Engine cowl & Tinnerman nutstrip

[Karl Towle]

I'm putting the following information in the forum, in the interest of saving someone else a few frustrating wasted hours.

Restoring a '54 170B, the Tinnerman nutstrips used to secure the lowest five(5) screws on each side of the engine cowl, were in sad need of replacement. After some searching, this nutstrip was found on P36 of the parts manual, as 19-23, and again on P38 as 20-21. These references show Cessna part number 0513000-20.

These nutstrips, secure 5 screws per side, and each have an additional 3 "blind" screw holes. So they are actually 15.5 inches long, and riveted in place by flush rivets located mid-way between each Tinnerman clip (with one rivet closer in at each end). Not wishing to drill the 16 new holes required to replace these strips with individual Tinnerman plates, I sought a source for purchasing the original nutstrip. I found out right away that Cessna had superceded the part number to SK170-13, so I ordered two, for a painful $19.17 each. Imagine my surprise when I opened the box, and found - you guessed it - two bags of neatly packaged individual Tinnerman plates, rivets to mount those plates, separate rivets to fill the existing holes and documentation for this "service kit." Further, a SINGLE kit was sufficient to replace the nutstrips on BOTH sides of the fuselage.

The vendor was nice enough to take the kits back, and apologetic about not suspecting this would be the case, from the new "SK" part number. He even helped out with a search for anyone still carrying the original part number (0513000-20) and KRN Aviation turned up (480-961-8946) as still having this part in stock. Two have been ordered, at $12.96 each.

If anyone knows of more economical source for these nutstrips, feel free to let us know. At least now, hopefully, anyone searching the forum on this topic in the future, can be spared some frustration.

[Watkinsnv]

Since not staying stock I changed over to seperate machine screw theaded floating nut plates and I changed over to a newer cowling. not that theres anything wrong with staying stock. Stock is good. Lance

[mit]

I put in nut plates.

[HA]

I only had a few break so I just replace the bad ones with a tinnerman clip (slides on)

A1789-8Z1D short ones, A1787-8Z1D longer reach

[davevramp]

ZetaByte

What is the "SK" part number for the replacement nut strips?
My 1954b in need of the same repair.
Thanks for the information

Dave

[blueldr]

I have found that it seems to be more practical to repair the cowling connection with individual tinnerman plate nuts. If one nut goes bad, only one plate nut need be replaced rather than the whole strip. I really think that strip was a production convenience for the manufacturer.

[mmcmillan2]

What size nut plates do we need to repair these cowl screw points?

This type?: https://www.aircraftspruce.com/catalog/ ... -8Z-1D.php

[c170b53]

Here’s where a seemingly simple thing can go so horribly wrong. Research and read the many posts on skin fuselage cracks in this area. There’s also some opinion on what the best methods are to avoid issues, Del may have the best answers. There’s a few pics in the forum on where this ends up, done wrong.

[c170b53]

I’ll show mine, I think I’ve posted this before though. Elongated holes, metal fatigue, vibration and stress. All present to initiate cracks. i

[mmcmillan2]

Can you share more details on how the cowl fasteners caused that skin to be damaged?

[c170b53]

Well, these airplanes are old but vibration, stress corrosion and wear, can make parts much older. Small cracks can become big cracks, sometimes slowly, sometimes quickly. In my case two cracks developed, one initially from a screw hole which traversed across the firewall about 3 inches. The crack then reversed course and travelled back to a rivet hole attaching the skin to the firewall, missing the closest rivet(2 rivet holes from the initial crack point). Essentially creating a large pie shape defect. I repaired that with doublers, but really the skin needed changing, the other holes were not that healthy either so I replaced it. My other side has two small cracks starting, but I’ve stop drilled those and so far, say maybe 5 annuals, no progression but I do have a skin on hand for that side.
So maybe you can do some searches here, such as forward fuselage skin, or nut plates and so forth for more info. I’ve seen other pictures such as mine, not sure whether they were on our site or others but the only difference seen is the paint schemes.