New Tailwheel Leaf Springs too thick

How to keep the Cessna 170 flying and airworthy.

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Bruce Fenstermacher
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

Larry, sorry, I did not see you got the springs installed before my previous posts.

The spring pack come with 5 springs. If you had the original steel bracket which came on your 170A (see another variable this is a replacement bracket), you would have used all 5 springs. The later bracket only uses 4 springs leaving the top smallest spring off.

To be certain when you and I are talking a shim, is this the shim you removed to make your springs fit? Sounds like what you might be calling a shim is actually the top 5th spring.
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

For comparison my NOS L-19 kit spring pack has the following thickness

Top spring .196"
Second from top .247"
Third from top .262"
Bottom main .360"

Clearly the top spring would be good for a 170 in thickness and I believe I've seen this measure before.
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hilltop170
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Re: New Tailwheel Leaf Springs too thick

Post by hilltop170 »

Bruce Fenstermacher wrote:Larry................

To be certain when you and I are talking a shim, is this the shim you removed to make your springs fit? ..............
From a wear standpoint, to me, it looks like the shim riveted onto the bracket is there as a spacer to keep the lower edges of the lowest spring from contacting the fillet radius on each side of the bracket. With the shim there, the rounded edges of the spring pack will bear up against the sides of the bracket and cause virtually no wear.

If the shim is removed, the lower edges of the lowest spring will dig into the fillet radius of the bracket. The steel spring being much harder than the aluminum bracket could cause abrasive point-contact wear on the bracket creating a stress-riser which could cause failure in a short time.

I would be very hesitant to remove that shim.
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1951 170A, N1715D, s/n 20158, O-300D
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Larry E
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Re: New Tailwheel Leaf Springs too thick

Post by Larry E »

Good idea Bruce.
Here's what I just sent to Univair:

The C-170 assoc. administrators and I are trying to determine the CORRECT thickness of the main tailwheel LEAF spring for the Cessna 170.

NOT the L-19

I just got a set of your PMA'd leaf springs from Aircraft Spruce, and the longest (main) spring is 1.510" wide and 0.320" thick. Part number U0542106.

The spring I removed from the airplane was 1.520" wide and 0.320" thick. (essentially the same),

We are wondering if the 0.320" dimension is perhaps for the L-19?

In your database, do you have the C-170 OEM design thickness' of the tailwheel leaf springs?

Can you let us know what they are?

Thanks.


I'll let you know when they reply

Larry
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GAHorn
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Re: New Tailwheel Leaf Springs too thick

Post by GAHorn »

Adding up the two stacks presently posted, the L19 totals 1.065
And the 170 totals .968
A difference of .097 (rounded to 1/10 th inch.)
Not sure these measurements are conclusive.
'53 B-model N146YS SN:25713
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dstates
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Re: New Tailwheel Leaf Springs too thick

Post by dstates »

Bruce Fenstermacher wrote:
The spring pack come with 5 springs. If you had the original steel bracket which came on your 170A (see another variable this is a replacement bracket), you would have used all 5 springs. The later bracket only uses 4 springs leaving the top smallest spring off.
]
Bruce,

I believe the 5 springs were for the 170. The 170A only uses 4 springs. See images from the parts catalogs below.

The 170A has a rubber isolator (item # 113, PN 0442124) above the top spring where the 170 would have had the short spring.

Doug
170_tail_springs.jpg
170A_tail_springs.jpg
N1235D - 1951 170A - SN: 20118
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Bruce Fenstermacher
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

Doug, you are right. I’ve made this mistake before. :(
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Larry E
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Re: New Tailwheel Leaf Springs too thick

Post by Larry E »

Bruce
I just spoke with Rick at Univair.

He was kind enough to search through the data, and told me their drawings (he did not say Cessna OEM specs) show the thickness for the main leaf spring of C-170, C-170A and C-170B is 0.312".

It's a very busy day for him and he did not have enough time to search for the thickness of the other leaf springs.

An earlier e-mail to them gave me the thickness of the L-19 main spring as 0.375".

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c170b53
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Re: New Tailwheel Leaf Springs too thick

Post by c170b53 »

With regard to the shim/spacer .. lets face it, its not rocket science advice until Miles chimes in....sorry couldn't resist... again. :oops:
Jim McIntosh..
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Re: New Tailwheel Leaf Springs too thick

Post by GAHorn »

If one looks at the tailwheel bracket in the Service Kit SK70A52-4 which is what was intended for the 170, one will note that the bracket part number is 0512000-75.
The same PN is indicated in the B model IPC, and that bracket also shows that shim (PN 0512000-76, spacer).

However, the L19 bracket is an entirely different PN 0624151 or 0624151-10 which can be substituted on an L19.

The L19 leaf springs are known to be “thicker” than the leaf springs for the 170, although I don’t recall anyone actually measuring and documenting the exact differences.

I suspect the 0512000-75 bracket and the 0624151 bracket differ in order to accommodate that difference.

However, it’s well-known that many folks have obtained 0624151 (and -10) brackets to install on 170 aircraft in lieu of obtaining the 0512000-75 specified in the SK70A52-4. This may very well be why were dealing with these spring-stack fitment issues (Although it’s puzzling why 170 springs won’t fit into an L19 bracket since the L19 has a thicker spring stack.

I will contact Pete Jones over at Air Repair Inc and see if I can get him to provide measujrements on the L19 springs and see if he has any thoughts on this.

Meanwhile, I've looked at my B model as well as a salvaged bracket the Assocn owns and doubtless is original, they both have that shim. I've looked at the L19 IPC and the ones shown also have that shim.
The B-model model IPC also shows the 0512000-75 bracket and it also has that PN 0512000-76 spacer/shim, s previously mentioned..

I'm fairly certain Cessna has it there for a reason and I'm beginning to think it's the latter bracket that include it (if any ever did not) rather than the other way around.
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

I don't know why I hadn't done this before. I measured my NOS L-19 bracket to see what total depth of spring pack it could accept. This bracket though stamped with an L-19 part number is considered to be the exact same as that found on a 170 or retro fitted to the early models that originally had steel. My bracket is stamped 0642140 3. it also has what I think is a NAS 1630-211-1076
IMG_0620D.jpeg
On the inside forward bracket which may have some wiggle room if the AN4 bolts that hold it in place are loose, the measurement on mine as these bolts are set is .975" to .979". I could imagine a thousand or two if the bolts are loosened and driven as wide as possible.
IMG_0617D.jpeg
On the aft end of the pack there is no wiggle room. the space is set by a riveted shim on the bottom and the top plate held tightly and exactly in place by 10 AN3 bolts. Th opening on mine is .951" ±.001". If the spring pack is thicker then that you are not getting it in without removing the shim, or egging out the 10 holes on the top plate for the AN3 bolts and probably bending the end tab of the top plate.

You might remember the NOS springs that came with this kit measure 1.065. At .115" thicker there is no way that pack will fit without a very big hammer. And we have yet to find what is suppose t be a 170 pack that will fit it either.
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

Larry, what Rick told you is interesting. I gathered with my conversation with Jim Dyer last year Univair has their specs. and to the best of Jims knowledge they are correct. He did not go so far to say they would match a Cessna spec. And it is obvious he is willing to learn what the issues are and try to address them ahd hoping we can provide solid better information.
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Re: New Tailwheel Leaf Springs too thick

Post by GAHorn »

I wonder if we’re overlooking what is staring us in the face: Suppose Cessna made ONE bracket to fit BOTH airplanes.... but the L19 installation instructions have the installer REMOVE that spacer?
(Anyone have an L19 Service Manual? Or Service Kit instructs?)
This might be the simplest answer of all.

(There is a corollary when Cessna service instructions have the installer remove a spring in the ragwing fuel pump check-valve.)
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Re: New Tailwheel Leaf Springs too thick

Post by Bruce Fenstermacher »

To consolidate some data form the other 5 page thread we find some data points which I think are pretty good.

Gary noted that his 170 springs measured .190, .189, .254 and .313 top to bottom totaling .946". Miles noted that his old top three springs measured .180, .180, .235 and the main spring he knew from Univair in the 90s at .321 total .916" Either of these spring pack combinations would slip into my NOS L-19 #0642140-3 bracket opening of .951". Gary's pack would be perfect, Miles pack would be loose.

What we need is more data points to present to Univair. I'll put out a call for more data in yet another thread.
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Re: New Tailwheel Leaf Springs too thick

Post by n2582d »

Bruce Fenstermacher wrote:Gary, I said I thought we established that later L-19 brackets did not have the shim. I did not say my L-19 bracket doesn't have the shim, it does. ...
Bruce, I couldn't find where we established that. You may be thinking of this discussion where George mentions that the L-19 does not use shim p/n 051000-30 (C-170B fig. 29-10) on top of the tailspring leaf stack.

As I pointed out earlier, the L-19 service manual lists two part numbers (0642134 and 0642156) for the shim of this discussion depending on whether it was an early fishmouth bracket (p/n 0642140-3) like you pictured or a later one (p/n 0642150-10). I wonder if these shims are of different thicknesses.
gahorn wrote:I wonder if we’re overlooking what is staring us in the face: Suppose Cessna made ONE bracket to fit BOTH airplanes.... but the L19 installation instructions have the installer REMOVE that spacer?
(Anyone have an L19 Service Manual? Or Service Kit instructs?)
This might be the simplest answer of all. ...
George, I'll email you and Bruce the applicable sections in the L-19 maintenance manual. There is no mention of removing this shim. For added confusion--as if we need it--they write about aircraft modified to the 2800 gross weight configuration. With this modification they use five leaf springs. I have been unable to find any L-19 IPC which gives part numbers for this modification.
Gary
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