My Sierra’s Retractable Main Landing Gear (RMLG) has a very large spring on the LH and RH side. It holds the side brace over-center, to keep the extended gear locked down. These two springs have become very rusty, despite having been cleaned and repainted multiple times. What is the part number for the springs, and where can I get them? What about the hardware where the spring attaches at the lower fork boss? What is the easiest way to change them?
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Technical Editor:
The P/N for the large springs is 169-380043. In July of 2009 they were priced $550 per pair at Hawker-Beechcraft/RAPID. The Beech part is Cadmium-plated spring steel, which rusts over time due to the main gear exposure both in flight and on the ground. BAC-supporting vendor AECI makes a stainless-steel FAA-PMA replacement, which has been passivated and then re-plated with SS. The BAC member price is $200 per pair.
The following parts counts cover both main landing gear, as opposed to only one side.
The lower attach hardware seems most susceptible to corrosion and abrasion, and replacement is advised during a spring change. The required standard hardware to replace the lower attach parts is:
2ea AN44-11A, undrilled eye-bolts
2ea AN960-516L, light standard Cad-plated washers
2ea MS20364-524, shear-type (thin) Cad-plated elastic lock-nuts
Because there is no practical way to isolate the hardware from the gear fork alloy in this application, I advise against the use of stainless steel alternatives for these parts.
The upper attach tang can be cleaned and repainted while the spring is removed. The center pivot bolt with its washer and nut, which retain the upper spring attach tang, may be replaced if corrosion is evident; but they are usually OK. They are:
2ea AN7-25A, undrilled standard aircraft bolt
2ea AN960-716L, light standard Cad-plated washers
2ea MS20364-720, shear-type (thin) Cad-plated elastic lock-nuts
Again, stainless-steel is not advised in this location.
My personal preference is to use MS21045-7 all-metal, full-height lock-nuts for this location, as the shear-type elastic lock-nuts have a tendency to back off in extended service.
If you do disassemble the center pivot bolt assembly, take great care that the three bushings and two thrust washers are replaced in the correct positions in this joint; and that no pivoting parts (such as the tang or a thrust washer) are pinched between a bushing and the fastener or other part. These five items are:
4ea DU06 thrust washers, two per gear
2ea 169-810001-3 grip bushings, inside the top of the lower side braces
2ea 169-810001-15 grip bushings, inside the bottom of the upper side braces
2ea 169-810001-17 spacers, inside the grip bushings
By far, the easiest way to replace the spring is to remove the top stack tube nut while the plane is on the ground. Then jack the plane, using the under-wing jack pad, and allow the wheel to roll forward while the stack tube clears the upper housing and swings clear. If new donuts are being installed, and are frozen while awaiting use, the spring and lower eye-bolt can be changed without any big rush. If the original donuts will remain in place, you must work very quickly to change out the hardware, get the stack tube back in position, and get the plane’s weight back on the gear. This must be done before the donuts swell out so far that the washers and nut cannot be reinstalled, or the nut cannot be adequately adjusted (for the proper donut stack height), without the use of excessive force. If the nut cannot be reinstalled, the donuts will have to be removed, re-heated, re-compressed, and re-frozen, before another attempt is made to reconnect the stack tube. For this reason, if the donuts are new, or there is not yet about a quarter-inch of clearance between the nut and top washer from normal ‘set’ (with the plane on the ground), donut compression equipment should be on hand.