What do I need to consider, or have done, to get the play out of my nose gear? Or to get the landing gear repaired?
(Search strings: nose gear play, nose gear repair, landing gear repair, nose gear bearing, replace donuts, donut replacement)
Technical Editor:
There is a Beech-approved method for stabilizing the lower bronze bearing, by bedding it in epoxy. Most mechanics don’t even know about it, because they do not maintain currency on all the SIs/SBs for the planes. While it was never formally approved by Beech (for economic reasons), an old (now-deceased) Beechcrafter also told me how to secure the bearings (top and bottom) by using MilSpec NAS548 structural-steel countersunk 6-32 screws (eliminating the crappy roll pins). Based on the guidance in AC43.13-1B, Paragraph 7, roll pins should never have been allowed in this kind of application (unsecured parts, pins bedded in alloy versus steel). The combination results in solidly mounted and bedded bearings, both top and bottom. With the proper shim in place, lubricant has to come out between the bearing surfaces, rather than between bearings and castings (as it does with the original loose roll-pin set-up). If the gear is clear of the ground, the grease is forced to exit between the primary wear surfaces, which both cleans and re-lubricates these key wear points. The original bearing setup lasts for maybe 300-400 hours before it becomes too loose. When I set them up, they will typically go 2,000 hours, if properly greased with a Lithium-based grease (not any Microgel-based Aeroshell grease), every 25 hours as specified in the Shop Manual, and with the aircraft on jacks.
The expense for thorough repair really isn’t all that bad in the grand scheme of aircraft expense, cost-wise, as long as no major parts are found to be unairworthy. I have not yet had to condemn any expensive parts, with the exception of one $400 bearing that was really chewed up. The new spec is .150” flange thickness; that one was not only worn below .090”; it also had asymmetric wear, because someone had let it go with too much play, for too long a time. Several people have sent me gear that another A&P had labeled unairworthy; but they were actually still serviceable. The other technicians did not have the experience to realize what the wear patterns indicated (on our planes), and did not have any of the Beech data on which to form the opinion; they were just going by the assumption that some clearance meant ‘bad’. I just returned a repaired, powder-coated nose gear, for a 1966 Musketeer; the total bill was $1,245. That included new donuts, all four pin bushings replaced, the pins polished, complete stripping, Magnadyning, and powder-coating, one new pivot bearing, both upper and lower bearings screwed to the attachment points (threaded and tapped holes along with countersunk bearing holes, rather than roll pins), lower bearing epoxy-bedded, the proper shims installed, and all new hardware. While I cannot call it an ‘overhaul’ or ‘rebuild’ (only a ‘repair’, until Chad and I can establish a Part 145 Repair Station for these landing gears), he got back a gear that looked better than new; with a finish that will hold up better than new; with bearing retention far better than the original; and ready to bolt in. That gear will go for 2,000 hours or more, if it gets greased every 25 hours as specified, with the right type of grease (Lithium, such as Aeroshell #33), and with the plane on jacks. All it might need is an added shim every few hundred hours; maybe an hour’s job, with no gear removal. The original nose gear set-up won’t go more than a couple of hundred hours, before needing re-shimming due to bearing wear, even if every single piece, including the housings, is brand-new. And in the meantime, the loose bearings will have been grinding away on the column in the upper housing, until it becomes unrepairable. My normal basic labor on the nose gear is $350 to $450 (1963 models); the process for the radiant-cured powder-coating is $150; the donuts average $375/set with shipping. There are modest additional expenses on each gear for the four pin bushings and new hardware. The gear will probably look and work like new for a long time; probably for the remaining airframe life, if properly greased.
I used to quote $250 labor for a main gear, and $350 for a nose gear. Now I can only say $250 to $350 per main gear, and $350 to $450 per nose gear. At my personal rate of $35 per hour, I’m not even breaking even on my time on these. It is a rare nose gear, for example, that doesn’t take me far more than twelve hours to get disassembled; re-cleaned; parts examined; pins polished; drillings cleared; stripping, Magnadyning, and powder-coating; bushings custom-fitted to the pins on my lathe, and installed; bushings align-reamed with a long-shaft adjustable piloted reamer, for a perfect pin fit; new donuts installed; pivot bearings re-worked with drilled and tapped holes; lower bearing epoxy bedded; upper bearing properly shimmed and assembled; and the gear fully reassembled.
I also cannot predict what a given gear leg will need, in order to complete a repair. In most cases, I expect that new gear cushions (donuts) will be required. That normally means that the owner needs to order those from AECI, and have them shipped directly to me. Beyond the donuts and powder-coating, I can’t know in advance what else will be needed.
Normally the gear will all need knee bushings. List is $600 each (two per gear). The compressor plate pin often needs bushings as well; List is $600 each (two per gear). The nose gear pivot bearing will normally require the big laminated shim (list is $53); and sometimes one or both main bearings will be needed. Those are also extremely expensive ($700 List for the standard size; higher for oversize), and I will normally contact the owner if I discover a badly worn or scored main bearing. Sometimes I am able to substitute a used-serviceable bearing, when I can find one (they are rare, but I have two at the moment). Unless they are really badly scored or corroded, I can usually polish out and re-use the pins themselves; that’s a good thing, as they are hundreds of dollars each List. I do stock a few, just in case, but have only had to sell two of them so far. Shipping cost, for a single large box, usually runs around $30 for a single gear; and about $50-$55 for a box containing all three gear. Insurance will add about $100 per $5,000 in coverage; my preference is for $10,000 on nose gears, half that on main gears.
In most cases, I am usually able to charge well below List for the parts; often in the range of 60%-75% of List (and occasionally less), due to New Old Stock still on hand. Just as I do for all the other parts I sell on BAC, I try to scoop up these parts when I find a batch at a lower price, so I can resell and save members money. There are some exceptions for which I have to charge List, or even a bit over List in the case of convenience sales items; but in most cases I charge far below List. The exceptions occur when I have absolutely no alternative but to pay List for the parts, in order to get them, to meet a need.
I can guarantee you several factors.
– You will not be able to get landing gear repairs properly made almost anywhere else. Few shops will have the Beech drawings, and the specialized tools such as the piloted adjustable reamer, to do the job properly.
– You will pay for as many or more hours of shop time, to get the same work done, but at a rate probably two to four times my rate.
– You will not find any other shop that will provide you with parts pricing that is well below List. They will get a 5% FBO discount on parts (from most suppliers), if they can find them; and they will charge you List (or more; some tack on a finder’s fee).
– No other shop will have the parts on hand, to complete the job with minimal delay.
Hopefully this gives you some idea of what is required for proper gear repair and maintenance. When properly repaired, and with proper lubrication (greasing with the gear leg hanging free of the ground), both mains and nose gear can go 2,000 hours (or more) without needing anything more than lubrication and possibly an added shim (and perhaps a new brake hose ten or fifteen years down the road). Most common field-repaired landing gears will seldom last more than 300 hours or so before developing excessive play, especially on the nose gear. As an example of my lifespan estimates, I long ago posted on BAC that the rolled door hinge replacements being shipped from the factory would not last more than 300 hours or so; and that the original Beech standard matching Mil-Spec extruded NAS40 hinge should be used. I recently received a note from a member who had just replaced a door hinge with the NAS40. He found the removed parts to be rolled hinge. He went back through his logs, and sure enough; a mechanic had replaced the original hinge, with the rolled Beech replacement parts, exactly 300 hours earlier (for the prior owner).
I hope this gives you what you are asking for, regarding cost estimates for landing gear repair. I cannot quote an exact cost for yours, unless you just want a number that is the maximum possible (assuming everything gets replaced except the castings). Doesn’t matter to me whether you send your gear; I have too much to do as it is, for a retired guy. Like everything else I do that is BAC-related, the landing gear repairs are just offered to help members get the job done right, at a much lower cost than would normally be the case. And without being at the mercy of technicians who do not know and understand the planes, and who typically do not have the Beech data to work from. I don’t do this work for anyone who is not a BAC member.
A recent classic example was a member whose A&P-IA had condemned the upper main casting on the nose gear, due to excessive stack tube hole wear. The member called me. The A&P-IA agreed to let me repair the gear, return it with a Repair Letter on my A&P license, and he would reinstall it. The alternative was a replacement salvage casting, if one could be found. One had been shipped in for $3,000, but the tube hole had the same ‘problem’; it was returned. When I got the casting, the hole size was only slightly larger than normal. The A&P-IA did not have the Beech drawings, and did not realize that, by design, the hole is made .125” larger than the tube. The tube travels in an arc due to the trailing link gear design. The tube has to be able to ‘rock’ slightly in its hole, or it will bind up. In addition, the stack of donuts is ‘self-piloting’ within the housing. The only time that the hole is too large is when the bonded donut washers begin to contact the inside of the casting. The poor guy had wasted close to $1,500 on this issue by the time he was able to send me the gear.
Addendum September 2008
On Sierras, the upper and lower yoke bearings are made of steel, part number noted below. The fixed-gear planes have these bearings as a machined area on the top and bottom of the gear attach section of the engine mount. The steel bearings typically do not suffer any significant wear, unless roll pins from the brass bearings come loose and score them. Mild scoring is not an issue.
The brass bearings, P/N 169-810016-3, list for $623… if you can find any. I have provided the data, if you wish to try to have some made locally; see the bottom of this note. I also have a copy of a drawing for the brass (actually aluminum-bronze) bearings, if it proves necessary.
The problem with loose bearings will be improved only very temporarily with new bearings; even if they are custom-made to fit a worn housing. If you look at the top of the column and the base of the column, you will see serious chafing where the ID and flange of the bearing chatter on the alloy. This should never happen. If kept snugly shimmed, any wear should be limited to the brass-to-steel junction. That does not happen as intended, because the bearings are not properly retained; they are just prevented from rotating by the roll pins. The bearings rapidly become loose on the roll pins, and chatter on the housing. To compound matters, since the bearings are not solidly retained, any applied grease tends to come out between the bearing and the shim; or between the bearing and the housing. The junction between the steel bearing and brass bearing seldom gets flushed clean with new grease.
Bearings are usually still serviceable, though there certainly are exceptions. You can find out by placing the upper into the upper steel yoke bearing, and ditto for the lower bearing. If there is only very slight lateral clearance between the brass and steel bearings, and the flanges are still more than .090” thick, your bearings are probably still OK. What is not OK is the bearing retention and the bearing shimming. The roll pins need to be removed (which is sometimes very difficult). The roll pin holes should be tapped (very straight) using a 6-32 tap. It takes a long-shaft tap to do the holes in the base of the column, where conventional tap-holders cannot fit. The bushings get their holes slightly relieved to clear the shank on 6-32 100-degree structural flat-head Phillips screws (I use NAS548; you cannot get AN509C in size 6-32). The bearing-side holes are then countersunk using a 100-degree reduced-diameter aviation piloted cutter, so that the heads of the screws are recessed about .025” below the surface.
The lower bearing has the column base covered with a thin film of structural epoxy, on the upper half of the radius (I like Marine-Tex, because it is reinforced, is white, and resists everything). The bearing is slid down on the column until it is bedded in the epoxy, then the screws are used to secure the bearing. Any extruded epoxy must be cleaned up with Q-tips. A little epoxy goes a long way. When properly applied, there will be no unfilled gap between the bearing and the housing column, nor between the bottom of the bearing and its seating area at the base of the column. The epoxy then cures overnight, before further assembly. If the lower bearing ever does require removal, a heat gun will release the epoxy bedding compound.
The top collar has its roll pins removed and the holes tapped. The bearing holes get relieved and countersunk just like the bottom bearing, but they do not need to be so deeply recessed. The proper shim thickness is selected, the holes are punched in the shim, and the bearing and shim are loosely screwed to the collar, The assembly is placed upside-down on the column for alignment, and the screws are secured. The bearing is then clamping the shims to the collar. The gear should be shimmed snugly enough to feel drag when rotating it by hand; but not so much drag that it prevents emergency extension on a Sierra. It will initially loosen up with about twenty minutes of taxi time, as the parts ‘bed in’; so you do not want to initially set it up loose.
You must be careful when snugging down the 6-32 screws, as they are pretty small. They have a slightly larger OD than the roll pins; and they are solid, not hollow and split. They do not have the ‘give’ that a roll pin can have, when loaded in shear. Both bearings will remain tightly in place. When the day comes that more shimming is needed, you just measure the clearance to get the additional shim size, remove the top collar, unscrew the bearing, add the shim, and reassemble. If you keep the shims snug, the mating bearing radius (brass on steel) prevents lateral motion. With the bearings properly secured, and the nose wheel hanging free for greasing, new grease comes out between the two bottom bearing wear surfaces (as it should), cleaning out the dirt and refreshing the lube right where it is needed. Then you lower the weight on the nose again, and add a couple of pumps to lube the upper bearing surfaces. Properly repairing the nose gear like this will enable it to hold up for a couple of thousand hours, with nothing more than one or two added shims. This assumes it is being properly greased, and that re-shimming is not let go too long (maybe an hour’s job).
I have the equipment to do this, as well as the equipment to install and align-bore new knee bushings for the knee pin. I have repaired dozens of these landing gears, nose and mains. If you send me your gear, complete with assembled yoke assembly (or all of the parts), I send it back in excellent condition, with a letter of repair over my A&P signature. I am not a Repair Station, so I cannot call it an overhaul or rebuild; only a repair. For the same reason, I cannot do exchanges; I can only fix your gear. If you wish, I can also have the gear parts bead-blasted, re-Magnadyned, and white powder-coated, for a $150 fee. My labor charge for a nose gear ranges from $350 to $450. Parts and powder coating usually add another $300 to $600, assuming no crucial parts are unusable (such as bolts broken off in the top collar). If I have to provide new donuts, it usually adds another $380 or so, depending on shipping charges from AECI. You can also order the donuts yourself, and have them shipped here (AECI is accustomed to that). If you wind up installing new donuts yourself, note that you cannot use the value in the Shop Manual for height setting. You must tighten down the big stack tube nut only until the top thread barely exits the elastic locking portion of the nut. Otherwise the retracted nose gear will leave tire chafing marks on the hydraulic lines in the LH side of the nose wheel well.
My nose gear repair bills have ranged from a low of about $800, to a high close to $3,000 (had to locate an upper housing due to cracks). Most run around $1,000 or so, if you provide the new donuts (if the donuts are more than ten years old, I won’t reinstall the old ones) You get back a gear with new donuts, new pivot bushings, new stack tube hardware, new Clevis pins, etc. The main bearings are reworked as described. Shipping usually runs $30-$40 each way. If you are interested in this, let me know.
By the way, when you reinstall the top cover, make certain that you do not over-tighten the MS20073 10-24 drilled-head bolts. They are not structural grade, and are easily broken; they just get lightly snugged into place, and are then safety-wired. For the same reason, examine each one carefully after cleaning; look for any signs of stretched threads. That means that the bolt is cracked, and will break when you reinstall it. Also look very carefully at the tie link between the cap and the steering adapter. The rod ends are often bent or cracked by poor ground handling. And finally, look very closely at the lower drag link, and the junction between the link and the boss on the aft side of the yoke. If there are any indications of rubbing, you must use a Dremel to re-clearance the boss; Beech sent out a number of them with bad machining. If the lower drag link has been rubbing on the boss, the link needs to be stripped and dye-checked for cracks. Otherwise you are at risk for a nose gear collapse.
169-810016-3 Bronze pivot bearing, ID 3.5”, OD 3.640”, standard size
CO B73751-1 Bronze pivot bearing, ID 3.5”, OD 3.630”, .010 undersize
CO B73751-3 Bronze pivot bearing, ID 3.5”, OD 3.635”, .005 undersize
CO B73751-5 Bronze pivot bearing, ID 3.5”, OD 3.645”, .005 oversize
169-810016-5 Original .005 oversize bearing; superseded by the CO B73751-5
169-820016-9 Steel pivot bearing, mates with bronze; top and bottom of yoke assy
50-820024 Laminated shim; ID= 3.50” , OD= 4.25”, .045” thick
The -3 bearing is manufactured from, cored bearing bronze, QQ-B-671 type 2 class 3
QPL Specs
Family ALUMINUM BRONZE
DIN CDA C95400
ASTM1 B505,,
ASARCON
SAE1 B505,,
AMS
FEDERAL1 QQC390 G5,QQ-B-671, CLASS 3
INGOT # 415
OTHER DESG. ALUMINUM BRONZE 9C
MILITARY1 MIL-B-16033, CLASS 3,