After some looking through my messy file I did find the paper work on our OS engines.
Remember, I have't looked at this stuff for years and I didn't have this quite right.
I got this information off a old torn out yellow page of High Flight Quarterly newspaper.
Some information for owerners of OS FS102 (old style), FT160 twin engines. The early OS 120 engines that are marked with the letters RP under the engine mount lug are somethimes prone to a case separation at the rear crankshaft bearing. If you have one of these engines, carefully inspect the outside of the crankcase around the rear bearing boss for cracks. Some of the O.S. FT160 twins have a possible defectiver connecting rod set. Check the serial number stamped on a small machines flat at the bottom of the crankcase, just behind the carburetor. If it matches one in the series listed below, again, contact you're dealer.
The serial numbers are: 000105-128.....130-189......191-236.....350-473....493-672....001050-1052
The engines beginning with serial number 001096 and above are all O.K.