RE: OS 46/55 bearings bad again!
TTpro 40 engines USED to eat rear bearings in 424 Q500 racing. I've seen several that have been ruined when the steel bearing cage came apart, sending pieces up through the piston and liner, including one of mine that I thought I could get one more race out of, before I changed to bearings with the plastic bearing retainer cage, rather than the stamped steel parts.
I haven't bought a new TTpro 40 in a couple of years now, but I have heard that they are now coming with bearings with the non-metallic cages. Of the 4 I have, one failed before I got the bearing changed, the others were all changed when they were brand new.
We're running quite a bit higher RPM in 424, typically 16,500-17000 on the APC 9/6 prop is where they'll peak. The steel cage bearings would just come apart under those conditions.
So - if you do switch to TT engines, you might want to check those rear bearings - if they're stamped steel cages on the balls, I would suggest changing them before you even run the engines. I bought most of mine (and the ones I did for others in the club) from RC-bearings.com. We bought stainless ones, and so far so good. I've heard the plain ol' steel bearings (not stainless) are actually harder and more durable, but you do want to be a little more conscious about running the engine dry and using sufficient good after run oil to protect them. Having some castor in the fuel seems to help.