Pre-load tension on engine mount?

[ChiefPilot]

Now that my wings & gear weldments are installed, I decided to move onto the engine mount. Unfortunately, it's one challenge after another .

Of the six holes pre-drilled by Van's, I can only get four of them to match the engine mount i.e. I can only fit bolts through the 1/4" holes at corners of the engine mount. The middle two holes along the bottom are so far off I think I need to just replace the gussets and redrill.

My question is this - in order to get the four holes to match up enough to get the 1/4" bolts through the 3/8" holes in the engine mount, I need to flex the mount a bit. Not a whole lot, but the engine mount seems like something I don't want to pre-stress. Am I correct in this assumption, or is it ok to flex the engine/nose-gear mount enough to get the bolts in place?

Thanks!

 

[jsharkey]

In general you shouldn't flex anything......

Try opening up a couple of the diagonally opposite corner holes to the final bolt size and then mounting the frame using the final bolts. You can then open up the other four holes to the final size using the frame holes as guides. All six holes should then line up fine. I had to use a washer in a couple of places under the frame to level things up and prevent flexing the frame out of plane.
Jim Sharkey

 

[ChiefPilot]

Try opening up a couple of the diagonally opposite corner holes to the final bolt size and then mounting the frame using the final bolts. You can then open up the other four holes to the final size using the frame holes as guides. All six holes should then line up fine. I had to use a washer in a couple of places under the frame to level things up and prevent flexing the frame out of plane.
Jim Sharkey

Thanks - this got me sorta close, but only for the for corners and even then I needed to flex the mount a small bit. I spoke with Ken Scott @ Van's and he suggested that the only way I would put too much pre-stress on the mount was if I hitched up to a tractor . Anyway, with only very slight pressure it fits snugly against the four bolts at the corners.

The two lower middle holes are nowhere near close, however - with the four other bolts in place only about 1/3 of the 1/4" hole was visible though the 3/8" hole in the mount. After consulting with both Van's and my tech counselor, I drilled out the gussets and will make new ones to be match drilled to the mount.

Thanks!