Firewall Forward

December 16, 2012

Fixing a Problem with the Main Gear Legs - 2.0 Hours

Back on December 20, 2009, when I first assembled the main gear legs together with the weldments that hold them in the fuselage and drilled them, I made a big mistake. I was relatively inexperienced at the time, and in my excitement and haste I failed to read the plans carefully enough. Now that I'm getting ready to put the airplane on her gear, I found that the AN5-22A bolts that hold the gear legs in the weldments don't fit right. They're sloppy. The holes I drilled are too big! Since the entire assembly... the gear leg, wheel, brake and tire... are held in place with this single bolt, it's critical that it has a tight, close-tolerance fit. A little sloppiness in the bolt hole translates to a lot of movement (and potential shimmy) down at the wheel end of the leg. All that shimmying around wears on the holes in the weldment and makes them even bigger, so the problem can potentially become even worse! I should have read the plans more carefully and NOT used a 5/16" reamer to drill these out. As you can see in Drawing 34A, you should use a 0.311" reamer on these holes.

I didn't have this reamer at the time, but I bought one later to use to drill the rear wing spars when I mated the wings. My advice, do NOT use a 5/16" reamer or drill bit! Get yourself a 0.311" reamer. You're going to need it anyway when you mate your wings and drill the rear spar holes.

My solution to this mess? I had to order new special hardware, the next size up, along with a new reamer, and drill this all over again. With shipping and all, it cost me almost $100. Expensive mistake! I guess I should take the opportunity, though, to express my gratitude and put in a plug for Genuine Aircraft Hardware Co. Mr. Tom Brink, the president of the company, went out of his way to talk to me, email me, and communicate with me and help me find the right solution to this problem. If you need aircraft hardware of any kind, this is the place to go. These are great people! I ended up ordering a 0.3265" reamer, and a pair of NAS6605-29X bolts, along with the associated washers and lock nuts. Tom suggested I should drill with the reamer while the parts are together, rather than separately. This is why I went ahead and put the plane on her gear recently.

Okay. So how do I get the bolts out that are now in there, and run the reamer through, while the gear leg is still in place? I worried about this. The last thing I wanted to do, if I could avoid it, was to take the gear leg weldments out of the plane. My idea was to use the hoist I have on hand, and lift up the front of the fuselage just enough to take most of the weight off of the gear, while it's still on the floor. I was hoping that if I did it just right, I could slip the bolts out without the gear leg slipping out of place. I worried about the exact positioning, but it was easier than I thought. Here's the hoist in place after lifting the front end up. The wheels are still on the floor but almost all the weight is off of them.

I was very pleased that the AN5-22A bolt slipped right out into my hands, with no trouble at all. The gear leg didn't slip or move! So I grabbed my right-angle drill, with the new reamer in place, lubed it up with some Boelube, and went for it. The right-angle drill was the right tool for this job. A straight drill wouldn't fit very well in this tight space.

This, too, turned out to be easier than I thought. Wow. How often does that happen? This reamer is a piloted reamer, and the smaller diameter pilot on the front went right in, assuring that nothing would move now. And it functions as a guide, of course, so you get a very straight, clean hole. The reaming was solid and effective, but it went through with little trouble. Nice! So far, so good. I temporarily slipped the original AN5 bolt back in while I went around and did the other side. Then I hoisted it all up, took both gear legs off the plane, deburred and cleaned everything up, lightly put a thin coat of grease on the bare metal parts of the gear legs, and installed them with the new hardware.

The new bolts were close tolerance, alright. The fit was very tight, as you would expect, but they went in. I used a rubber mallet to persuade them into place. There is no wiggle room whatsoever now. I'm glad to get this done. This has been bothering me for a long time. With the tapered pin in the nose wheel gear leg, I feel very good now about my landing gear being solidly in place.

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