dkshema
rrProfessor
Location: Cedar Rapids, IA
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| I don't remember reading bearing complaints before the Hyper 50 head was introduced..
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My 50 SX-H goes through rear bearings about as often as my Hyper. It's not the head.
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About preloading -- from the limited reading I've done in the past couple of days, it would appear that in order for preloading to be a useful practice, the bearings themselves need to be designed FOR having a pre load put on them. I recall seeing something about the balls and races needing to be designed for the task.
Further, it appears that unless you really do the pre-load correctly, bearing life can actually be shortened, as you build up heat in the balls and races.
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Perhaps yet another contributing factor would be the heat seen by the motors. As with most other man-made items, heat is not your friend. Thermal expansion, the delta between the temperature of the outer race vs the inner race and the effect of heat upong the bearing steel itself all can have detrimental effects upon bearing life. This would also make the "Coke can" mod a dicey fix, as first of all, the bearing may not be designed for a pre-load, you really don't know if the thickness of the shim is correct, and you have no real control over thermal expansion and temperatures of the bearing.
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More reading about ball bearings indicate that these little beggars are actually pretty finicky about how they are treated throughout their life. It would appear that the races are easily damaged, and the damage does not have to be severe to limit their useful life.
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I believe that the bearing is simply being asked to support way too much of a radial load due to the forces on the piston, rod, and crank caused by the combustion process.
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Mr. OS had to make a compromise when the 50 SX-H was introduced. He was constrained by the need to retain the outside dimensions of the 46 crankcase while being asked to dramatically increase the horsepower of that same basic motor. The YS 50 people, and even the TT Redline folk both see the need to retain those same outer dimensions (to remain as a viable alternative to the OS). The size constraint, coupled with the need to produce gobs of power force a compromise in the design.
Take a design that is less than robust due to market constraints, then sell into that market where people start running 30% nitro coupled with aftermarket exhaust systems that extract even more horsepower from the powerplant, the weak link will be revealed again and again.
That link is the rear bearing. Probably not by choice, but because it's the result of a compromise between good engineering practice and market forces.
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The bottom line would appear to be that we will continue to have rear bearing problems in the high performance 50's, and we simply need to learn how to identify the need to replace the darn thing before it gets puked out the exhaust port.
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* Making the World a Better Place -- One Helicopter at a time! *
Dave |
Having said that , I haven't had any real problem with bearing failures ,my OS 50 heli engine has now done three seasons on its original bearings , but I have had to replace a set in one of my OS 50 aero engines .
