I really like the looks of the -III OS engines, with the shiny aluminum case and the black iron fins.

So I impulse-bought a set of four OS 15-III "parts engines" off of eBay last week.  I think one is a runner (although it has the wrong prop drive) and at least two of the remaining ones can be made to run.

So -- what's the proper care and treatment of these?  I assume I want a high proportion of castor, and probably 20 or 25% oil.  What props do they like?  What size planes will they pull?

And -- anyone have a stash of prop drives sitting around?  There's only two prop drives for the four engines, and none of them are correct (one is steel, forced onto the crank of the "runner", the other is aluminum, too large, equipped with a funky cast-in counterweight, and badly chipped).  I may treat this as a chance to learn how to build and wield broaches, but that's crazy-talk when I should just be thinking of getting the engines running.

I sold mine back in 1961 when I had to give up flying to get a good pass in my matriculation exams—and I've regretted it ever since I returned to the sport almost 20 years ago.

I seem to recall that it could handle the profile Aeromodeller Peacemaker pretty well. That's a wing of ~285 sq in.

Other than missing out on the simple pleasure of filing a D-hole, you could just drill for a nice tight fit to the shaft and then thread the drive washer for a set screw. Grind the tip flat for more contact area to reduce Brinelling. It is only  a .15 so it should work fine. (The K und Beast 8011 .40 runs with a setscrew and a roll pin...thru the driver.) You might have to embed some tungsten weights (think Pinewood Derby) in the opposite side to reestablish the original counterweight effect in the cast part. Without machine tools that would produce the knurling, I would simply drill and embed some 1/16 music wire with 45 degree points ground into them. Think bumps on a McCoy drive washer. But I use wood props so that would seem workable.

That knocks the project down to something pretty quick. You could spend all that saved time and effort on building a B-24....

Dave

PS--I think these engines are supposed to be pretty powerful/high revving for their day. At least, I think I remember hearing that from a free-flight guy.

One other thought--

If the D-hole portion is only a 1/4" long or so, then I would probably try using one of the diamond scrollsaw blades that was recently reviewed here for use on carbon-composite parts. https://stunthanger.com/smf/building-techniques/scroll-saw-blade-for-carbon-composite/

I would rough out the part and drill the full size hole as deep as needed, then drill a smaller offset hole to feed the blade thru. A hardwood board (maybe some 5"x5"X3/4" maple) with a hole to use as a part holder (tack with a little CyA) and see how that little gem (sorry) does in aluminum. The blade would tend to self-guide on the full size counterbored hole--if you don't mind some scuffing there.

Anyway, lots of ways to try if you wanted.

McDivot