engine mount

[gill]

in need of a motor mount or drawing so i can build one.project is a bush caddy 164 w/ lycoming io-390 engine if anybody have one or knows who has one or even a drawing or measurments to build one let me know.THANX

[gill]

what is the size & thickness of 3140 tubing to use for a engine mount for a dynofocal ring on a lycoming io-390 engine ?

[crusty old aviator]

Tubing size depends a lot on the geometry of the mount. Mounts for a 200+ HP, 300+ pound engine usually use 1" x .058 (or .049) wall, 4130N tube. Don't forget to stress relieve all your welds...

[orange4sky]

I'm building an O-540 Super Stinson and designing the engine mount.

The Stinson fuselage, where it mates to the engine mounts, is made of arc welded 5/8 .035 at the top mounts and 3/4 .035 at the bottom which seems light but there are a ton of even heavier O-470 (+100lbs over Franklin) conversions around that are still hanging off those little straws.

I want to know if I should be scaling my mount tubes to the airframe (3/4".035) or going beefier. I'm not wanting to add unnecessary weight as the O-540 is about 65 lbs heavier than the Franklin.

Also, what is the purpose of the ear mount "ring" (more like a square on a dynafocal mount for an o-540)? Why not just terminate the tubes at the mounts

If mounts have to be so beefy, how have all those 470 conversions survived all these years?

[Kyle Boatright]

Also, what is the purpose of the ear mount "ring" (more like a square on a dynafocal mount for an o-540)? Why not just terminate the tubes at the mounts

You can buy the dynofocal ring from places like Aircraft Spruce. Then, you can align the ring the way you want with the airframe to set your thrust line, CG, and prop position and fab the rest of the mount around it. That will give you a self-braced hard mounting point for the engine. You want to bolt that heavy, powerful engine to something solid, not a noodle. Otherwise, that engine's gonna move a lot more than you expect.

As far as the tubing thickness goes for the balance of the mount? Dunno. Sorry.