I have bought a few used glow engines on the for sale Marketplace here and have been disappointed . The last purchase was a Super Tiger 90 Glow listed in good condition . The engine I received was very hard to turn over and the bearings were very " notchy " feeling . I took off the engine backplate and head only to find a lot of rust from the engine sitting for a long time with fuel residue . Although the standard practice in RC boat racing circles , after run oil does not seem to be a regular practice in the airplane crowd . I have been flying and boat racing since 1980 so over that time I have had dozens and dozens of different engines and installed and replaces many many bearing due to use and neglect . Lube the engines up if you are not going to use them , glow fuel is very corrosive and will hurt the bearings if left to sit .. I will have to rebuild the engine I just got from Marketplace . Buyer Beware !