LJ off-road vehicle engines (I have an LJ20 from 1973) and not fuel mix oils (chainsaws, etc) which have few moving parts and are low demand, expendible engines.  

These 2T injection oils were developed for lubrication of engines that needed to be too small for a crankcase reservoir. Without circulation and re-use of oil from a reservoir these oils were designed to be total loss oils. The oils have a low viscosity, do their job, burn up (smoking exhaust is a charachteristic) and get constantly relaced with injected fresh oil. In comparison, old total loss oil motorcycles engines do recirculate the oil in the crankcase to some degree as evidenced by the buildup of soot and, over a prolonged period, settled sludge. 

To reduce smoking and to depend on a small reversoir of oil to inject, these injected two stroke engines are built with especially tight gap tolerances and must use a low liscosity oil accordingly. These oils, like Castrol 2T at cSt 40'c (the kinematic viscosity at 40 degrees C) are equivalent in viscosity to SAE20 crankcase oil. SAE20 oils range in cST 40' from 35-70.

I would expect these oils are as good lubricators as any engine oil and our old engines are likely not as demanding of the extreme lubrication performances needed by moden automobile engines.

Its the low viscosity of such oils trying to lubricate in engines with fat tolerances that I wonder about, engines designed with (assumably SAE50 viscosity oils in mind) as well as their unceryain capacity to be used over and over again as these oils would settle back into the crankcase, especially so due to their low viscosity. That is, they are thin, one-time-only consumption oils whereas the oils in old total loss engines actually are, to some extent, oil recirculatiion engines using oil having to lubricate over and over again until burned up or leaked out. 

At around 100 miles a quart consumption of oil, these total loss engines are burning up a lot of oil, but normally SAE 40-50 viscosity oils in fat space tolerances. Would a SAE 20 viscosity oil not burn up as much in these spaces (accounting perhaps for the observed lower carbon buildup), fall back to the crankcase more for reuse theyw ere not designed for?  

Did that answer your question? (haha) 

Bob

I brought this up on the AMCA website a couple years ago and Gene Harper mentioned that he used two-stroke oil in a 24 excelsior and he put 4,000 mi on it with no problems. He said the combustion Chambers were very clean when checking with a scope. We had also discussed using oil control rings but it was a little bit difficult to tune in the oil pump because you have to turn the feed down so far, he did say using oil control rings he had to stop and check his oil level at every stop at a gas station which is pretty much what you do anyway. I am setting up mine now to run this way so we'll see what will happen. 

Indeed, I'm the guilty party.  I've used 2 stroke oil in my 24 X with great results. It does have good oil control rings and NikaSil bore linings. I'ts not a problem to reduce the oil pump output down to a very low rate. Yes, after 75 miles, this water thin oil comes out thicker and black, like it came out of a 2 stroke Detroit diesel engine!  However, my 24 Chief looks the same when I drain it every gas stop, thick and black.  So clearly, the oil is breaking down because it's such a small amount doing a lot of work. It gets hot and dirty, so dump it often.  One nice thing too is, my engines run clean, meaning they don't leak oil all over the place, very little in fact.  I hate leaky, smoky  motors!  The 24 Chief will smoke a bit when riding in town, because the oil level slowly builds up and I'm using conventional oil.  However, get out on the road and it settles down and burns quite clean. The 2 stroke oil in the X is full synthetic and burns CLEAN, so even if it does burn a bit of oil, there is never any smoke from the tailpipe.

For reference, the 24 Chief with sidecar on the Cannonball used  about 1 1/4 quarts on the longest day, 325 miles. About half of that I dumped back in the waste oil bucket at the end of the day, leftovers from draining the crankcase at the gas stops.  The 24 X with full synthetic is very similar. I think the longest day we had was about 325 miles and it used less than 1 qt, again dumping at least half that much in the waste bucket at night.

In retrospect, I suspect the 24 X is actually using a bit more oil than it needs to. I think I could turn the pump down a but more and use less oil, maintaining the desired level all the while.  I suspect it is slightly over oiling and just burning that off, but it's smokeless so you never see smoke.  The X has a crankcase breather that is supposed to puke on the primary chain, but virtually no oil comes out of the breather, which contributed to the appetite for eating primary chains!

Here is a copy of the thread I posted on the AMCA forum a while back:   

It does seem absolutely counter-intuitive but I can say with certainty that using a good full synthetic 2 stroke oil straight in the crankcase of a total loss motor works fine, IF everything is right in the motor and you keep enough oil in the engine at all times.

I can confirm this personally after our ride last September. I've now put almost 4000 miles on my 24 Excelsior using the full synthetic Castrol 2 stroke oil in the crankcase. In addition, I add 1 oz/ gallon into the fuel. Keep in mind, we all dumped the crankcase oil and reset the level every 75 or so miles, when we gassed up. This amounted to 2-3 oz per stop, so not much really. There are two reasons for changing oil so often: First, it is for peace of mind. By changing the oil so often you can be sure the oiling system is set up correctly and nothing has changed. It is of course critical to have enough oil and catastrophic if you don't. Conversely, too much oil can be problematic as well, as in that case it starts blowing oil out every possible place as well as forcing it past the rings and burning it. past that, excess oil will cause the entire engine to immediately overheat and bog down, even stalling the motor. So, secondly to prevent excess oil buildup in the crankcase. The original engines did not have oil control rings, so they burned oil and the oil pump was adjusted to replace that amount as you rode. Installing oil control rings, which is a good thing, reduces oil consumption to a minimum. It can be difficult in some motors to get the oil pump turned down low enough to maintain the level, and not "make" oil in the case.

Our friend Hans Coertse from So. Africa rode with as and has also completed 3 cannonball rides, twice using this oil as well as many thousands of miles on other vintage runs in So. Africa over the years. Hans is the one who suggested I do this. He is the consummate engineer and looked at it this way: Regardless of how well the engine is built, even with good fitting pistons and oil control rings (or Nikasil cylinder linings like I ran) the total loss engine will burn some oil. Conventional oil burns and leaves carbon deposits, which can accumulate on valve stems, pistons, cylinder heads etc. These carbon deposits can build up quite thick and cause overheating or pre-detonation as well as break off and damage the inside of the motor. This is why owners manuals back in the day said to remove the cylinder (or cylinder head) and "de-carbon the pistons and combustion chamber every season". This is a pain in the butt for sure! So, Hans reasoned that why not use full synthetic oil that is designed to burn CLEAN, leaving only ash that will blow away? If that oil diluted 50/1 with gasoline will work in a 10,000 rpm 2 stroke motor why will it not work in these old, relatively slow turning motors? His experience has proven that it does, and the combustion chamber remains very clean and free of carbon n his bikes.

For me, I've ridden my 24 Big Chief sidecar rig for 30+ years on conventional oil. It does burn a bit of oil, especially if the oil level gets a bit too high, which can be tricky to regulate on any total loss motor. Over the years, I've put a good hard 15,000 miles on this rig, with sidecar and been into the top end 3 times, First time was after 25 years and it was caked with carbon, bores and pistons scored from carbon and exhaust valve stems caked as well. I tried the 2 stroke oil before the 2018 Cannonball but was afraid to do it, so I went back to conventional oil. In addition, the timing chest was a bit loose and the thin synthetic oil made it noisier. There are signs of carbon build up in the cylinders at this point, but not terrible yet, after 6500 miles since the last rebuild. The timing chest has been tightened up considerably and I will probably make the change to full synthetic oil in this bike as well. In comparison, the 24 X is whistle clean in the combustion chamber, as viewed using a scope. The engine still sounds as quiet as ever, so no signs of undue wear at this point.

So, I'm sold on using it in a total loss motor and will continue doing so. The only problem now is the tree huggers have put the squeeze on things and Castrol no longer sells this oil in the US. There are other full synthetic 2 stroke oils available though, just haven't tested them out yet.

Thanks Gene  for the detailed information which makes clear and decisive sense … I will be adding a dash of synthetic 2 stroke to my fuel mixture . I have been advised to do so by others but they have fallen short of the finer details that you have provided and eloquently portrayed. Cheers

I'm going to try that in my kx250 Harry,I got to find out