Frozen/Broken Bolt on Landing Gear Cylinder Spar Attach - Need Dimensions for Drill Jig

bednarkm

I am the owner of 1968 PA-28-140. In support of further wing repair, during my attempted removal of the RH landing gear cylinder, I experienced a frozen lower spar cap attachment bolt which, during the attempted removal process, broke off at the bolt's lower thread junction (just at the surface of the wing skin)(FYI, deep soak with Kroil, et al, did no good). Unfortunately, this will now require me to drill out the bolt. To prevent damage to either the spar cap or the landing gear cylinder, I need to create a drill jig and, for this, I am looking to see if anyone has a drawing or sketch detailing the dimensional spacing between the four cylinder to lower spar cap AN4 attachment bolts (X<--?-->X<--?-->X<--?-->X). Can anyone in community provide?

(FYSA. I also sent a like request to Piper Aircraft).

empannin

Could you also weld to the remains a new nut? Could you send a pic? There are also mobile specialists in bolt extraction too.

bednarkm

Unfortunately, it broke off at the wing skin surface. The underlying issue is that the body of the bolt is frozen in the casting, and the inboard location of the (recessed) head within the wing only allows use of a stubby (short) socket wrench.

bednarkm

Low_Wing.jpg

Here's a photo of the issue.

empannin

Hi, I would take one of the good bolts and do some trials. One path would be to center punch it and then drill out a hole for a bolt extractor.

This one scored well in testing: https://www.boschtools.com/us/en/boschtools-ocs/screw-extractor-sets-bspe6d-189600-p/

Another option would be to create a drill guide with wood if you would prefer drilling it out.

The third path would be to weld a nut to it.

I think it would be possible for a welder to weld to that sheared off head and put on a new nut. Perhaps with a tig/mig welding set up? I am a horrible welder but I see these videos all the time. For a flush break see 8:30. The first technique is a neat idea for a a buried break where you need to protect the threads.

https://www.youtube.com/watch?v=-8N0y0jVAng

griff390

The copper tube is an excellent method for aircraft. MIG weld won't stick to copper, the tube will (somewhat) protect the surrounding aluminum, and as Eric mentioned, once built up past the skin, you can weld a nut on the end and remove the broken stub with a wrench. Don't use anything galvanized because it releases toxic fumes when welded.

Generally, the heat from welding usually creates enough expansion to break the bond. The nut simply allows you to put a tool on it.

Rust and corrosion...they're nature's thread-lock!

bednarkm

Unfortunately, welding is not an option as the bolt sheared off flush with the wing skin. Looks like "a drilling we will go". I need to be careful to not screw up the main spar as I understand its $15K to replace (or obtain a used replacement right wing). Keeping my fingers crossed!

empannin

There are also mobile machine services that specialize in extraction. You might check locally and see. It is possible they will decline if aviation related but they may also offer feedback on approaches.

For welding, flush with the wingskin would be ok if shielded. the Copper pipe approach and MIG would be appropriate. (Shield the area and any threads exposed with Cu. The energy in this type of weld is very concentrated to the weld itself vs surrounding parts.

With my welding experience (or lack of), I would many practice attempts first in a scrap aluminum cylinder head.