Engine: Verner 3VLA

[Chuck in Indiana]

I wish I had one of those benders, so I can't tell you what it will do. My engine mount holes were some weird metric size between 5/16" and 3/8". I reamed it out to 3/8 to use AN hardware. You want the bolts to fit the case pretty well.

[Brock]

I wish I had one of those benders, so I can't tell you what it will do. My engine mount holes were some weird metric size between 5/16" and 3/8". I reamed it out to 3/8 to use AN hardware. You want the bolts to fit the case pretty well.

On the 3VLA the bolts don't fit the case but the mounts.  The wrong mount that was sent to me was setup for 3/8" bolts.  I think that is what my 200 HP lycoming takes while the 85 hp on the sonex uses 1/4" bolts.  I was wondering if 3/8 was just overkill and if 5/16" would provide enough of margin.  Bigger bolts = more weight.

[Chuck in Indiana]

Oh, I'm sure the 5/16" are plenty, but I didn't want that less than turbine smooth Verner wallering out (Indiana term)  those holes in the case if the bolts don't fit well. At least that was my reason for reaming to 3/8".
Now.. your engine is completely different with the rubber directly against the case.. and I'll bet you have enough experience to make the call.

[Brock]

Today I started on the engine mount.  It's been long in coming since I was still working on the firewall engine bolt mounts.  Alittle aobut that.  I decided (sorry no pics at this time) to weld the engine mount bolt bushing directly to the tubing like I saw on a friend's Citabria.  What I didn't count on was gobs of filler needed to properly weld them into place securely.  I would have saved on time and frustation (aka learning opportunities) if I had welded in the corners plates, drilled them and then weld in the bushings.  Anyway, it's done.

So for the first engine mount task is to build parts. There will be four bushings for the firewall side as well as four for the engine side.  Then in the middle will be this ring pictured below.  It was pleasing as to how well it turned out, almost like I've done this before, Not.  The OD of my firewall is 14 1/8 square.  I decided to match that with a 14" hoop.  I thought a long time what tubing to use for the hoop.  In the end I decided to try out the light 5/8" x .035 because I had a long piece and I already had the 5/8" dies for the HF tubing bender.  The reasoning is that the two tubes coming off each corner of the firewall will basically meet with the tubes coming from the engine, thus the hoop becomes more of a stabilizer than massive structural provider.  What do you think?

There is a technique to getting the hoop to bend with out a twist.  I caught on right away that the tube needs to be coaxed as the bend progresses.  The ends finished just one diameter off which was needed to manuver and to then remove the hoop.

After bending I cut both ends off at the same time with a hacksaw which gave them both the exact same angle, that was a very nice surprise.  Next I drilled a small hole necst to each end (should have made the holes closer to the ends than I did) and installed an interior sleeve for alignment, strength, and weldability.  Turned out nice.

Finally I couldn't reist holding the hoop up in front of the (upside down) firewall.

[Chuck in Indiana]

That is freakin awesome. Attaboy X 2.

[Brock]

The size of the hoop in that last picture has bothered me and I just figured out why.  The hoop which is slighly smaller than the firewall looks too big.  But looking at the pictue I notice the taper of the tubes aft of the firewall and realize that the hoop would look better (best?) if that taper was caried forward to the hoop location.  Thus the hoop would need to be about another inch smaller.  Oh well,  It's not going to get unwelded and resized.

[Dan_]

May not be noticeable when that big beautiful engine gets mounted to it.

[Brock]

A bit more Progress on the Engine mount.  I clamped this 3/4" playwood to the airframe and through drilled the corner holes to make a base to jig up the mount.  I'll only very lightly tack a few tubes then remount it to the airframe in case things don't line up perfectly.

I'm doing some head scratching and am wondering if there are any engineer types out there to give input.  So, the hoop is 5/8" x .032.  A little on the light side but I'm guessing it might work with the right bracing.  After mounting the bolt-bushings and hoop to the jig I realized that my bolt-bushings are only 1/2", and while plenty strong for the task, it will be hard to weld a 5/8" brace to.  Three options, use the 1/2" x .052 tubing I have on hand for the braceing (see the blue tape for how I'm thinking of bracing), or use 5/8" x .032 and flatten it a bit, or change the bolt-bushing to 5/8 x 5/16 (bore) which would be over kill.

[Chuck in Indiana]

The .035 tubing has been fine on everything on Bullet. Once you start coping the bracing, you'll see that it's no problem to weld the bushing to the tubing and BA (big ass) washer. 

[Brock]

The .035 tubing has been fine on everything on Bullet. Once you start coping the bracing, you'll see that it's no problem to weld the bushing to the tubing and BA (big ass) washer. 

Thanks Chuck for the reply & information/expirence, it helps.  On the BA-Washer, I don't see it's purpose and was not going to weld them on.  They are present on my jig to keep the bolt-bushings perpendicular to the flat plywood and at the same level.  They would make welding a bit easier, is that their function?

[Chuck in Indiana]

Actually they spread the load to keep the bushing from trying to drill a hole in the firewall.    Check out factory mounts.. they all have them.

[Brock]

Kinda like a 3D puzzle but one you have to also make up the pieces as you solve it.

I finally relented and replaced the 1/2 bolt-bushing with 5/8" as it made more sense for welding the 5/8" tubing.  Also the engine side will get 3/8" bolts as that is what the shock-mounts are designed for.  Now I wish I had gone with 5/8"x3/8"(bolts) all around.  To late on the airframe as the bolt-bushings are only 1/2" and I'm not about to grind them out to reinstall.  Well not yet anyway.  Anyone else dislike doing a job twice?

The jury has yet decided if the washers are going to get welded or will remain part of the jig.

[Chuck in Indiana]

Let me make that decision for you.If you don't use them, with vibration the bushings will fret the aluminum crankcase which will lessen the torque on the bolts  which will fret the case some more and waller out (technical term)    the bolt holes, etc. The same will happen to the firewall to a much lesser degree. I'd make the washers out of 4130 to boot.