Brad Brady wrote:.....my criteria is holding the right side.....if you can move the left more than an a half of an inch (Outside control wheel).....I'll change both......( after I am certain that the chain and cables are correct) there is no reason to change just one side......
I can appreciate what you are thinking, but to be slightly more cheapskate..... what I believe is a better method is to lay under the panel and, while looking up at the u-joint, and while holding the sprocket in one hand,... operate the yoke to determine the freeplay in that one side, then compare it to the other. In that fashion, one is actually determining the relative looseness in each yoke/u-joint assy rather than the total looseness. (If one were very loose and the other tight, would you want to replace both?)
Also, don't forget that the u-joint also transmits push/pull inputs to the control system. Simple twisting movement is not it's only ...in fact is not even its most stressful.... function. Make certain there is no excessive fore/aft looseness in the system which might indicate wear. While under there, look for any indication of wear or runout in the bronze bushing inside the "T".
What actually causes looseness, anyway? Well, certainly wear does, but what causes the wear? This is a low-stress system and that u-joint does not operate at high speed or high-operating stresses, so what wears it out?
I believe that two things contribute most of the wear over the years. The first contributing factor is vibration. That u-joint sits on the end of a long arm (the shaft) and with the vibration of engine/airframe being magnified by that long arm, wear is accelerated at any point of contact that has materials-change and/or attachment. That u-joint is just that sort of device.
While the bearings are hardened against that wear, they receive the benefit of that vibration nonetheless, and our hand resting-on-the-yoke at the opposite end adds upward pressure to the joint which may increase the hammering effect of vibration. (It may also be that a yoke that is completely free to vibrate at the end of the shaft, such as the copilot's side normally does, might receive wear from this factor.) Either way, things are going to get loose eventually. When the original u-
joints are replaced with modern equivalents, they are usually replaced with the MS 20271 types which have protective covers incorporated, which provide some of the benefits Jim and SeniorChief may be seeking. I'm reluctant to endorse garden hose unless it met traceability requirements.
Another factor is the type of control locks that most light Cessnas have. Most Cessna control locks hold the control wheel/yoke and the rudder pedals. If you think about it, that means the control surfaces, when deflected by wind or other input, pass their movement on to the control cable system, which ends up at the cockpit control wheel/rudder pedals. While the factory method may protect the control surface from banging against it's stops....all that abuse from wind also abuses the entire control system....the cables, pulleys, each bearing, every contact point,.... and each u-joint.
Even the C-170 whose owner uses the seat belts to hold the yoke (like me), suffers similarly. The best systems use a method of holding the control surface externally. (However, as most of us know, do NOT lock the rudder to the vertical stabilizer at the counterbalance area or you risk serious damage to your rudder. Use a bungee or rope system that holds the rudder at it's trailing edge, instead.)
Another method by which the system receives wear is through ill-informed lubrication methods. The aileron control-chains are normally not lubricated with oil, so that they do not attract dust/grit to cause wear. They are normally only wiped with a clean dry cloth, unless the airplane lives in a really humid or coastal environment. (I consider outdoor storage in most of the U.S. to be that sort of environment. In such cases, a light spray of lube oil such as LPS-1, followed by wiping with a dry cloth is what I'd recommend.) The early u-
joints had exposed bearing/
joints and should be lubed with light oil. Same thing for the bronze bushing whithin the control "T" thru which the sprocket driveshaft passes. The oil recommended is Mil-7870, but any light oil such as 3-in-One, sewing-machine, or gun-oil is suitable.
Anyway, I was just provoking some thought on how our systems actually receive wear through 60 years of service.
I do not plan to use any different lock-system on my aileron/elevator system, but I do inspect my control system thoroughly at each annual.
