The earlier MDS engines may have had some problems, but I purchased an NOS .46 Pro BB that so far seems to run fine, turns an 11x7 with authority. With today's engines, there's nothing wrong with the sport plain bearing ones, even though they produce a tad less power than the more expensive ball bearing ones. Most get into problems when they run the engines in a too lean of a condition, so lubrication is reduced and engine runs hot, or runs with excessive load from an oversized or overpitched prop. Older cross scavenge baffle piston engines more or less have a power band that peaks at a lower rpm, require larger diameter or larger pitched props over the Schneurles. Over time, a person learns what or what not to do with particular engines. Even that $79 engine can be very satifying, provided that it is the right size for a particular aircraft, is properly broke in and properly propped.