Motor Mount

[Phil]

Like a few others, I discovered that my motor mount doesn't line up perfectly with the undersized guide holes in the fuselage. It's not bad, but probably a 1/8 - 1/4".

I can pull the mount into alignment with the holes by hand. But is it acceptable to pre-load an engine mount like that while mounting it to the structure?

Thanks,
Phil

 

[aerhed]

It is just a bunch of steel tubing after all. Don't know what everyone else will say, but I would probably over bend a little until it lined up with no stress. If it was a tube fuselage you'd just stick your knee in it and bend until you were happy. I suppose if you had to bend it substantially, you'd want to inspect for cracking and maybe stress relieve (torch), which would be hard on your powder-coat.

 

[rv10soon]

ENGINE MOUNT MISALIGNMENT

I am mounting my engine (older IO-540 D4A5) and have it mounted on the lower ears just fine, but the upper ears are too high and wide by about .25 to .3 inches. This looks like too much to try to bend the mounting frame. Any suggestions?

RV10-Soon
832-640-6284

 

[cholladay]

Mine was not perfiectly aligned with the fusalage either. After I mounted two holes I just drilled the others with the mount as a guide and they straightened up. I think Vans should just start drilling one hole in one of the upper corners and leave the others for us to drill.

 

[aerhed]

I am mounting my engine (older IO-540 D4A5) and have it mounted on the lower ears just fine, but the upper ears are too high and wide by about .25 to .3 inches. This looks like too much to try to bend the mounting frame. Any suggestions?

I think a little bending to match the firewall is okay, but If your dynafocal mounts are truly off, you're not gonna be able to bend that. Do a search here about engine mounting. Because of the focal angles of the mounts it may seem to be off, but isn't really. They only line up when actually pulled in & seated. Usually the engine side (forward end) of the mount is dead on. If it is truly off size, I'd call Vans about an exchange, but first try this: Hang engine on your crane. Install lower mount bolts medium snug. Lift engine to pull into top ears. Sometimes you will have to start the top bolts with the lord donuts loose & out of position. they will pull into place as you lift the engine & tighten the bolts. Sometimes you even have to bump the top donuts into place with a "persuasion tool" as you tighten. I hope this helps you.

 

[Phil]

They're all that far off, so an exchange isn't going to help. I've talked to 8 different builders and all have reported exactly the same problem. I'm just going to pull mine out to match the second upper hole and drill it.

In the process I discovered a second problem. The mount doesn't sit flush against the firewall. The mount is actually pretty flat; but the QB firewall isn't. This was causing a gap of slightly more than 1/4".

Their answer was to shim it so it's within 1/16" and bolt it down. They said since the engine sits on rubber mounts it's not an exact science.

Phil

 

[flion]

For what it is worth, when I replaced the engine mount on my -6A, I was worried about matching the holes drilled from the previous one (didn't need to worry as I had a later mount to begin with and the new one was off the same jig and fit perfectly). When talking the problem over with local fliers, one of them, an A&P, said that with spam cans if the mount was correct within half a mounting hole diameter it was considered good and forcing it to fit was acceptable. That's anecdotal and now I'm not sure if I needlessly worried or if I should worry about flying in spam cans.

 

[rleffler]

They're all that far off, so an exchange isn't going to help. I've talked to 8 different builders and all have reported exactly the same problem. I'm just going to pull mine out to match the second upper hole and drill it.

Phil,

This thread was starting to get me worried since I was going to install the motor mount today. It appears that I'm the anomaly. All my holes lined up just fine.

My issue was installing the two bolts by the firewall by myself. I had to get a little creative since my arms couldn't reach each side of the bolt in that location.

bob

 

[Phil]

Hey Bob,

Glad it worked out. If you think about it, I'm curious to know what the distance is between your holes. If you get a chance to measure them (on center) let me know. I think I'm about 3/8" too wide.

Phil

 

[rleffler]

Hey Bob,

Glad it worked out. If you think about it, I'm curious to know what the distance is between your holes. If you get a chance to measure them (on center) let me know. I think I'm about 3/8" too wide.

Phil

Sorry for the delay, it took me a few trips to the hangar to remember to write down the measurements.

Top bolts - 40.25"
Bottom outside bolts - 36"
Bottom outside to bottom inside bolts - 13 5/8"
Between both bottom inside bolts - 9"

Now that I have these written down and I'm at home, I see that the math doesn't add up. I didn't validate that the inside bolts on the bottom were in the same line when I measured between the outside bolts.

 

[Phil]

I finally drilled mine yesterday. Through the use of clamps and a spare set of hands we finally got it drilled. It does have some pre-load on it (it had to have it) but I think we minimized it as much as we could.

Phil