Thanks for the info so far, I guess to narrow the question; Are there any brands you should steer clear of? I've been running a O.S. .40 FP in my Midwest AeroStar for some time now. I want to buy a Sig Four Star (60) or Venture 60 next so I will be looking .61 size.
Another Question: Is the O.S. .46 AX ABL that much better than the .40 LA to warrant another $50? If my buddy had the money, should he upgrade to this motor for his Trainer?
With regard to two-stroke motors, particularly in the .40 to .60 size range, a few generalities can be made:
O.S. and Thunder Tiger make top quality engines in this size range. They are not particularly high compression engines, which makes them less sensitive to fine tuning and thus easier for beginners to operate. They will fly best with 10% to 15% nitro fuel, will operate best with a hot glow plug, and both manufacturers recommend castor oil as a significant part of the fuel's lubrication. Both manufacturers feature ball bearing (O.S. FX, AX, SX or Thunder Tiger Pro) engines or bushed engines (O.S. LA or Thunder Tiger GP). Bushed engines from either manufacturer should be operated with a minimum of 18% oil content fuel and 50/50 castor synthetic blend. Ideally, O.S. LA or TT GP engines should be run on 20% lubrication all castor fuel.
Super Tiger, Magnum, and Evolution two-stroke engines are generally regarded as very good engines, but not perhaps as high quality as O.S. or Thunder Tiger. These engines are higher compression than comparable O.S. or TT engines, and are thus a little more sensitive with regard to fine tuning. These engines will run quite well on 5% or 10% nitro, and even straight methanol/castor fuel could be used for longer flight times when power isn't critical. These engines may require a medium hot or medium glow plug instead of a hot glow plug, particularly if used with higher nitro content fuel (15% or higher). All engines by these manufacturers feature ball bearing construction, there are no bushed engines in their line-ups. All of these manufacturers also recommend significant amounts of castor oil as part of their fuel lubrication.
Other engine brands in the .40 to .60 2-stroke marketplace include GMS, Tower Hobbies, SK, JBA, Aviastar, Webra, MECOA, HP, HB, Aviatronics, and a number of others. Some folks have great experiences with these engines. Others have trouble getting them to operate smoothly or have difficulty obtaining service or spare parts. Then again, some folks have problems with O.S. or Thunder Tiger engines and are frustrated by them despite their best-in-class reputations.
The simple truth is, while 2-stroke engines vary a bit with regard to fuel and glow plug requirements, most every brand of .40 to .60 2-stroke sold today in North America is a good servicable product that should perform well for the owner. A new pilot would have to search long and hard for a truly bad engine.
Dollar for dollar, the best sport engine on the market is probably the Super Tigre GS-45 ABC at $64.99. I'd buy it over the GMS, Tower Hobbies, or most any other brand out there. I don't think it would be a mistake to spend an additional $45 to buy the O.S. .46 AX however, I own three of the O.S. .46 FX/FXi engines that preceeded the AX, and they're delightfully powerful, reliable, and easy to start and tune. If you have the money, buy the O.S., but if you don't then buy Thunder Tiger, Super Tigre, or Magnum (in that order).
Happy shopping.