07-19-2007 Ask Mike! Archive
Landing gear scissors

Mike;

Last March you did a right ruddervator bushing replacement and balance check on my J-35. Excellent work; fast and efficient! My AP now thinks I need to replace the bushings on the main and nose gear scissors. Although I trust his judgment, I would like your opinion as to when these bushings should be replaced and if there is physical evidence e.g.. bad tire wear to suggest that bushings should be replaced?  Thanks Mike. I plan to bring my plane back for some other work if I don't sell her!!

John


Hello, John

Tire wear would be an indication that the bushings have been well worn out. A replacement is definitely due then! Most of the time, this is a judgment call, hard to make over the internet. (There is no real published spec on allowable play.) I do know that when compared to other makes, such as a brand C nose gear, the brand C's will shimmy up a storm with very much play in the scissors, while a Bonanza will glide down the roll-out without exhibiting the same behavior.

I have found the most wear in your type system is caused by lack of proper lubrication. The big wear points are on the flange of the hat bushings pressed into the gear. I have discussed this in the past with Arky Folk (of Delta Strut, also ABS advisor); what he has suggested (and it works well) is to remove the bushing and place a pre-determined thickness shim underneath the bushing flange, then reinstalling the bushing 90 degrees (rotating) from it's original position. This will take up the flange wear, as well as giving a fresh wear surface inside, as these tend to egg out a bit. (One word of caution: confirm the ability to grease if rotating the bushing; you may have to drill an additional lubrication hole in the bushing prior to reassembly.)

When greasing the zerks on these parts, it is important to note where the grease extrudes out from; if it only comes out the free (open) end around the pin, then the grease is not necessarily getting onto the flange, where it is needed. Often, this can be alleviated by removing the pins and then the scissor, and simply cleaning the area of built up crud from years of service. This will also allow you to better find out what kind of wear your bird has, and better allow proper decision making for repair.

Gear Green,
Mike