when my main shaft bearing became notchy from a tip over crash i replaced it with the JR equivalent at $11.98/pair + shipping (rchelisplus.com)
Having done a lot of interviewing and info reading whilst rebuilding my Hyper 50 and selecting a set of ceramic ball/composite retainer type bearings I did have a long discussion with one of the Boca sales reps about the practical uses of each type of bearing they offer.
The ceramics are particularly designed for very high rpm, high heat environments. The prime advantage of them over a steel bearing is that the balls won't micro-weld themselves together as a result of rust or metallic contamination. This makes them excellent candidates for engine bearings.
The rubber sealed bearings offer protection from outside debris, but are more difficult to lubricate. The only area I'd ever cosider using one of these would be on the tail output shaft since the tail typically accumilates grass and exhaust residues.
If you keep up on keeping your heli clean and properly lubed, the more expensive ceramics are technically overkill and while some people can afford it, it just adds to potential crash costs.
The way I test radial bearings is I slide the appropriate sized shaft through the inner race and twist the bearing against the shaft to side load it and then rotate the shaft and/or bearing to feel for any hint of notchiness or grit. If I do feel some grit, I'll soak it in tri-flow and blow it out, if it doesn't improve, it gets replaced.
- Dan Goldstein