Lead Counterweights on B-models

How to keep the Cessna 170 flying and airworthy.

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GAHorn
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Joined: Fri Apr 12, 2002 8:45 pm

Lead Counterweights on B-models

Post by GAHorn »

Cleo Bickford is even pickier than I am! (If you can believe that!) He pointed out that the counterweights on my 170-B model is the only one he's ever seen that are attached like the Illustrated Parts Catalog shows. The Parts Catalog shows the lead weight attached with 4 rivets. (B-models only,...the 170 and 170A do not have counterweights.) The interesting thing about that is,...How do you fasten those rivets? Since you can't "buck" them in the traditional sense because they are embedded in solid lead, ...how are they fastened?
The Parts Catalog list them as two each NAS445-163C-4-2, and NAS445-163C-4-8 rivets. I've not found a hardware listing/description of those type rivets, but looking at my airplane, if that's what these are, they are very similar to "Cherry-Max" rivets, and appear to be self-expanding.
(That's what it appears on my airplane anyway.)
Looking at other airplanes on the ramp, if you allow the elevator to fall completely into the nose-down position the counterweight can be viewed. Look at the inside edge (vertical surface) of the counterweight area, alongside that full-length rib of the counterweight horn. You may find two screws, either MS or PK style, that screw into the lead weight to hold it in position. At least that's the way it's been described to me, and that's how other airplanes are typically found. The Parts Catalog do not show these. I suspect they've been added either by subsequent Service Letter, or by well-intentioned mechanics. Either way, I think there's a danger here.
DURING PREFLIGHT INSPECTIONS, be absolutely CERTAIN that those screws, if installed, are in-place and FULLY screwed in. (Don't strip them out in that soft lead or they'll work themselves out.) If those screws are there, and if they back out of that lead, not only can the lead become dislodged and send your elevator counterweight data into never-never-land,...but the screws could interfere with the horizontal stabilizer and LOCK YOUR ELEVATOR UP IN FLIGHT!!
hallwerks
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Joined: Mon Apr 22, 2002 5:05 pm

170 B elevator counter weights

Post by hallwerks »

An owner reported that during pre flight he noticed a loose rivet. picking at with his finger tip , the head popped off he then found several more. All that had been holding them in was the paint. These are 1/8" universal Cherry Max rivets with an al rivet and al stem. Tom
Tom Hall
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GAHorn
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counterweight rivets

Post by GAHorn »

A BIG THANKS to Jimmie L. Mathis up at Boeing for three days spent researching this question. Cessna's IPC listed the parts as:
NAS445-163C-4-2 (2 ea) and NAS445-163C-4-8 (4 ea). Further to the right, on the same line, they offer in parenthesis (CR163C-4-2, and CR163C-4-8 ).
Jimmie pointed out that NAS445 specification is not a rivet at all, it's a nutplate, tinnerman-style.
He researched some more on rivets and here's what he found.
==============
The Cherry Rivet was approved to the BACR15E specification (Boeing Airplane Company).

Material:
Rivet: 2117-T4
Stem: 2017-T4
Finish anodize Rivet and Stem
Alumilite 205 Yellow Rivet and Stem

Note: 163C was colored. 163 was not colored.

Cessna blew it on the NAS445.
TEXTRON AEROSPACE FASTENERS (CAGE CODE 11815)(formally Cherry)

Boeing
RIVET, BLIND, UNIVERSAL HEAD (SELF-PLUGGING)
CR163C-4-2 ==>BACR15E163C4-2 ==> BACR15E-163C-4-2 ==>
NAS1398D4-1 ==> NAS1398D4A1

Douglas
It showed CR163-4-2 (NO C) == > MS20600AD4-2
(Canceled May 2000, goes to NASM20600)
==============

So it looks like the rivets are really just CherryMax type rivets, aluminum. The above part numbers (not the NAS445 numbers) should assist anyone looking for the correct parts.
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