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Please help with nose wheel vibrations

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20 Mar 2019 21:34 #1882 by Gene Bunt
Replied by Gene Bunt on topic Please help with nose wheel vibrations
I have found that uneven wear on the nose wheel will cause the shimmy. However the coupes I have did not have a fork it had the one side with the single ball bearing. The uneven wear could be caused by a balance problem. The side load pressure on landing in a crab also causes uneven tire wear. On both coupes I had and have. changing the tire eliminated the shimmy. Since these tires are expensive I plan to send my old tire to have it re-treaded.

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18 Mar 2019 09:45 #1876 by Bob Thompson
Please help with nose wheel vibrations was created by Bob Thompson
This may turn into a series of posts as I evaluate specific details but I am looking for some help on the famous nose wheel shimmy / vibration causes and solutions. First, I have read all the summary articles on what to look for and have addressed with my mechanic most of them but there are still a few details I can not find online.

I have owned the plane for 1-year and never experienced this until I picked it up after annual. Initially we noticed that the nose wheel had less play in it than before due to the main nut being reinstalled a little tighter. this was loosened and the issue when away for 4 take-offs and landings...3-days later is showed back up but much milder than the original shimmy. Next we inspected the wheel itself and found severe flat spots, uneven tread wear cracks from age so shimmy or not it was time to replace. That was done over the weekend with a new 5.00-4 which also behaved the same way on rotation...vibration as the weight was coming off the nose wheel.

One detail I can not find a quantitative answer to is exactly how tight or loose the nose wheel nut should be. I understand (maybe incorrectly) that there should be a good amount of movement of the wheel that was intended to aide in x/wind operations in the original plane. Is there a spec tolerance to determine the limits of this movement? Also, I have rudder pedals and can control the rudder independently from the nose wheel...would this imply that my wheel nut should be tighter since using the rudder I can eliminate all side load from the wheel above about 40-MPH? I have not flown the plan any differently than over the last year and I can't find any mention or mechanic's memory of adjustments made to the steering rigging; if I can find a spec on how tight the nose wheel should be, that would help in this process.

THX

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