With the coming of spring and many members contemplating changing the shock cushions (aka ‘donuts’) on their planes, here is an excellent article written by the GREAT ONE, Mike Rellihan. The article has lots of helpful information. Read and learn!Please note, the Beech Aero Club mail address changes over time as it is always maintained by the current treasurer. Please send any payments to the current club address at https://www.beechaeroclub.org/content.php/64-Club-Contact-Info.
I need to install new gear cushions (new donuts). What can you tell me about BAC tool rental? Jo-Bolt tools? Jigs or fixtures used to pre-compress the new cushions? Landing gear play? Landing gear repair? (Search strings: gear cushion replacement, donut replacement, tool rental program)
The BAC tool rental program is ever evolving. Here is the current status: Consistent with the Bylaws, the Beech Aero Club has invested membership money to purchase specialty tools for the utilization of active members on their personal aircraft. The purchase price of these tools, and the infrequent requirement for use, make it impractical for the individual owner to justify their purchase.
The tools are not available to non-members or for commercial purposes.
An active member may allow the tool(s) to be used by their A&P mechanic for repairs to the member’s aircraft. The tool(s) are also available directly to A&P mechanics for use on a member’s aircraft. If the aircraft owner is not currently an active member, the club membership must be paid prior to shipping the tool.
These tools are made available at nominal charges to, or on behalf of, active members. The charges are to cover the cost of repair and depreciation of the tool(s). The tools and charges are enumerated below.
The active member or their A&P shall provide an aircraft N-Number along with the request for the use of the tool(s). Prior to shipment, the charges for the use of the tool and the out-bound shipping must be paid. The active member using the tool(s) shall have use for thirty (30) days and shall return the tool(s) timely for use by other active members. If the active member has a delay in repairs and use of the tool(s), that active member shall, before expiration of his thirty (30) days of use, request an additional thirty (30) days.
These tools are positioned in various regional locations to help keep the cost of shipping as low as possible. The member is responsible for return shipping on the tool(s). In the event that another member has reserved the tool for subsequent use, the tool may be shipped directly to that member. It is then their responsibility for shipping back to the tool holder. Shipper will insure the tools for a value of $900.
Members are encouraged to schedule the tools and necessary work to minimize the holding time on the tool(s).
Tools Member Rate
Pneumatic Jo-Bolt Tool Kit* $30.00 + shipping
Donut Freeze Comp $30.00 + shipping
Donut No Freeze Comp $30.00 + shipping
Jack Pads $30.00 + shipping
Sierra MLG Comp $30.00 + shipping
If a member/shipper does not insure the tools and if tools are lost or not returned, the member/shipper will be responsible for the tools value to be paid to the Club as follows:
Pneumatic Tool – $2500.00
Fixed gear donut compression tool – $100.00
Retract gear donut compression tool – $300.00
Jack Pads – $150.00
Pneumatic Tool tip adapter – $15.00
*A Kit includes the pneumatic tool, jack pads and donut compression tool. Rental is $30 plus shipping to member and return shipping to tool holder per kit, each kit will consist of a combination of freeze or no freeze compression fixtures, jack pads, and pneumatic JO Bolt tool or tool tip depending upon aircraft model and the methodology the A&P intends to employ.
– We currently have three sets of tooling for pre-compression of the fixed-gear or retract gear donuts. There is a different set for each type; shipping costs are currently $30.00 plus insurance with replacement of any lower for the fixed-gear set, as it is several pounds lighter. The retract set has thicker end-plates, and is designed to compress the eight heavier donuts used on the Sierras for the main gear. You to keep the compressed set for the second main gear frozen, while you work on the first main gear leg. The nose gear set, and the main gear sets for the fixed-gear planes, also get pre-compressed as complete sets of eight donuts.*Kit includes pneumatic tool, jack pads and donut compression tool. Rental is $30 plus shipping to member and return shipping to tool holder per kit, each kit will consist of a combination of freeze or no freeze compression fixtures, jack pads, and pneumatic JO Bolt tool or tool tip depending upon aircraft model and the methodology the A&P intends to employ.
– We have a professional pneumatic Jo-Bolt setting tool, if you have compressed air available.
– We have a hand tool for setting Jo-Bolts. It costs less to rent and ship. It is a bit harder to get a tight set on the Jo-Bolts with this tool, especially if the bolt hole has been slightly worn due to loose fasteners. This tool has been successfully used for may years by many mechanics, and is capable of producing good work when properly used. Unfortunately, the success rate for a good Jo-Bolt ‘set’ is much lower with the hand tool than with the air tool.
– We have a Stabilator rigging tool (Travel Board). This is a rare tool, somewhat bulky to ship, but indispensable when needed.
The intent is for the rental to include outbound shipping, plus a small contribution to help pay for the tool or fixtures, over time. The renter will be responsible for return shipping costs, as well as for the initial rental fee and deposit, if a deposit proves necessary. Some of these tools cost a great deal of money (for example, more than $700 for the pneumatic Jo-Bolt tool).
I am expecting a protocol to be defined by the BAC Board, to help keep track of the tools. For example, a renter might be required to send a status note each Monday and Thursday, until the tool has been received back at its storage location. Volunteers (as usual for all BAC roles) will be handling the tool rental; we don’t want them to have to create a lot of follow-up notes to keep track of things.
Thomas Morgera – firstname.lastname@example.org manages the tool sets in the USA. There is one tool set that Bruce Byer – email@example.com manages in Canada. There is also one tool set that Jerry Neild – firstname.lastname@example.org manages in the UK for our European members. The fixed-gear fixture kit includes the Jo-Bolt pneumatic tool, and three donut compression fixtures. The Retract kit includes a nose gear compression fixture and two main gear compression fixtures, plus a wrench for the MLG stack tube nut.
Keep track of the thin steel or 5/16″ aluminum spacer plate at the bottom of the stack tube, next to the compressor plate. It often sticks to the bottom donut, and it falls off the tube very easily. It must be located at the bottom of the stack, under the donut set (on all three gear). If a gear leg has only the thin spacer, only the 500×5 tire (Sierra nose) or 15x600x6 tire (fixed-gear nose and mains) may be used. DO NOT install a standard 17.5x600x6 tire on a gear leg unless it has the much thicker 5/16″ aluminum spacer under the donuts. Otherwise you are at risk for damage to the underside of the upper housing, and you could experience a tire blow-out during a hard landing.
When you are ready to compress, make sure that the donuts feel almost hot to the touch (but not hot enough to burn you). Long slow heating will ensure heating throughout the rubber. Coat the donuts and spacers with silicone grease (not a solvent-based silicone spray); Dow Corning DC4, as used on oil filter gaskets, is fine. Put the compression plates and washers over the donuts, and apply anti-seize compound to both the threads and the contact area where the nut rubs on the big washer. Then run the nut down. The nuts and washers are both Grade 8 steel, to resist scuffing and galling.
Put the double-nut ‘holding end’ of the fixture in a good vise, and crank the handle down tight. I also use a big C-clamp on the working end steel plate, to keep it from rotating with the nut, but that’s not critical.
Using a long 15/16” wrench (1 and 1/8″ on the Sierra MLG compressors), run the nut down until the end plate hits the spacer tube inside. You should feel the sudden difference in force to turn the nut. When the nut stops, the plates should be pretty close to 6” apart.
– DO NOT use an impact gun (air or electric) to run down the nuts! This will ruin or break the threaded rod, and you may find yourself with a set of donuts locked on the rod with a semi-welded nut.
– Before installing new donuts, be sure to carry out the compressor plate/stack tube retaining pin (roll pin) inspection. Select the correct size of drill bit (as outlined in the CMM, for mains and nose), and make sure that it passes freely through the roll pins. If the roll pins have been deformed and the drill bit won’t pass through, this is an indication of either a hard landing, or of someone cranking down too hard on the donut stack tube nut in the past.
Please return the fixtures as soon as you can, either to the coordinator or to the next waiting member. It should cost you about $25 to ship them back, if you are using a UPS or FedEx Ground shipping account. The walk-in price is probably a bit higher. FedEx Ground is probably a bit less, if it is nearby. The US Postal Service will charge you a fortune for something this heavy. Please purchase adequate insurance on each shipment; $200 on the retract set, $900 for the fixed-gear set with the pneumatic Jo-Bolt tool included.
Working on the gear itself, aside from a simple donut change, is a much more elaborate undertaking. If you do not have experienced help, one option is to ship it to me for bushing repair and donut installation (nose gears, and fixed main gear legs). I can also provide bead-blasting, chromic acid re-treating, and professional powder coating (usually in white; limited other colors may be available). Current Hawker-Beech primary gear parts (and others) come radiant-cured powder-coated from their vendors, per our tour guide in the Wichita plant.
– Play at the bottom of the wheel (in any direction) will likely be 1/16” to 1/8”, when everything is near-new. I consider any play exceeding about a quarter of an inch, in any direction, to warrant repairs as needed (tighter wheel bearings, knee bushings, pivot bearing re-shimming, main gear bracket and attach bolts). The sooner you address excessive play, the less shimmy exposure you will have, and the less the likelihood of needing major parts replacement.
– The upper thick rubber abrasion washer is often missing (from the tube above the casting, below the washer and nut). Sometimes incorrect (or missing) top washers are found; and the elastic thin ‘stop’ type nut often needs replacement. It will only be holding with about one thread showing above the nut; so it should be replaced if it does not seem to hold good friction.
– The knee pins and compressor plate pins should have grease passages and grease distribution grooves, regardless of whether they also have grease fittings. Early production parts did not; most production from the mid 60’s onward have proper machining. Replacement parts are a crap-shoot; you never know what you’ll find wrong with them. I have actually received new knee pins with grease fitting, which had no drillings for the grease to get to the bushings. A flush Alemite gun needle does not really require an actual fitting; but the fitting will keep dirt out of the grease passage. A 1/8” hole with a smoothly chamfered opening will seal the grease needle just fine. Many original Zerk grease fittings do not have check valves in the fitting; but all of the Alemite flush fittings have a flat check valve plate in them.
– Years of low usage and poor greasing will probably show up as ‘dry fittings’. The only sure-cure is removal of the knee and compressor plate pins, thorough cleaning, and a good polishing (after any needed machining to add missing grooves or grease passages). Note that the grooves and drillings only serve the end they are on; the center grease boring does not pass from end to end, or grease will escape through the retaining pin bore. Dry fittings are most often the result of the Mil-Spec grease ‘bleeding out’. The oil drains out of the clay carrier, leaving a joint packed with dried bentonite (clay; so-called ‘microgel’). If you are using the book-specified grease, as opposed to a much more modern synthetic lube with a synthetic carrier, I highly recommend re-greasing at least every six months. Each greasing should move enough lube to flush out all of the old carrier; not just until grease movement is seen in the joint. The only proper grease is Lithium-based; and example is Aeroshell #33.
– Compressor pin bushings will seldom be found worn too loose. Main gear knee pin bushings will sometimes be found worn loose. The most common fault with knee pin bushings will be misaligned bores, which prevent free pin movement from side to side during installation. The proper cure is align-reaming with a long-blade adjustable reamer, at a proper machine shop. Nose gear knee pin bushings will often be found loose (and must be repaired, to prevent shimmy). Worn gear bushings are best replaced with Owner Produced Parts by a local machine shop. If you find and purchase these bushings from Beech, you will find that the new bushings and mating pins must be taken to a local machine shop anyway, as the bushings are deliberately made undersize on the ID. The expectation is that they will be custom-sized for the used pins, for the best fit.
– Inexperienced mechanics will discover that the guide hole (in the upper casting) for the stack tube is very loose; and often they will also notice a slightly egg-shaped wear on the thrust side (maybe another 1/32” to 1/16”). They may sometimes declare the gear unairworthy for that reason. What they do not understand is that the hole is deliberately made more than 1/16” larger than the nominal 1” stack tube OD. This is because the compressor plate and tube travel is not completely vertical. It travels through an arc as it moves up and down, as the trailing link travels about the knee pin. If the hole was made snug, the tube would bind and break, as it tried to rock in the hole. In addition, the donuts are basically self-centering inside the housing. Guide hole wear is not excessive until the donut washers show abrasion marks on the inside of the casting. These top castings are unavailable in a totally unworn condition; and no new ones have been made in many years. Just apply grease at the hole and on the tube, during reassembly, and the assembly will last for a great many more years, unless you see rub marks inside the casting from the bonded donut metal washers.
– Note that this is the time to replace your brake lines, if they are ten or more years old; or if they have no proper TSO tags on them (which identify the lines and assembly date). Don’t forget about the brake lines inside the cabin, at the master cylinders and parking brake valve, and at the fuel tank connection from the wings. If you purchase new hoses locally, make absolutely certain that they have been pressure-tested and carry the TSO tags. Brake lines should be tested to at least 2,000 PSI, and higher is better; the hose itself is usually rated to 3,000 PSI. I can obtain new professional hoses for BAC members, at a slight discount off list. Don’t bother trying to get these hoses from RAPID (price and availability issues).
– Since you will be bleeding the brakes anyway, now is also a great time to install new caliper O-rings (and to polish the piston and bore), if there is no indication of recent caliper repair (as opposed to just lining replacements).
– Unless recently performed, don’t forget to pull the wheel bearings for cleaning, inspection, re-greasing, and reinstallation. Tire replacement may also be warranted, while everything is apart.
And now, where to get the donuts.
You can find out everything about the new donuts by doing a BAC search on ‘alternative FAA-PMA gear cushions’, and reading the posts. I have pasted in part of the info for you, below. The short story is that you need three sets of cushions and four Jo-bolts (J-Bolts are for fixed main gear only). These can be ordered directly from AEC on their website (or by phone). The link is on BAC. Your BAC Member price is $360 per set (you need three). For comparison, The Beech price is $674 per set.
You will save $942 on the three sets. You’ll need four Jo-bolts at $29
each, totaling $116. The total for the cushions and Jo-bolts will be about
$1,196. As a BAC member, you may order these parts directly from AEC, by putting your BAC Member Number in the Company Name field. You pay the same price that Aircraft Spruce pays; and Spruce resells them for $497/set (fixed gear).
I sell the set of three stainless steel pins to BAC members for $10, shipping included. I just need your mailing address if you decide to order the pins. Before you do, please take a look at the BAC Classifieds (General Resources, Classifieds), as I also sell things like o-ring kits. There will be no shipping charges if you order additional items along with the pins.
The alternative FAA-PMA gear cushions (donuts) are now available from AEC.
Kamran hopes and expects that the automated website ordering will be working on Monday; http://www.aec-inc.com/. My understanding is that the online ordering capability will include a credit card option. Note that if the online capability still does not work by the time you try it/need it, Kamran can accept manual orders by phone, but they will require non-card payment methods. Evidently AEC isn’t set up for card orders in their office.
Below is the parts list and AEC pricing; I have added the current RAPID pricing in red. The prices do not include shipping cost; you will have your option of preferred shipping to your location. If you are outside the USA, and as a BAC member you have purchased small parts from me before, please contact me offline if ordering from AEC is a problem for you.
One set, AEC-169-380003-7, 8 pieces/set, $360.00/set. (RAPID $674.26) (Supersedes the 169-380003 basic number part. These fit all three fixed-gear legs, and the nose gear on the Model 24 retracts). You need three sets to complete a fixed-gear airframe.
Two Jo-Bolts needed per landing gear side, a total of four bolts. Standard size NAS1669-6L7, $29 each (RAPID $30). The RAPID price on these is actually reasonable, but many owners have been paying local shops as much as $50 for these bolts. While the parts book shows one long bolt, the actual application uses two short Jo-Bolts; this was changed around 1964-1965. The Jo-Bolts will expand to fill their holes, to keep the gear very tight to the wing. The single long bolt will quickly begin fretting in its hole, allowing play to develop between the gear and the gear bracket. This is the subject of a Beech Service Instruction.