I noticed a spot on the RH side of the round ring or collar at the top of my Sundowner’s landing gear. It looks like a big countersunk hole, but either with nothing in it, or with something blocking the bottom of the hole. My mechanic thinks it’s supposed to be that way, because he can’t find anything about it in the parts manual. All he can find refers to some small roll pins in the big bearings. Do I need to worry about this?
Search strings: Nose landing gear, nose gear repair, countersunk bolt, big screw, big countersunk screw, large screw, large countersunk screw.
Technical Editor:
There is indeed supposed to be a flat-head bolt in that big countersunk hole. It is called a ‘bolt’ because of its size; but it is actually a large 5/16” flat-head screw that requires a #3 Phillips screwdriver. You should not operate the plane with the bolt broken, for several reasons. One is that you are at risk for the broken end falling down into the donut stack inside the tube, with the result being badly damaged donuts, damaged housing, or both. Either of which would be very expensive. Another is that this bolt is an important piece to prevent or control a bad shimmy event. This ‘third bolt’ in the top collar keeps the collar from ‘cocking’ toward the two centering cable bolts, thereby adding as much as .020” clearance to the bearing’s shim height. That is far too much vertical clearance, making the gear much more prone to shimmy.
Technicians are sometimes confused about this bolt. The early 1962-1963 planes indeed did not have this third fastener. The bad in-service experience with the nose gear developing excessive play (in part during the Flight Of The Three Musketeers in 1962) led Beech to add the third countersunk ‘bolt’ in 1964. They made well over 200 changes like this between 1963 and 1964, with many more coming later. A great many hardware changes were never reflected in the IPC, the Shop Manual, nor in bulletins. To illustrate, the collar part number is 169-810000-49; it has had that same part number since it was first published in in an IPC in 1962. Despite having the same P/N, the collar began life with 2ea 5/16” holes (centering cable only); then went to 3ea 5/16” holes (two centering cable bolts plus new AN509 bolt); and then while still having three holes, the two centering cable bolt holes were changed to size 3/8”. That’s what you will get if you order a new collar today. When someone goes to put it on an earlier airframe , they discover that theirs does not have the third hole (1962-1963); or that they do have that hole, but their centering cable bolts are too small for the new collar (1962 through early 1968, 5/16” rather than the now-required 3/8” bolts, as illustrated in SI-0117-207). As with so many other parts, Beech never changed the IPC illustrations to show the third bolt; not even for the Sierra. The Sierra drawing does not show ANY of the three bolts; neither the countersunk bolt nor the two hex-head bolts that are used in lieu of the centering cable placement on the fixed-gear planes. Added misdirection can come from the three spring pins originally used to retain the big bronze pivot bearings. But the big flat-head side bolt has nothing to do with the bearing pins.
Your technician can identify the original hardware in IPC 169-590012-J2, figure 206, page 4. It is listed just below key number 33 (nose wheel steering collar), in the list of attaching parts. It is shown there as P/N AN509-516-17, which has been superseded by P/N MS24694S147.
What I recommend, however, is bolt P/N NAS1205-7. This is a very high-strength bolt that has a closer-tolerance fit. It helps to remove any slight play caused by wear in the holes of the collar and the column. The standard AN509 bolt is 125 KPSI tensile strength; the NAS1205-7 has a rating of 160-180 KPSI; almost 30% stronger. The NAS bolt is used with an AN960-5L (light 5/16”) washer and an MS21042L5 all-metal reduced-diameter magnafluxed lock-nut. It holds much better than the original AN365-5 elastic lock-nut, and is designed to work with the shorter threads on the NAS1205 bolt.
Replacing the bolt will require removing the top steering adapter, to access the inner nut. You do not have to remove the two AN6 centering cable bolts; though if they are frayed this would be the time to change them. There is also supposed to be an AN960PD6 washer on the CC bolts, between the cable and the collar. This is what clamps the cable without having to over-tighten the bolts. If the PD washers are missing, your cable will already likely be cut. In that case, it should be replaced. This is also a good time to check the nose gear centering spring for rust. They are inexpensive; and far less expensive than what happens of the spring breaks and the nose wheel comes down while canted sideways from a cross-wind landing. The eyelets on the ends of the steering cable must be safety-wired together, as well as to the spring loop. Otherwise one is guaranteed to pop off during taxi (or even in flight, during strong rudder work).
The six cap adapter bolts are 10-24 drilled-head bolts, not the more common 10-32 size. Because of the deeper threads, they are relatively weak, and must not be over-tightened when reinstalled. They only require about 20 INCH-pounds (not foot-pounds). They are safety-wired, and do not rely on torque to remain in place. Make sure they can be freely inserted in their adapter holes; and make sure they have an AN960-3 flat washer, NOT a lockwasher of any kind. Each one must be carefully inspected when removed, for any sign of ‘necking’ or twisting. If a damaged bolt is reinstalled, it will almost certainly break off in the alloy collar while being snugged down; a new collar runs around $500. Broken bolts can seldom be removed, because of the softer alloy surrounding the bolt fragment. Prevention is everything.
When the three collar bolts are reinstalled, the nose gear must be aligned straight with the plane, NOT with the spinner (which will be offset). Only then can the centering cable bolts be snugged down. They do NOT get torqued to normal values; just tightly enough to clamp the cable. If you put an open-end wrench on the head of each bolt, you should be able to rock the bolt back and forth without any great force. Ditto on the big screw; you should still be able to rotate it slightly using the big #3 screwdriver.