Soooo, after removing my old spring I found what looks to be a real backyard repair. the last two inches or so had been cut or broken off and the main bolt through the Scott tailwheel to spring was actually going through two leafs!!
you can actually see the rough edge of where the leaf had broken... they seemed to have just drilled another hole through both leafs and mounted the tailwheel!
so of course the new bolt I have is WAY too long
oh, very glad I went with replacing the entire pack after pulling it apart.
The repair you found is not so odd. Yes it looks bad when compared to new. I think you will find more 170s with this type modification than you would expect. I've seen a few and I've owned one that used two (full length) main springs.
First, I wouldn't be surprised if this repair was made 50 years ago. A different time. Folks made things, repaired things and where not afraid to improve a weak design. And lets face it, this is a weak design. Do you think these springs just started breaking or do you think they've been breaking with the same failure time since '48. Do you think a guy in '50, after a failure, specially one that destroyed his rudder and maybe an elevator, was going to be satisfied with changing a perfectly good spring out at 500 hrs. Hell no.
And they didn't have to look far for what to do. Piper products like the Cub they flew in the war have two main springs the tail wheel attaches two.
I've told this story before. My first 170 had 2 main springs. Took me a while back when I was just learning the 170, to realize I had 2 and wasn't suppose to. Going firmly against George's recommendation to remove that "dangerous" setup, I did not. I flew it that way for 10 years until the plane was wrecked in a micro burst on the ground. George felt that the 2 springs when bent would act like a shear and cut the AN-7 bolt holding the tail wheel on. I could see his point but the AN-7 never showed sign of shearing action.
Coincidentally I just removed the spring pack from my Cub yesterday. It had been a while and I need to rebush the Maule tail wheel and (every body take a breath) rearc the springs a bit. Low and behold the top spring of the 2 that hold the tail wheel on is slotted at the fuselage attach point. What this means is the 2 springs can bend independently for about a 1/4" and then impart a shearing action on the AN-5 bolt that holds it on. Interesting.
Back to our 170s. I do not recommend running 2 main springs. And while it is tempting I have not installed that configuration on my current 170. Of course legality is an issue but more than that is the failure rate of the bracket the spring pack attaches to is just to high. I wouldn't be surprised to find a 50% rate of 170s in a group with a crack somewhere in this bracket or the top plate for it.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Finally got it back together. No easy feet I might add. These new packs are just a bit bigger so negotiating them in takes some time. I did not reinstall the shim that was on the original one... No way that would have fit.
I'm surprised how much more flex I have and tail height is noticeable just looking at it.
Having to add 6 links to each chain tonight to make it reach( I hope)!
I noticed on a few other planes on these threads have the upper channel plate bolted on. Mine is riveted.
Bruce I did read that discussion on using two leafs... In my case they actually made an insert bushing for the tailwheel bolt. That was in really bad shape though. Who knows how long this Canadian certified plane has been this way
You should see another 170b ramp mummy tail wheel setup at our field...
swixtt wrote:
I noticed on a few other planes on these threads have the upper channel plate bolted on. Mine is riveted.
Riveted in. The spring packs must be put in compressed together in a stack and just fit tight. And not the easiest task with the top plate removed. I likely wouldn't have unmodified yours and drilled those rivets out.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
First, I wouldn't be surprised if this repair was made 50 years ago. A different time. Folks made things, repaired things and where not afraid to improve a weak design. And lets face it, this is a weak design. Do you think these springs just started breaking or do you think they've been breaking with the same failure time since '48. Do you think a guy in '50, after a failure, specially one that destroyed his rudder and maybe an elevator, was going to be satisfied with changing a perfectly good spring out at 500 hrs. Hell no.
500Canadian hours or American? i'll go get the popcorn.
Well I gave my king pin nut a half turn and gave it a try... No more shimmy after a few wheelie and three pointers. Hopefully I've got it under the right tension now. Hard to know when turning the tail wheel assembly by hand.
I hope you meant a half turn farther than it had been cause I'm pretty sure just a half turn won't engage the king pin enough to stay on long and make inserting the cotter pin a real bitch.
Yes it it hard to figure the right pressure or adjustment of the nut by hand turning the wheel. If I was installing the nut with no reference what worked, I'd spin on the nut so I could just insert the cotter pin or the loosest adjustment. Then I'd tighten it half turns if required.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
after blowing off the dust and cobwebs, i found this from the deep recesses of TIC170A interweb ...
My tailwheel shimmy went away when I replaced the old tire and tube with new ones. However, for those that might still have the problem, I found this in the Cessna Service Information Summary ( 1946 thru 1962 )
Date: 10-24-50
"We have had some reports on Scott pneumatic tailwheels shimmying. The Scott 8" pneumatic tailwheel is designed with a friction type shimmy dampener. This friction is regulated by 3 small compression springs inside the upper casting. If the main king pin nut becomes too loose the shimmy dampener effect will be lost. When the shimmy occurs, it is recommended that the large nut be tightened in increments of 1/6 of a turn until the tailwheel starts to bind when rotated by hand. Then back off 1/6 of a turn for correct tension on the shimmy dampener. The king pin nut is on the underneath side of the lower housing directly above the tire. This procedure will definitely assure that compression springs in the dampener are acting against the friction dampener disc. We recommend a tire pressure of 30 pounds on both the 140 and 170 for the 8" pneumatic tailwheel. When connecting the springs and chains on this assembly, it is recommended that the stretch in the springs be from 1/8 to 1/4". The springs used with the 3200 assembly have a high tension rate and if stretched to any extent on assembly the mechanism may not release easily. No slack should be left in the chain and spring hook-up when both sides are connected."
A note on the 3 springs. Many 3200 tail wheels that could be found on 170s have 5 springs. Doesn't matter. Adjust the nut so there is no shimmy and no more.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
that is right... the upper thrust plate has three fix pins for three springs and the remaining two springs do not have pins on the thrust plate. lighter planes run three, our 170's run five.
speaking of that plate, is it easy to get out? when i was in there last i couldn't remove it for some reason. i cleaned up everything else and put it all back together again. next time i'm in there i want to replace it.
