OS FT120 Gemini II first run 

Thank you very much for your kind comment, I'm really appreciated for that. Thank you and have a nice day !

Thank you very much for your comment, appreciated ! Working on it...

Thank you very much for your comment. appreciated ! Bit that isn't all, there are a few other engines from O.S. with FT markings, so, please, stay tuned ! And there in not all with Gemini II also ! Thank you and have a nice day !

Thank you for appreciating my work, reviews like this let me know that my work has value. As for the plug / breather in the back cover of the crankcase, there are several variations of this design: In the first, early Gemini, there is a boss in which the threads are threaded and the screw is screwed in. In the Gemini II, only a boss remained, but there is no thread in it, located on the right, in the first third of the crankcase cover. I also have a FF 240 (well, practically a FF 320, like yours, except for volume and power), it also has a boss, and there is a thread closed with a screw. In this way, we have 3 engines for two with a bosses and a thread and a screw, and one engine with a undrilled boss only. I have another one from this series, FT 160 Gemini, but I haven’t been into it for a long time, i.e. I do not remember. Tomorrow I'll be again in my workshop, so I can look into it. What can be useful from our set of statistical data? Perhaps this screw is technological, i.e. somehow the OS was needed in the production process (in reality I don't think so). The second thing that comes to my mind is that it is very convenient to pour cleaning liquid, or a mixture, into this hole to flush the engine after the flight, given that the engine is fixed to the frame of the aircraft. If you imagine that you screw a typical valve into this hole - an OS nipple / breather, then flushing the engine after flights can be quite a simple task, and at the same time save an expensive machine from possible internal corrosion. Why doesn't the OS install this second nipple / breather during production? There are several reasons, economy, and an excess hole in the crankcase, through which the remnants of the fuel mixture with oil will be sprayed into the aircraft. I hope you can agree with my assumptions. Thanks and have a nice day ! B.T.W., here is and additional argue in supporting my assumption - the location of the second screw for the nipple valve/ breather is very good in terms of the direction of the flow of the flushing fluid, the flow will be directed from top to bottom, while passing through the crankshaft chamber. That is, flushing will be complete, bypassing all the engine parts /elements.

@@crazyengines88 Many many thanks for your exhaustive answer. What you wrote is very important for me. Os Engines had answered to me a few year ago that “this nipple was for in-house manufacturing solutions. So, your thoughts, I think, are the answer. Thank you 🙏

@@gtfiberboy8064 That you for your question and kind comments, definitely, the answer was found 👍

Wow, great news! Firstly, I wish you successful takeoffs and landings, and secondly, good, calm weather and clear skies! Good luck and success! By the way, what fuel do you plan to fly on? Thanks and have a nice day !

@@crazyengines88 I have some video up! Little low speed tweak to make but it yearns for the heavens. I'm using off the shelf Omega 15% in mine.

@@TestECull Thank you very much for your reply ! Good luck with your flights and have a nice day !

@@crazyengines88 I'll try to get someone to take video of it in the air!

Great ! It will be very nice ! Will wait for it !