RE: Ohlsson & Rice Antique Airplane Engine
Juggler,
First off, your engine is NOT a conversion. In the Conversions, The sideport intake pipe was removed or cut off and plugged. Because of the way the O&Rs are constructed, it would not be feasible for the home modeler to replace the crankcase so a new crankcase was not included in the conversion kit. Instead, one was instructed to either remove the pipe (If you had the proper tools), or cut the pipe then plug the hole. If I recall, a piece of soft lead was included as a plug.
That would mean your engine is a Factory front rotor. The fact that there is no cover over the timer assembly mounting area means that it was probably not a dedicated glow engine. Checking for a crankshaft flat is not always an indication of this as O&R used up crankshaft stocks until it was depleted. Another indication that your engine was most likely a gas engine and not glow, is the aftermarket Perfect brand needle valve assembly. The stock gasoline needle does not have enough taper to allow adequate flow for Alcohol (glow) fuels. By the time you've backed the stock needle valve out enough to get the engine to run without being too lean, it probably would have fallen out so, the Perfect needle valve was a popular addition.
.60 size O&Rs used a 3/8" THREAD size, NOT bolt size. The .60 size Champion plug is a V-1, when everything went to glow, Champion made a VG-1. Your plug is a VG-2 which is a glow version of the V-2, 1/4-32 spark plug used in the smaller displacement engines. As you said there is no adapter in your head then your engine is a smaller displacement engine. Check for any indication of an anodized color to the head. If there isn't, then your engine is a 19,23, or 29. The rare 33s only came in purple I believe. If the head was blue anodized then it would be a 29. Keep in mind that by this time O&R was fighting desperately for market share as there were more powerful engines available. As such there were very few 19s made as there was almost no demand for it. The 23 was always a popular displacement for O&Rs and 29s made more power so those two were the most popular.
The gas fuel mix for O&R was the typical 3:1 gas to oil but I've had alot of people tell me that 2:1 was better for them??? But, gas runs hotter than glow so I always run 3:1 when running glow fuel in my Ohlssons. I think if you stick to 25-33% castor oil you'll be fine. I've been told that they will withstand up to 5% nitro but I never did it. In fact, the final death of the Ohlssons was the problem of the .29s and .33s popping the cylinders off the crankcases when glow became popular and people started pushing them to try to keep up with the other engines available.
Also, the other problem is the gasket between the steel cylinder fins and the aluminum crankcase junction. It is prone to leaking. especially after the engines sit unused for a long time. I would try running it on straight alcohol and oil first. If there is no leaking, then you might try up to 5% nitro if you desire. If there is leaking it is not going to be an easy fix. The cylinder and crankcase can only be serviced with special tools. George Talent in the Tucson, Az area had some of the factory tools but he was getting up there in years the last time I talked to him several years ago. You might also ask around and see if Don Blackburn is still around as he might be able to service the engine for you.
Hope this all helps,
Mike