Q: Hi Steve,
I own a 1975 Cessna 172 M and this cowling is in bad shape. The little fasteners don’t grab very well and as a result, the holes in cowling are getting bigger and bigger. I’ve looked at other 172s on the airport with this same cowling setup and I’ve seen some that have “solved” this problem by putting a big washer under the fastener.
I think that looks tacky. Isn’t there a better way to resolve this?
A: Dear Sloppy,
Yes, there is. The mounting system of the cowling on your 1975 M is designed to isolate it from the vibrations produced by the engine and by the airframe. The components of this isolation system are 11 shock mounts. The base of each mount is secured to the fuselage structure by two screws. The receptacle for each cowling quarter-turn fastener is molded into a rubber donut which is bonded to the mounting base. Shims can be installed under the mounts to “center” the cowling assembly and prevent cowling-to-airframe and/or cowling-to-engine contact.
There is also a mount located at the front end of the lower cowl half. This mount is often the same part number as the shock mount mentioned above, but it is called a snubber and it is supposed to prevent the cowling from being displaced due to aerodynamic forces during cruise flight.
Cessna issued a great deal of service information related to this cowling. SE78-15 and SK172-48A directed owners to replace the aluminum snubber bracketry with a steel bracket; this bulletin also directed owners to change the number of washers under the upper and lower engine mount bolts. Additionally, SE78-15, SE74-27R1 and SE86-076 attempt to provide a solution for extending the life of lower cowl-mounted landing/taxi lights since the vibration-isolating cowling design scheme didn’t stand up to normal use.
Sagging mounts, mounts that de-bonded from their mounting plates, the costs of replacing new parts and too little bearing surface on the small quarter-turn Southco fasteners resulted in accelerated wear in the aluminum cowlings. As a result, Cessna issued SEB86-06 and Service Kit 172-90 in 1986. This bulletin provided a cowling fastener improvement kit and applied to all Cessna 172s from 1968 to 1985, and 1983 and 1984 Cutlass aircraft.
The kit provides parts and instructions for replacing the original equipment Southco fasteners with Camloc fasteners and receptacles. The service kit is still available from Cessna. List price is $2,690.
Skybolt Aerospace Fasteners of Leesburg, Fla. sells an STC approved fastener replacement kit. The kit includes Camloc fasteners, Camloc receptacles, and a locator template; adjustment washers that Skybolt claims will easily solve cowling adjustment problems; and a pair of Camloc pliers. Cost for
the Skybolt kit is $688.
Skybolt also sells a complete line of OEM (Southco) cowling hardware.
I’ve installed a Skybolt cowling fastener upgrade kit and I thought it was a super upgrade. According to Skybolt, the kits have been improved twice since I last put one in.
Q: Hi Steve,
I recently bought a real nice 1966 Cessna 310K. I’ve always loved the way 310s look fast even when they’re sitting on the ramp. This one seems to be a very well maintained and cared for airplane.
In spite of getting what I thought was a thorough pre-buy inspection by a guy who I was told knew 310 systems and engines inside and out, a problem has come up during my annual. I have no doubts that the airplane is sound mechanically; unfortunately, the pre-buy guy wasn’t all that sharp on paperwork and records.
Now the mechanic at my home field has run his fine-toothed comb through the aircraft records and has asked me where the paperwork is for the alternators, since the 310K was originally equipped with generators.
I’ve looked everywhere and don’t have any more paper related to this airplane. He won’t sign off my annual until I get the appropriate paperwork. What do I do??
A: Dear Stuck,
There’s an old joke in the aero maintenance business that says the annual isn’t complete until the weight of the paperwork equals the weight of the airplane. Sounds like it’s true in this case.
The 1966 310 K was the last year that came out of the factory with generators instead of alternators. I spoke with Tony Saxton at TAS Aviation in Defiance, Ohio—he is a 310 expert—and Saxton said that Cessna never offered a service kit to upgrade your 310 from generators to
Based on my research on the FAA’s STC listings pages, two companies hold STCs for the installation of alternators on a 310 K.
The first is Plane Power out of Granbury, Texas. According to the person I spoke with there, all you need to do to get the STC paperwork is hit the “STC Approval Request” tab on the Plane Power website. (See Resources at the end of this column. —Ed.) It asks that you download a form, fill in some blanks on the form and send it back electronically, by fax or by snail mail. You can get a good look at the Plane Power alternators at the website, too.
The second company that sells STC approved generator replacement alternator upgrade kits is National AirParts of Deland, Fla. Its alternator, the N300, produces 70 amps.
If there’s no evidence (such as a data plate) that the alternators installed are from either of these two companies, there’s a possibility that an owner purchased the alternators, bracketry and related accessories for an alternator installation off a (wrecked?) later model Cessna 310 and installed the alternator system under a one-time field approval. Since an FAA maintenance inspector would have signed off the approval, there’s a real good chance that paperwork is in the FAA records office.
The first place to start your search for paperwork to support the alternator installation would be the FAA aircraft registry office. All FAA form 337 submissions (forms sent to the FAA detailing each major repair and alteration) on your aircraft N-number are on file in the registry office. Go to the registry website and click on the “Request for Aircraft Records” link (just above “Help” on the left margin). After you pay $10, the records will be copied onto a CD and the good folks at the records office will send it out. As I recall, the CD arrives pretty quickly.
If the records search doesn’t show the appropriate 337, then I would post a request for a copy of a field-approved 337 for the upgrade to alternators in place of the original generators on a 310 on Cessna Flyer Association’s member forums.
Your mechanic would then submit that 337 copy with a 337 detailing the installation on your airplane to the local FAA maintenance inspector, and ask for a field approval. A previously-approved 337 is often considered to be acceptable data for the field approval.
If none of these avenues yields results, you have two choices. You and your mechanic can petition the primary maintenance inspector (PMI) that covers your area for a field approval of the alternator installation. Your airplane is grounded until you obtain the field approval.
This process will take time. Here’s why. Each PMI may approve or disapprove field approvals as he or she sees fit. By granting a field approval, the PMI takes responsibility for the approval of the modification. Some PMIs shy away from signing field approvals; others are more accommodating.
The second option, although expensive, may be less cumbersome than the field approval process. Simply purchase a pair of STC’d alternators from either Plane Power or National AirParts, install them in accordance with the STC instructions, and get back in the air.
Steve Ells has been an A&P/IA for 38 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 (www.EllsAviation.com) and lives in Paso Robles, Calif. with his wife Audrey. Send questions or comments to .
Know your FAR/AIM and check with your mechanic before starting any work.
310 Information and Repair
TAS Aviation, Inc.
Cessna Flyer Association’s Online Forums
Plane Power, Ltd.
National AirParts, Inc.
Form 337 Searches
Cowling Fastener Upgrade Kit
Skybolt Aeromotive Corp.
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