In between activities over the long holiday weekend, I spent some time working on the nose gear. I found the nose gear difficult to rotate once assembled. It appeared to be binding on the split bushings used in the lower mount. I think the split bushings are created from a whole bushing cut in half, but the kerf of whatever blade was used removes enough material such that the split bushing is no longer a perfect circle, and reduced in diameter. Because of this, the bushing was acting as a clamp rather than a bearing.
I put together a short YouTube video to go along with this update:
I had to turn to other Sling builders on the Facebook group to see how to address this. All of the responses indicated two issues to address: fit of the split bushings, and also alignment of the bushings in the upper and lower mounts.
On the topic of upper-lower alignment, I’ll share the input I got from Evan Brunye, who is building a Sling Tsi and has a quite excellent video series on YouTube documenting his build. His advice:
“Take off the lower mounts. See where the gear leg wants to naturally rest when only the top bushing is in position. They weld the two sections together from 2 separate jigs, so they don’t seem to like to align properly. Check also to make sure the leg in the top bushing rotates freely at this time.
It’s possible the retaining rings are trying to put too much pressure on the split bushings on the bottom. Remove the top bushing and only have the lower ones in place, basically the opposite of step 1. Check to make sure the leg rotates smoothly in just the lower bracket. Also check to see how it aligns to the top location.
Now you see the natural resting spot, if it slightly to one direction, you’ll want to very slowly sand the inside of the bushings to allow it to move that slight bit over to become centered. If it seems that the clamps were the issue, you can try to grind out a small amount of material from the inside radius to allow a slightly looser clamp action.
Load it up with grease! It helps more than I would have expected.”
Following the steps above, I found the upper and lower mounts to be pretty well aligned on my motor mount, so I didn’t make any adjustment to the upper bushing. In step 2, I found that the leg wasn’t rotating smoothly in the lower bracket at all. Instead, the bushing was rotating with the leg, because it was being clamped too tightly.
There were a variety of techniques discussed on how to grind down the bearings; I chose to go with sandpaper wrapped around the gear leg, since the leg is already the correct diameter. As shown in the next few photos, my goal was to return the split bushings to the correct shape and size. I used coarse grit (120) sandpaper for initial removal in the longitudinal direction, then two passes to smooth it back out: medium grit (240) in the in the axial direction, and then fine grit (600) in a random orbital motion.
I used a trial-and-error process to determine when I had ground the bushings enough. Once I was satisfied the gear was rotating smoothly, I attached the leg to the motor mount, and then the motor mount onto the firewall. I now have all three wheels attached; it’s almost time to drop the plane onto its wheels!
One thing I decided to do before dropping the plane onto its wheels was to install the main gear close-out skin. This took a little bit of time since I was working upside down. I had already riveted the main gear box channel to the floor skins, so first I had to drill out those rivets.