The International Cessna 170 Association

An A&P friend heard me say that I occasionally have a shimmy on my tailwheel. He asked me to raise the tail and take the weight off, then had me take my hands and move the tailwheel from center to the far left and then to the far right. I can do this with no resistance. He concluded that there is some part or parts that are worn out as I should be encountering resistance to "break over" the tailwheel. As I said, I have none. He thinks the plate (?) the steel balls fit into under the three small springs is likely worn out. What are your thoughts? If this is the case any suggestions as to what parts may need to be replaced when I overhaul the 3200?
I can't remember when I had any break over with this tailwheel. While shimmy is not a major issue, it seems to occur more often if I have a person in the back seat.

This is the parts list: https://www.airframesalaska.com/3200-Se ... -3200a.htm

When I did mine a couple of years ago I just bought a complete rebuild kit from Airframes Alaska. Saved a few bucks versus buying the parts individually and in my case clearly the only maintenance that had been done in forever was pumping some grease into it occasionally.

Here's a good series of YouTube videos that show a disassembly, cleaning, and reassembly:
https://www.youtube.com/watch?v=S-0i2MTe-A0
https://www.youtube.com/watch?v=8MGri0D50hg
https://www.youtube.com/watch?v=X1uAd0KSnCc
https://www.youtube.com/watch?v=3NDBrFY95bI
https://www.youtube.com/watch?v=3NDBrFY95bI

Thanks Brian, I had seen those videos a few years ago and forgot all about them. Interesting he recommends replacing the tailwheel to tail spring bolt every annual. One of these days I will order the overhaul kit and rebuild my extra tail wheel assembly.

Frank, you likely have a shimmy when you have a rear passenger because of the extra weight in the rear and perhaps, and maybe more likely the change in tail wheel king pin angle due to main spring flex.

In theory, we would all like to have no resistance moving the wheel side to side as you did. Of course because of variances in weight, spring flex thus king pin angle, the least amount of drag needed is best.

In the 3200, drag is caused by as many as 5 springs but in our 170s only 3 of the springs where used. This puts pressure between the thrust washer and thrust plate creating friction. This is what causes drag. The amount of pressure and resulting friction/drag depends on how many springs are used, how tight the king pin shear nut is and how much grease has been pumped between them.

While it is entirely possible your 3200 parts are shot. It is more likely you could clean the grease out of the thurst washer/ thrust plate sandwich and reassemble, and your shimmy would go away. If not then turning the shear nut one flat at a time tighter until no shimmy is encountered.

Like so many things there are two popular schools of thought on how much grease a tailwheel should have. Some say none and others, who point to the grease zerk say they wouldn't have one if it wasn't suppose to be used to pump the mechanism full of grease till fresh grease oozes out. I remember hearing the zerk is used to grease the bearing only but over greasing forces grease between the friction plates if over greased. That there should be no grease in the plates. But I don't recall the source of that info.

If I where you, I'd turn the shear nut one flat tighter and what till the next time you have a passenger in back and see what happens. Depending on your greasing habits, you might want to forgo a greasing or two as well.

If there is NO resistance... that leads me to think the pawl and pawl spring are broken or missing. There should be a “detent” which the pawl assy creates. Addt’l friction is created by the plates and 3 compression springs which is adjusted as. Bruce discusses.
It’s unfortunate that we’ve never been able to locate a copy of the Air Force manual on this tailwheel. As far as I’ve been able to determine the Air Force/Army had a technical manual which I’ve found reference to in other pubs, but never been able to lay my hands on. However, this Scott 3200 is not really a mystery when it is in new/ovhl condition and most difficulties occur due to worn parts and incorrect assembly of it and the mainspring/stack assy.

Frank-
It's very easy to disassemble and reassemble the tailwheel. Take it apart, inspect everything, replace worn or missing parts, and put it back together. No problem.

I agree with George, the pawl and spring would be my first guess and if they are bad, most likely other parts are as well.

Alaska Bushwheels has bins full of every part you might need.