Installation Instructions: Improved Nose Gear Scissor (Drag) Link Bushings

By Robert Pastusek

BACKGROUND: The Lancair IV-series aircraft incorporated different retractable landing gear assemblies than previous models. The three-piece nose gear scissor links used on the IV-series contained ¼” (AN4) drilled bolts that acted as pivots between the single-piece upper link and the two lower links. Due to builder difficulty in installing/adjusting this critical pivot joint, Lancair modified the lower links with introduction of the Legacy kit (which used the same parts) to include a bronze bushing that acted as the pivot and replaced the drilled and cotter-pinned bolt with a torqued AN4 tension bolt. Lancair provided the new parts with all Legacy kits after about 2006, and as an upgrade under Service Bulletin SB077-0518 for Lancair IV models.

The first issue that came up was that some IV owners installed the new lower links and bushings using the instructions contained in the original IV build manual. Specifically, they used a drilled bolt and castle nut/cotter pin to loosely join the upper and lower links. This allowed the bronze bushings to rotate on the bolts rather than on the lower link as designed. These incorrect installations allowed the bushing and bolt to wear rapidly, resulting in at least six documented nose gear collapses. The second issue, that took a bit longer to identify, was that even when installed correctly, the bronze bushing material was too soft to absorb the nose gear touchdown impact (especially in the IV models) and allowed the bushing to swage itself to the lower links. This caused the torqued bolt to loosen and become the pivot. Tightening the bolt typically locked the scissors linkage, either preventing gear retraction or loosening the bolt with each gear cycle so it again became the pivot point. As wear on the bolt/bushing increased, the over-center point for nose gear retraction moved from the designed pivot point to the point of contact between the ears of the lower links and the upper links. This defeated the “over-center” function of the scissor links assembly and allowed the gear to retract upon touchdown under some conditions—specifically with failure of the primary hydraulic system and/or a weak emergency extension gas spring, or a hard touchdown of the nose gear.

As long as both the hydraulic system and gas spring work together as designed, their combined force is typically enough to keep the gear from retracting. If the hydraulic system malfunctions, or if the gas spring loses pressure, the touch down impact is enough to collapse the nose gear. We documented at least eight such failures from 2016-2022. Expensive; and it consumed a lot of props!!

In 2022, LOBO asked Conrad Huffstutler to investigate this problem. Conrad quickly designed new lower links to eliminate the side load on the pivot joints and offered these parts with Lancair Service Bulletin 078-0722. Be sure you use Rev B, dated 10/31/2022 from the Lancair website, as earlier versions had significant errors. The new links provide an improved structural pivot and should permanently fix the above issues; this is one acceptable solution. Two lesser-cost alternatives are available, but both incur the requirement to annually disassemble and inspect the nose gear retraction (scissor linkage) assemblies. As one option, the pivot holes (2) in the upper linkage can be precision-drilled to 3/8” and AN6 drilled bolts with castle nuts/cotter pins used to replace the bronze bushings. (If you have the original scissor links without bronze bushings installed, you can precision-drill both the upper and lower links to accommodate smaller, drilled AN5 bolts and castle nuts.) Carefully follow the original Lancair IV assembly/adjustment directions if using this method. A second alternative is to replace the bronze bushings with form/fit/function identical parts made from 303 stainless steel. This harder material will not deform as easily as the bronze and should provide satisfactory service, although no long-term functional testing has been performed with this material. These SS bushings are available at no cost upon your personal request to Bob Pastusek (R.Pastusek [at] lancairowners.com). LOBO provides these without any warranty or representation as to their function. If you find these useful, a contribution to LOBO would be appreciated.

I encourage you to replace the bronze bushings if you have them installed on your aircraft. They WILL fail eventually. If you choose to replace them with either alternative to the new Lancair lower scissor links, you must inspect and lubricate the scissors linkage at least annually. I recommend you use the detailed instructions below for installing the SS bushings and for inspecting/testing your retractable nose gear components.

SS BUSHING INSTALLATION: The parts package LOBO provides contains form, fit, functional replacements for two bronze bushings used in the nose strut lower scissor links on some Lancair IV and all Legacy aircraft, and appropriate attaching AN4-12A bolts with steel locking nuts and washers. Reference the picture below to identify the affected parts. If your aircraft doesn’t have the pictured bronze bushings installed, DO NOT proceed with this instruction; these parts will not fit your unmodified scissor links. See the background above for alternatives.

NOTE: These instructions presume a working knowledge of Lancair aircraft systems, appropriate tools, and general aircraft maintenance procedures. If you don’t have these skills and tools, please seek the assistance of a qualified aircraft mechanic. The instructions are written specifically for the IV and Legacy models and are not applicable to other Lancair models.

NOTE: Some lower scissor links (pictured below) were made from cold-rolled, as opposed to the specified hot-rolled ¼” steel plate. The cold-rolled parts are dimensionally thicker (0.27”) versus the hot-rolled (0.25”) parts, and these SS bushings WILL NOT WORK on the thicker parts. If you have the thicker lower scissor links, see the options in background above.

In service, the bronze bushings have proven too soft to absorb the impact generated during nose wheel touchdown, causing them to deform and wear excessively. (Note the space between the bolt and the bushing in the second picture.) This allows the bolt to become the pivot rather than the bushing, and to loosen with gear retraction/extension. Simply tightening this bolt typically locks the pivot, preventing nose gear retraction—and could prevent nose gear extension. If not replaced, these defective pivot bushings will eventually wear enough to change the over-center point of the joint and allow the nose gear to retract during landing.

Verify your nose strut scissor links have the pictured bronze bushings installed. Do not proceed until you can confirm this.

1. Securely block the aircraft and raise the nose wheel off the ground.
2. Bleed off any pressure in the hydraulic system.
3. Remove the lower engine cowling and disconnect the nose gear door linkage.
4. Remove the long AN5 bolt securing the two lower scissor links to the nose strut. An assistant to push up on the lower scissor link to relieve pressure of the gas spring helps in removing this bolt.
5. Test the gas spring. (This step is optional)
   1. Remove the gas spring from the upper scissor link.
   2. Test the gas spring for a minimum measured compression force of 90#.
   3. Re-install the gas spring or a replacement, taking care to safety the attachment bolts, and confirm that the strut ends pivot freely at the attachment points. Note that there is typically a small bronze bushing to transition the metric holes in the strut ends to the US-size hardware. The strut ends should fit on the attachment bolts with minimum free play.
6. Remove the two lower scissor links from the upper scissor link assembly, carefully noting the orientation of parts and attachment bolts. A picture before disassembly helps...
7. Test the spherical pillow block bearings attaching the top of the nose strut to the motor mount for free pivoting and strut side-to-side movement. (This step is optional)
   1. Ensure that the nose strut swings freely within the pillow blocks that attach it to the motor mount. Lubricate if necessary.
   2. Check the side-to-side movement of the nose strut where it attaches to the motor mount by pushing the strut from side to side. Any detectable movement (more than 0.01”) indicates the need to remove this side free-play.
   3. If a fix is needed, disconnect the hydraulic cylinder from the strut. Remove the pillow blocks and strut from the motor mount.
   4. Install circular bushings (a piece of large diameter AL tubing?) on top of the spherical bearings in the pillow blocks as needed to press them securely into the bottom of the pillow block. The top edge of the fabricated bushing should be flush with the face of the pillow block.
   5. With the pillow blocks fully installed on the strut pivots, check the spacing between the pillow blocks and the corresponding motor mount attachment faces.
   6. Make two equal-thickness shims from aluminum sheet to fully fill any space between the pillow blocks and motor mount. The pillow blocks should be a tight/interference fit between the motor mount attachment plates with the shims installed.
   7. Lubricate the spherical bearings and re-install the pillow blocks with one spacer between each block and the motor mount.
   8. Secure/torque all attachment bolts.
   9. Confirm that the nose strut pivots freely at the pillow blocks. Do not proceed until this condition is satisfied.
   10. Re-attach the hydraulic cylinder.
8. Attempt to rotate the bronze bushing in each of the two lower scissor links. Each bushing should rotate freely in its respective lower scissor link. After a few landings, the bronze bushings “swage” themselves to conform to the hole in the lower scissor links and won’t turn freely as designed. They normally fail this test after fewer than 100 landings, and the linkage then pivots on the bolt, causing it to loosen and wear rapidly.
9. Remove the bronze bushings from the lower scissor links. You may need to use a drift punch, being careful not to damage the steel scissor links, and especially the existing holes where the bushings were installed. Clean the scissor links and remove any paint where the bushings/washers make contact with either the upper or lower scissor links.
10. Lightly lubricate the new stainless steel bushings and test fit them into the lower scissor links. The new bushing should rotate freely in the lower scissor link without excessive free play. If the hole in a scissor link exceeds 0.380”, or the new bushing does not fit snugly in the hole, consider replacing the link.
11. Verify that the new stainless steel bushings protrude through the hole in the scissor link by approximately 0.001-0.003.” If the bushings do not protrude through the scissor link when fully inserted, do not proceed with this installation, as the joint will not pivot freely when tightened. (This will be the situation if you have the thicker, cold-rolled lower scissor links.)
12. Re-install the lower scissor links to the upper link, using the new AN 4-12A bolts and AN363-428 locking nuts. Place a standard washer under the bolt head and under the nut. Place a thin washer between the upper and lower scissor links. Note that the bolts need to be installed from the inside out, with the nut on the outside of the assembly. This provides clearance between the nose strut and pivot bolts when the gear is retracted. Torque these bolts to 70 inch-pounds, using a torque wrench!!
13. Verify that the lower links will pivot on the upper link through the range of motion required during gear retraction. THIS IS A CRITICAL STEP. Do not proceed until this condition is satisfied!
14. Check the over-center relationship of the upper and lower scissor links by aligning a flexible straightedge between the center of the upper scissor link attachment bolt at the motor mount and the center of the bottom lower scissor link mounting holes, with the scissor links fully extended against their respective stops. The center pivot bolt/bushing should be slightly “over-center.” The acceptable over-center distance is 1/8”- 3/8”. THIS IS A CRITICAL STEP. Do not proceed until this condition is satisfied! Please call me if you have any question about this test!!
15. Clean, lubricate and re-install the lower scissor links to the nose strut. As with removal, an assistant to help push the lower scissor link into position against the gas spring is a great help. Note that some nose struts have a bushing inside the tube that’s welded to the strut. The lower scissor links are bolted and torqued to this bushing. Other struts used a pivot bolt through the tube that’s drilled and secured with a castle nut and cotter pin. Be sure to note which type you have and reinstall accordingly! Recheck the security and safety of all fasteners!
16. Re-install the lower cowl and nose gear door linkage.
17. Conduct a gear retraction test to verify nose gear operation without binding and full nose gear door closure. THIS IS A CRITICAL STEP. Do not proceed until this condition is satisfied!
18. Make a logbook entry of this modification. Weight and balance are not affected.
19. Add the requirement to lubricate these bushings and verify the security of the pivot bolts after ten landings and at each subsequent condition inspection. Any looseness of more than 1/8 turn of the pivot bolt nuts is cause for disassembly and inspection IAW paragraphs 12-16 above. Specifically, tightening the pivot bolts without checking that the links swing freely after tightening can prevent nose gear retraction or extension.