Thanks for your confidence in me.
Here’s what I want you (and your mechanic) to do.
Remove the nose tire wheel assembly and balance it. Then re-install it and see if your problem disappears.
Here’s my line of thinking. I suspect the tire/wheel is quite far out of balance and that it is tending to shimmy but not quite far enough out to shimmy all the time. But every 1 out of 7 times it hits a discontinuity in the runway, or when you apply the brakes unevenly that exacerbates the out-of-balance condition and it starts shimmying.
When you tightened up the linkages it didn’t stop the incipient shimmying, it just better transferred that slight motion to the rudder pedals/airframe.
If your mechanic doesn’t have a wheel balancer–I bought a slick little tool box sized one from McFarlane Aviation (www.mcfarlaneaviation.com; ask for TOOL108) that I use to balance all my tire/wheels.
If your mechanic already has one, that’s great.
If he doesn’t have one and you’re reluctant to spend the $200 for a McFarlane one you can balance using this “bush mechanic” method.
Remove tire/wheel/axle from the airplane. Clean all the grease off the bearings and bearing races. Clean!
Reinstall the bearings in the races and install the wheel assembly on the airplane. Spin the tire/wheel by hand. Let it spin down until it stops. The heavy point will be down. By trial and error, place tire weights (get them at an auto parts store) on the wheel until the “down” spot of the tire/wheel assembly is random. When you reach this point, your tire/wheel assembly will be balanced.
Finalize the weight placement, grease the bearings and re mount the tire.
Please let me know if this has solved your shimmy problem.
