Hi Gasayers, I too have had a bad experience with an RCV120sp. Mine was mounted on an old hack and promptly destroyed the thing!! I had run several tanks of fuel for breakin but nothing like the amount you did. The thing was put away after oiling for storage while I completed another project, well five years later I got it out to see if I could sort it out as I wanted to utilise it's compact shape to fit in a Spitfire. After consulting with Brian Winch of RC REPORT fame, I broke in the gears by using my lathe to spin the crank after removing the piston and rod. It took about two and a half hours with the use of toothpaste at first and then synthetic oil before I was happy with the way it turned over. After reasembly it was bolted to my strong test rig I use for my big gas engines and fueled up with an all synthetic fuel with 10% nitro as reccomended by Brian Winch and RCV on their web site. It started fairly quickly but I had to stop it because the header came loose immediately in spite of being well tightened. I have never been able to get it to run again!!!
I can honestly say that I am not going to put a motor with so many issues into a model that I have spent a lot of time on because I know what will happen. Another member of our club who is vastly more experienced than me has been unable to solve the excessive vibration and has consigned his to the history bin! It seems that the model flyers are being used to "develope" this motor instead of the factory getting it sorted, guess it's cheaper that way! Anyway, I now have an OS going in and I KNOW that will be OK. Numancia