Univair tail spring

[c170b53]

Well sorry to say that’s all wrong somewhere. I wouldn’t use the plane until we figure this one out as all you’re going to do is damage your parts. There’s a little pad right below the main spring to prevent the main spring from contacting the corners of the fish mouth. The main spring should be in contact with that pad at all times. So I would lift and shore up the tail and see if the main spring comes in contact with the pad. Just guessing that the bushing in the forward attachment point is missing and likely the bolt is bent. Buy the spring pack from Univair, it will fit and check that nothing else is damaged. Replace all the bolts, it’s easy work and whomever got you into this spot needs to read our forums a bit more please.

[c170b53]

The good news is your spring retaining plate appears to be in the right spot. A few pics, as you have it taken apart and the collective group here should be able to sort this out.

[Buckeyejim]

Bushing is in place in the front holes in the leaves. Bolt and nut are new. The 3 leaves in the picture
are part of the 4 leaf spring set I bought from Univair a couple of weeks ago.

[c170b53]

And the forward spring block has the v groove facing up?

[johneeb]

And the forward spring block has the v groove facing up?

I think the arrow points to the spring block Jim is referring to and it would definitely upset the apple cart if installed upside down.

[c170b53]

Thks John, guess I didn’t describe that well but your pics are just what’s needed.
Sorry Buck For some reason I thought this was all new to you but in fact you removed 4 springs and couldn’t re- install four new ones. You’ve done the right thing and renewed the hardware, now it’s just refitting everything. And I guess you’ve compressed the spring pack together along with the spring retaining plate and is it at this stage that the an3 bolts cannot be installed?

[sfarringer]

Might be interesting to actually measure the thickness of the leaves in the old spring set, and the new spring set....

I think I can find my spare spring set, and measure it for comparison.

[c170b53]

Here’s my set-up and I think it does show my spring retaining plate higher up in the fish- mouth than Buck’s set-up (photo )

[Bruce Fenstermacher]

Unfortunately by this time the original parts, NOS and so many variants from the L-19 adding in parts manufactured and sold as replacements, it would be hard for anyone to say with certainty they have the exact dimensions of the springs that left the factory. I'm 100% certain Jim Dyer believes he is selling duplicates of the original. Of course Jim may have the original Cessna prints he believes are original and yet recently Cessna themselves have said they have no evidence they ever made a part in a certain way (the stabilizer bracket), yet I think we've proven without a shadow of doubt with a survey of installed parts, they did.

From your picture the main sprint is thick, the middle spring is thick and the top spring about what I'd expect for all the springs in a stock 4 spring pack. And this, and maybe some other reason is why you can't fit all 4 springs. I ran into this myself about 15 years ago. Notice I didn't say any spring was to thick just that they are thick. There are 100s of 170s with a 4 spring pack with a thicker main spring. I think the combination of your two thicker springs is the issue.

[n2582d]

Might be interesting to actually measure the thickness of the leaves in the old spring set, and the new spring set....

I think I can find my spare spring set, and measure it for comparison.

Here’s one data point.

My L-19 main tailspring measures 0.348” thick. I measured the opening which the tailspring assembly fits in at 1.023”. The shim riveted to the base of the bracket where the springs exit is not listed in the C-170B IPC but in the L-19 IPC it’s shown in fig. 54-34 as a “tailwheel bracket spacer”, p/n 0642134 on the early models and p/n 064215X on the later models. (Can’t read the last digit on Air Repair’s IPC). That shim or spacer measures 0.056” on my plane. My top three leaves are not yet painted but as they are now I calculate that I have 0.078” loose fit using the new Univair main spring and 0.043” loose fit if I reinstalled the L-19 main spring. The other interesting comparison between my new Univair main spring and the L-19 spring is the angle of the rear bend. On the Univair main spring the bend is 9.5°, on the L-19 spring it is 17.7°.

[c170b53]

Splitting shims here, but I think the shim is depicted in the 170 B IPC but does not have a P/N call out because its part of the fish mouth assy.

[n2582d]

Jim,
That's right. Is that shim or spacer there to fill in the gap that would be there if the springs actually laid flat on each other or is it there to keep the main spring from wearing into the radius of the bracket?

[Bruce Fenstermacher]

Gary, could you make it more clear the source of those red measurements in on the drawing. Did they come from Cessna drawings of 170 parts? Cessna L-19 parts. Actual measurements of on hand springs thought to be original 170 parts, L-19 parts or parts manufactured to match within tolerance of the previous pars mentioned?

[Buckeyejim]

At the bottom of page two I said that I thought the three springs were the same thickness. So much for my powers of observation - they're different.
I measured the combined thickness of the 3 lower leaves in the 4 leaf stack I bought from Univair and got .810". That contrasted with .640" for the
three bottom leaves that were in the plane. I plan to insert a thin aluminum shim below the bottom leaf and go with a 3 leaf tailspring.

[n2582d]

Bruce,
Sorry I wasn’t more clear. The main spring comes from Univair. The top three leaves and the thick mainspring- which I assume is an L-19 leaf - came with the airplane. Original or correct? No idea. Like I said it’s one data point. It would be interesting to compare these numbers to what others have. The only way to find out what the original thickness was for these springs is to buy the blueprints from Cessna. I’m curious, but not that curious.