The nose gear upper housing and main gear upper housing look the same, on my fixed-gear 19/23/24. Can I make a nose housing from a main housing?
Search strings: cracked gear housing, gear housing crack, broken gear housing
These upper housings are all made from P/N 169-810011-999 origin castings. Beech assigned a P/N to each drawing, as well as to each piece of each assembly as it proceeded through machining and assembly.
The upper gear leg housing assembly, for the main legs of the fixed gear, is P/N 169-810011-25. The origin housing P/N 169-810011-3, which has a radius of .620” at the base of its column. The -3 goes to a -13, which goes to a -21, which is used in making the -25 housing assembly. The assembly consists of a -21 housing and two P/N 169-820011-11 bushings (knee pivot bushings).
The upper gear leg housing assembly, for the fixed nose gear, is 169-810000-663 (which supersedes from P/N 169-810011-27). The origin housing P/N 169-810000-7 has a radius of .250” +.000/ – .010 at the base of its column. The -7 goes to a -15 and then to a -23, which is used to make the -27 housing assembly.
The -27 assembly consists of a -23 housing and two P/N 169-810011-11 bushings (knee pivot bushings). and has been superseded to P/N 169-810000-663. However, there is a note for the -27 in the old Beech computer system which states “cannot sub for -663; needs to be reworked”. I think this rework could be installation of the main pivot bearing and its roll pins (see below).
Part number 169-810000-663 (nose gear upper housing) consists of a 169-810011-23 housing, two each P/N 169-810011-11 bushings (knee pivot bushings), one each main pivot bearing P/N 169-810016-3, and the associated three each P/N MS171528 spring (roll) pins. On the -23 housing only, the upper shaft shows a length measurement of 6.010”.
Beech would not say that any of these housing assemblies can be installed on both the nose gear and the main gear. They are all manufactured from the same -999 origin casting, but there is a difference in the column base radii. Beech could find the column height measurement only for the -23 housing; the data is unavailable for the -21 housing. Personally, I suspect that the columns are the same height, and this should be easily verifiable by measuring the column on a removed main gear upper housing. The key difference seems to be the smaller base radius used on the nose gear, to accommodate the main pivot bearing-bushing. As used on the nose gear, the column must also be drilled for the top cap fastening. Another factor in trying to use a salvaged main gear housing for a nose gear, would be the drilled column (where the through-bolt or Jo-Bolts passed through). There is no steering torque in the main gear, and the Jo-Bolts are swelled into their holes. If mounted on the nose gear, there is torque applied between the housing and top cap. The former attach holes in the center could become a focal point for stress, with resulting cracks. They would be out of sight, and the first symptom would likely be the loss of the lower gear assembly at liftoff. Particularly if someone just ignored a particularly noticeable shimmy event during the previous landing.
If anyone tries this on an official basis, it might be tough to get formal FAA approval (field approval), particularly in the absence of any support from Hawker-Beech. I would certainly suggest that any former attachment holes be carefully polished smooth. It might even be wise to fill them with structural epoxy. I have heard of this being successfully done in Australia, with a formal approval.
Keep in mind that the donut stack tube hole, where it passes through the upper housing, is not a precise fit when brand-new. The hole is more than 1/16″ larger than the tube, as it comes from Beech. This is for two reasons.
– The stack tube does not have a perfectly vertical motion that is parallel to the hole. The compressor plate is pinned to the lower fork, and the fork travels in a slight arc as the wheel goes up and down. The stack tube must be able to rock fore and aft, as it travels up and down. If the tube were to fit the hole with any type of close fit, it would bind up during some point during its travel; something would scuff or break. The fit in the hole is deliberately very loose.
– The perimeter of the donuts themselves act to guide the stack within the housing; they are a very snug fit within the housing. This will halt the oblong wear of the tube hole when it reaches about another 1/16″.
For these two reasons, I do not consider the usual oblong wear in the upper casting tube hole to be of any real significance, unless scuff marks start to show inside the housing, due to the metal washers on the donuts. If this starts to occur, you would see the debris powder at the base of the donut stack, in plenty of time to act. The stack tube isn’t intended to be a close fit. A&Ps who are accustomed to looking for looseness and wear will often condemn this part unnecessarily. It IS, however, very important to get all looseness out of the main pivot bearings, steering linkage, damper attachment, etc.