Bellanca Cruisemaster
Landing Gear Bolts
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The Cruisemaster landing gear is a relatively simple oleo strut, where the lower moving portion of the strut is retained and oriented by a "nutcracker" scissors link.  The fit of the bolts in this scissors link determines whether or not the wheel will track straight.  At my first annual I was horrified to discover that '77B's gear could track plus or minus about 7 degrees from centerline due to sloppiness in the scissors linkage.

This was due to two things that would be a good idea to check on all Cruisemasters:

  1. The bushings in the scissors linkages were worn, which is normal wear and tear.
  2. The bolts were too short, so that one side of the linkage was riding on the bolt threads instead of the shank.  Since the threads are smaller than the shank, and additionally the threads will cut into bushings, this was probably the cause of the looseness.

The fix involved rebushing the linkages, which is easy, and replacing the bolts, which turned out to be a bit of challenge.  The reason is that the original bolts were standard AN bolts which were sized based on overall length to not protrude far out from the scissors linkage due to interference with the rest of the landing gear mechanism when the gear is retracted.  AN bolts have a relatively long threaded portion relative to the shank portion of the bolt, and the size of the threaded portion of not constant but changes proportionally to the overall bolt length.  This means that an AN bolt properly sized for the landing gear bushings based on grip length (or the length of the shank) would have been too long in the thread area, necessitating a big stack of washers.

The solution is to use NAS bolts, which have a threaded portion of constant length regardless of the shank length.  NAS bolts also have an additional benefit in that they're close-tolerance bolts for a tighter, more consistent fit, and they're high-strength.

Landing gear bolt comparison photo

From left to right, this photo shows the difference between a new standard AN bolt of the nearest correct shank length for the application, a new NAS bolt of the correct shank length, and the originally installed AN bolt with the too-short shank.  Notice the length of the NAS bolt and the originally installed AN bolt almost exactly match, but that the shank on the NAS bolt is longer.  This is good because also notice the wear on the upper portion of the threads of the originally installed AN bolt.  This wear is due to the threads riding directly on the landing gear bushings.

The disadvantage of NAS bolts is that they're expensive and hard to find, especially in the 6 and 7 sizes needed by the landing gear.  I eventually found some from California Aerospace Fasteners in San Diego, California.  Once you get the bolts you then you have to find a machinist to drill out the center of the bolts in order to install a grease zerk to grease within the scissors link bushings.  Be prepared for complaints because the bolt material is extremely hard and difficult to drill out.

Note:  In 1998 a Viking was damaged on landing because the bolt cracked and broke in half where the grease hole was drilled.  The bolt pieces departed the airplane and the wheel swiveled off centerline, with a predictable ground loop and spar damage from the landing gear housing overstressing the spar attachment points.

It might not be worth having the internal grease hole, instead keeping the bolt undrilled for full strength and simply manually removing and re-greasing the bolt at every annual.