Rumbling Bearings
Hi Folks,
hope that you can help me understand what's happening to the bearings in my OS91FX. The story goes ...
1. bought new NTN bearings (exact dimensions of the originals), removed the seals except for front seal on front bearing, and cleaned all the lubricant out with petrol.
2. put bearings in the freezer, applied a little heat on the crankcase and dropped them in without need for any force to make them seat properly.
3. lube them up with a little castor oil - smooth a silk.
4. run the motor (fly the plane) on 15% LV Synth (heliglow) + 6%castor + 5% nitro and the bearings feel silky.
So far so good ... all seems well until ...
I store the plane for a month (I'm not in a humid climate) and now the bearings feel notchy, in fact the motor is slightly locked and needs a little force to turn the crank whenever it sits for extended periods. The notchiness reduces when I flush the engine with fuel but it doesn't feel silky like before. There's a definite rumbling feel to them which you can detect through the crank shaft and hear if your ear is close to the motor. The engine still runs really well but I'm not happy with my new bearings. This problem does not opresent it self with other engines using the same fuel with the same brand and type of bearings (eg. OS46FX and OS40FSR). I don't use after run lube (ATF) unless I plan on parking the engine for several months.
What have I done wrong? Are the special bearings that I should have bought? Should after run be used ALL the time?
Your advice will be appreciated.