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Upper engine mount

YellaDawg

Well Known Member
Sponsor
Couldn't find a thread on this, so I'll ask. The upper engine mounts spec a An6 bolt which is 3/8". The engine side of the mount hole is 1/2" which allows a lot of wiggle wobble for the bolt. I understand the firewall side of the mount is 3/8" and has to be reamed. That leaves about 1.5" of the engine bolt with the wiggle wobble. Mothership says the mount is for tension, not shear. Why not both? I made a bushing to take the wiggle wobble out, just seems odd to me to have that space, it would have been very easy to either provide a bushing or leave more mass in the hole. I feel much better with the wiggle wobble gone, and a slightly larger diameter washer.
 
I don't have a -14, but I did help a friend hang an engine on one a couple of weeks ago. Since no one else has responded, I'll take a shot.

My -7 plans spec an AN-7 (7/16") bolt for the engine side. There's a solid sleeve between the outer washers of the soft elements. (Be sure to pay attention to which soft part goes where; they are not the same, front/back, and are reversed, top/bottom.)
 
The upper bolts are mostly in tension but there is some shear load.
The shear load is easily taken by the close fit of the 3/8" hole in the thick washer on the mount.
For the tension load, the over-sized diam. of the tubes on the mount has no influence.
The purpose of the space is to allow a bit of tolerance for the mount to change shape slightly while
welding and then not have to have the mount under a preload to make the holes align with the fuselage.
 
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Thanks for the responses, I still think a bushing is a easy thing to do, if only for my mental health and confidence.
 
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