What are the options for the grease bolts used in the Sierra Main Landing Gear doors? Can I make my own as Owner Produced Parts? The Beech price for these bolts has become ridiculous.
Search strings: Sierra gear door bolts, grease bolts, special bolts, bolts with a grease fitting, gear door bushing, flanged bushing
Technical Editor:
If you make your own, take great care. I have the Beech drawing for these bolts, somewhere around here.
– The primary center hole must be quite small; 3/32” is preferred, to prevent weakening the bolt. Properly drilling the full length of the proper AN5 heat-treated bolt, while keeping the hole centered, is great sport. These bolts are made from 180,000-220,000 PSI tensile strength steel; almost the same as a Grade 8 SAE bolt (but slightly less brittle). You will need a cobalt bit, and will need to use a rigid drill press plus lubricant.
– The head end is then counter-bored just deeply enough to press in a 3/16” drive-in Zerk fitting. If you try to drill it and tap it for a standard 14-28 threaded Zerk, you’ll run the risk of the bolt head snapping off in service. Not to mention the joy of breaking off a tap in the very high-strength steel bolt.
– The threaded end of the bolt has to have a slot cut in across the base, and partially up the side, so that grease can get from the center of the bolt to the groove in the pivot pin. The bolt typically screws in beyond the location of the cross-drilled hole in the pin. If you fail to make the grease slots, grease cannot get from the end of the bolt to the cross-drilled hole (and from there to the pin groove and bushing). The result is that an attempt to force in the grease just blows the fitting back out of the bolt.
– The bolt is supposed to have a Nylock insert in the shank, to keep it from backing out, as it typically can’t be torqued down. You can get by without the Nylock, by using Permanent (red) Loc-Tite, with its matching primer. Make sure that the threads in the pin are clean, and the threads in the bolt are clean, between the head and the top of the grease slot. Apply the Loc-Tite and install the bolt, allowing it to cure overnight. Make sure that the Loc-Tite does not extend to the cross-drilled grease hole inside the pin, or you will plug up the grease passage when the Loc-Tite cures. For this reason, I avoid using Loc-Tite, nor do I use the Nylock bolt (see below).
– Because the crappy NyLock thread insert won’t really keep the bolt from backing out over time, some shops have resorted to drilling across the corner of a flat on the bolt head (there are jigs for this), drilling two holes in the door near the bolt, and safety-wiring the bolt. This is functional but unattractive; and I have seen the drillings lead to cracks in the door.
Personally, I avoid using the original spacer, washer, and grease-bolt system, anymore. I now use only the (later version) one-piece stainless-steel gear door bushing, with the integral outer flange. I use it in conjunction with the original-design (solid) AN5-6A bolt. You put the Mylar chafe washer on the spacer, and install the spacer through the door using a standard AN5 bolt of the proper length. The bolt has an MS35333-41 internally-serrated lockwasher between the head and the bushing. A trial-bolt is used to check the fore-and-aft fit of the gear door to the wing. All, some, or none of a rubber grommet can be used between the door and the gear knuckle, as needed for proper fit. If the door is too tight against the wing (quite uncommon), a standard AN5 washer can be used as a shim between the bushing and the gear pin. In some cases the bushing will need to be trimmed using a grinder or hacksaw, to pull the door closer up to the wing (it is easily cut; not a hardened steel). You have to take care with the fitting. If the bushing is made too short, the bolt will be pulled too tightly to the knuckle, with the edges bowing outward as a result. That defeats the purpose of achieving a closer fit (door to wing), and will lead to the door cracking from the bolt hole. I usually find it necessary to apply some Mylar anti-chafe tape to the knuckle, if the door needs to slightly butt against it to get the proper wing fit.
There are several significant advantages to the single-piece bushing. It is far stronger; I have never had a door bolt break, or shed a door, on a plane I’ve used this on (which is probably why Beech switched to it). Being one piece, it holds the Mylar anti-chafe washer in the proper place, protecting the door and paint. Instead of using the hollow Beech grease bolt, I use a standard AN5 bolt, also much stronger. The earlier Sierras all used a solid bolt, until Beech switched to the hollow bolt for easier re-lubrication; a step backward in this case. They did this under Beech SI-0620-204, which was an optional SI. I make a special ‘lube adapter’ for use during servicing, though the standard (original) bolt can also be used (it’ll just leak a lot during greasing). This small adapter has a Stat-o-Seal on it, to reduce leakage while in use; and it can be kept in the plane, to prevent loss. To grease the knee pin, you just remove the solid bolt and screw in the adapter until the seal hits the pin. My adapter is long enough to stick out through the door bushing. It has the Stat-O-Seal under the base nut, so it seals tightly against the pin. The base nut provides the correct spacing so that the cross-drilled hole in the pin remains unobstructed. In turn, the much more ‘open’ grease path (compared to the original slotted bolt approach), makes it a lot easier to get grease flow into the pin.
Mike Rellihan may still be able to furnish a ‘kit’ of the parts needed to convert the door attachment to the ideal method, for well under $200. They are not advertised in BAC Classifieds as they are used in the KLUX maintenance shop.