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Ever since Bob Mika had a bolt break where the landing gear rod connects to the motor mount I thought it would be a good part to replace at every 100 hrs. Mainly because sometimes my landings a little bouncy if you know what I mean. Anyway this last annual I had a 100 hr on the plane and had the new bolts in hand but for some reason didn't get them installed. 25 hr later I had the cowling off for an oil change and noticed the bolt slid out about a half an inch from the motor mount. I was able to pull half of the bolt out with the other half held in by the fire wall. These were the AN updated bolts not stainless. From now on I am making this a preflight check item and will be replacing all 4 landing gear bolts every 100 hrs.

I had a bolt break at about 100 hours. It caused my wheel to rotate onto its side and destroyed my wheel pant.
Sent pictures to Sonex and they thought it was due to a burr and fretting.
I'm now changing them every oil change. They are cheap.

Just to clarify, this is the bolt where the engine mount holds the gear leg in? You have to pull the cowling to check it...?

How would you replace it? I probably couldn't get that bolt out without pulling it with the engine installed ....much less if half of it broke off....

Someone else suggested getting bolts I could safety wire at both ends....now you are making me understand the wisdom of doing so!

Do you have photos?


Robbie Culver
Sonex 1517
Chicagoland
Tails and Wings complete - finishing fuselage.
N1517S reserved

The upper bolt in the engine mount. My bolts go in from the engine side with a castle nut and cotter against the firewall. It's a pretty quick swap.
I think unless the bolts are a tight fit, they vibrate and fret in the holes during flight when the legs are unloaded. My last swap showed minor fretting on one.

I had to put my bolts in from the firewall side. There wasn't clearance for a castle nut on the firewall. Mine were a snug fit, and I deburred inside and out. Hope they don't break!

Have 5/16 inch bolts in mine. Leg wrapped in SS shim stock and bolt tightened just enough to insure nothing is loose. No reason to worry with those, but a bit tricky to accurately drill out.

David A. Sonex TD.

Bryan Cotton wrote:I had to put my bolts in from the firewall side. There wasn't clearance for a castle nut on the firewall. Mine were a snug fit, and I deburred inside and out. Hope they don't break!

Same here. I figured if I ever have to remove them, I'll just drill holes in the FW and insert/remove from inside, then patch the holes. I had to more or less hammer the gear legs into final position, I don't foresee the bolts having to do all that much work.

DCASonex wrote:Have 5/16 inch bolts in mine. Leg wrapped in SS shim stock and bolt tightened just enough to insure nothing is loose. No reason to worry with those, but a bit tricky to accurately drill out.

David A. Sonex TD.

After my broken bolt, I thought about up drilling to 5/16, even bought a new bit and bolts to do it. But I decided to try another set of 1/4s and see how they hold up. Like I said, after 50 hours one showed some fretting, so I replaced both and bought 10 more.

Yes, these bolts are the top two bolts in the gear legs. The castle nuts are between the mount and firewall and are easier to replace before the bolts break in half. To replace, put the plane up on blocks to take pressure off of gear leg. Tap the broken bolt out toward the firewall, then cut it off and tap the rest of it out. This was the only way I could get the half broken piece out without removing the motor mount from the fuselage. It was a pain to remove it, so that is why I want to catch it before they break and cause bigger issues. I usually always do a preflight inspection with a flashlight to look up thru the lower opening to check engine components and visually check the gear bolts at the same time. I am going to replace all four gear leg bolts every hundred hours or at annual. Replacing both top and bottom bolts is cheap insurance, like John G. said previously.

Excellent. Thanks for clarifying. I will keep an eye on mine.


Robbie Culver
Sonex 1517
Chicagoland
Tails and Wings complete - finishing fuselage.
N1517S reserved