Q&A: Engine cowling mounting and support system upgrades, and a solution for chronic elevator and rudder bearing replacement

Written by Steve Ells
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Steve, 
This year I took my 1976 Cessna 182P to a new shop for my annual since I heard that it a good idea to switch to a different shop from time to time. The new shop manager called me to say that the airplane was in pretty good shape, but... (hearing "but" from a new mechanic is never welcome!).
Most of the squawks he read off over the phone were not unexpected, but one was. He told me that the cowling shock mounts were completely worn out and that had allowed the cowling to move so much that the center induction tube and the carburetor inlet duct had been worn through.
Needless to say, this is a complete surprise to me. I went down and took a look, and he's right. It looks like the wear has been going on for some time.
Have you seen this before? Is it unusual? Is there anything that can be done to eliminate this kind of wear?

—Bad Cowl Carl

 

Dear Carl,
I have seen this kind of wear before, although mechanics usually catch it before it gets as bad as yours. The photo (page 23) details a repair of another seriously damaged cowling.
Cessna changed the engine cowling mounting and support system beginning in 1973 with serial number 61426. Prior to that, the upper and lower cowling assemblies were secured to the forward portion of the fuselage with either screws (in earlier 182s) or quarter-turn fasteners.
The 1973 cowling mounting change consisted of attaching the upper and lower cowling halves to 12 rubber-mounted quarter-turn receptacles located around the perimeter of the firewall. This change was designed to completely isolate the cowling assembly from the airframe. It was supposed to reduce vibration and noise.
The change also included a sheet metal support assembly and shock mount that was installed above and across the forward end of the inlet air duct in the lower cowling. This shock mount acted as a rubber bumper that was designed to rub against the balance tube that connected the forward ends of the left and right manifold tubes of the engine induction system.
The new system worked, but it did introduce another maintenance task: making sure the rubber mounts of the receptacles (part number S2155-1, shock mount) were airworthy.
It's very easy to visually inspect the system. During the preflight walkaround, check to see that the gap between the forward end of the fuselage sheet metal and the aft end of the cowling assembly is even all the way around. The cowling shouldn't touch the fuselage.
In my opinion, this system was poorly designed. The shock mounts are not stout enough and the studs and retaining rings (part numbers 27S 3-2 and 27S 3-3; 2600SW2) were also too small.
The normal system failure pattern starts when the rubbers of the lower shock mounts soften due to exposure to engine oil and heat. This failure allows the cowl to sag and the other rubber mounts are conscripted to take up more load than they were designed to handle. This further contributes to the sagging.
As designed, the shaft of the studs should be aligned perpendicular to the receptacles in the shock mounts, and will work—when the cowling support system is in good shape. However, after sagging starts, the weight of the cowling assembly creates higher-than-designed loads that quickly cause accelerated wear in stud mounting holes in the aluminum cowling.
In a worst-case scenario like yours, it's almost certain that you will find elongated stud holes in the upper and lower cowling.
Cessna continued to use a similar system in spite of these problems. In 2008 Cessna Service Bulletin 08-53-01 was issued to combat firewall cracking in new 172s. The provisions include "a more detailed inspection of the engine cowling installation for alignment, fit, and clearance with the fuselage; and for cracks in the firewall. [As well as] to provide modifications for the cowling shock mount attach brackets and engine baffle seals."
In the case of your aircraft, your mechanic will need to determine if the wear in the induction inlet duct in the lower cowling requires the installation of a patch; will need to inspect the induction crossover tube and repair (or replace) as necessary; remove and replace the support assembly (part number 0752058-1, cost is around $500); and repair and/or upgrade the cowling support system.
To the best of my knowledge there are two companies that offer upgrades of the cowling support system. A kit from MilSpec Products includes improved fasteners and other parts. Kit MSC182-40P fits your airplane; list cost is $483.62. I haven't installed one of these upgrades.
The kit that I have installed is from Skybolt. This top-quality kit takes care of oversized holes and provides a permanent solution to shock-mounted cowling woes. The Skybolt kit for your 182 is SK203C182P4; list price is $696.61.

Happy flying.
Hey Steve,
I fly a 1970 Cessna 185 on Edo 2960 floats during the summer. (I put the skis on in the winter.) It's a great airplane and has contributed immeasurably to my enjoyment of life in the outdoors over the years.
This year during the annual, my mechanic again wants to replace the bearings in the elevators and the lower bearing in the rudder. I never dip into any saltwater, but I'd say I end up replacing these bearing every few years—and I must not be the only one that's buying new sets of bearings on a regular basis.
These little things cost about $80 apiece and I'm hoping there's a better product out there. Can you help me?

—Rusty Bearing

Dear Rusty,
I was lucky enough to spend some time riding around in a C-185 on 2960s during herring-spotting season in Alaska. It's a very good airplane/float combination. Since I also did the maintenance on it, I'm well aware of the cost of changing those bearings.
The bearings are part number MS24462-4 and the best price I could find was $60 each from Skygeek. If all eight need replacing, you're looking at some change—and there's no guarantee you won't have to replace them again soon.
Fortunately for the owners of Cessna 180s, 185s, 206s and 207s, Cessna Flyer Association supporter P. Ponk Aviation in Washington has a bearing that's approved by PMA to replace the steel needle-type bearings that are original equipment.
The P. Ponk bearing replacement is manufactured of an advanced polymer, is corrosion resistant, self-lubricating and requires very little maintenance. When I talked to Steve Knopp, the owner of P. Ponk Aviation, he told me that a customer flying a floatplane in saltwater in Juneau, Alaska has had a set of his bearings for eight years and has had no problems.
The P. Ponk polymer replacement bearings retail for $69.95 each. If four or more are ordered, the price drops to $65 each. I believe your rudder and elevator bearing problems may be over.

Happy flying.

Know your FAR/AIM and check with your mechanic before starting any work.

Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He's a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to .

Resources
Cessna Service Bulletin 08-53-01
"Engine Cowling Alignment Inspection and Modification"
CessnaFlyer.org/SB08-53-01

Cowling fastener kits
MilSpec Products, Inc.
milspecproducts.com/product/conversion-kits-cessna

Skybolt
skybolt.com
OEM steel needle-type elevator and rudder bearings
Skygeek
skygeek.com

Low maintenance polymer replacement bearings
P. Ponk Aviation
pponk.com

 

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