guys, have some question regarding changing engine bearings.

all these while i have been using original rear inner bearings, but for the front bearings, i always use those aftermarket bearings bought from bearing shops. but my set of bearings always lasted me for max. period of about 3months, only on weekend racings. May i know if this combination is the cause of damaging both my bearings which leads to shorter time span? also do u always replace both bearings together? or just inner bearings? thanks. if the max power bearing removal tool useful as i always heat up the engine and bang it on the desk to get those bearings out, the same for installing new bearings (i put in freezer for a while for it to sink 1st), then heat the engine and stuff it in.

other questions :
- how do u determine engine is damaged?
normally, we hear the loud crashing noise. then vibrate the crankshaft to see if it moves. so is this the appropriate method? wat would happen if we continue to run the engine w/o replacing bearings

- will damaged bearings causing engine difficult to tune?
coz yesterday, while running the car (it was fine at 1st), my 2-speed doesn't want to change, so i lean it by 1/2 turn, but still it doesn't change. then bringing in my car, i realise the bearing noise and the bearing got loose (from vibrating crankshaft).
have another engine, which was fine all these while, but strangely, need to return everything. coz when u go from straight long road, into very deep corner, where u have to brake it hard, it just died off. (tried almost 10times, died off at the same spot) would this be the cause of engine bearings?

kind of disappointed with both engine needing to replace bearings. hope some1 can share their thoughts.