Belleville Spring installation

by Bill Bayne

Univair's Service Kit SK-35 and Skyport Modification Kit SMK 115 retrofit Ercoupes from Serial No. 813 up and early Forney F-1s with Belleville Springs (replacing the original solid rubber "donut" taxiing shock absorbers).

I believe this is the text from the instructions you want (it's just a typed logo or letterhead):


M. D. Hubbard Spring Co.
217 Central Ave.
Pontiac, Michigan

(as furnished by Forney as FMK-9)
Eligible for installation on Aircraft Certificated under under Type Certificates 718 (Models 415C & CD) and 787 (Models 415D, E, G, F1 and F1A). (Serial 813 and higher)


After removing the Shock Strut Cylinder from the ship, remove with a pair of crew drivers, the retaining ring. After removing the pressure cap, remove the Rubber Buns and Aluminum cups. After lightly coating the cylinder on the outside with grease, install 7 Belleville Clusters in place of the Rubbers and Cups. Replace the pressure cap and retaining ring after shimming the bottom platform to the correct height. The top pressure cap should be snug against the retaining ring, but should give only light, or no pressure on it. With the ring replaced, the shock is reasy to reiinstall in the ship, using the new "O" ring (part 6227-17) on the piston and the proper oil iin the cylinder.

Oleos in Ercoupes (et al) Serial No. 813 up were manufactured for sealing with an AN6227-17 O-ring and were filled with red hydraulic oil.

Since the oleos tend to wear fore-aft only, the cylinder elongates over time to become sufficiently oval that an O-ring can no longer seal properly. Skyport has long offered an STC-FAA-PMA Kit, SMK 61 to install the earlier cup seal as an alternative to the original O-ring. With this kit installed, the oleo must be filled with automobile brake fluid.

Whichever is fitted, it is recommended that the seal be replaced whenever the oleo is disassembled.