This is a well used OS 120 4 stroke Circa 1983. I've been flying it on a Sig 4*60 for a while but prior to that I was flying it on a 4*120. It flew both airframes very well (still flies the 60 just fine).
I use a 15x6 or 15x8 Zinger on it with about 10% nitro fuel. Nothing fancy; it runs like a sewing machine basically and I love it. I'm reticent to part with it as it also makes a great display engine. Make no mistake this is probably my second favorite engine (my first is a rather run of the mill OS 70 Surpass II).
It has been well cared for, well run and in between uses well stored. It is a nearly 30 year old engine however so it does show some wear and tear. I will take some pictures this week and post them to the ad for reference. It has good compression and runs well today. Parts are hard to come by on this engine so I would plan on being careful with it. It's not a power house - remember - Circa 1983 and as such it is one of the first great running OS 4 strokes. Freshening up with a new ring and new bearings probably wouldn't hurt but I have been very happy with it in my 4*s and so I have not done those things.