engine shock mount SDR

[mshac]

This thread would be SO much more effective if it had PHOTOS!

Most of owners don't know the ins and outs of Lord mounts, halves, spacers, etc. because we've never dealt with them. If this issue is serious, please DOCUMENT it with photos, and copies of your emails with the Lord engineers. Thank you!

[wslade2]

Yes, photo helpful; have not ignored your post but carefully followed the wording to be sure I understand. I'm straining my memory banks. I did mounts a couple years ago. I'm pretty sure they were Lord mounts. And difficult to find a complete set. Getting them in was a wrestle. Seems like they bottomed out (as you're describing), everything looked ok and rubber was snug, so I called it a day there. Will look next time I am out at airplane and review manual too.

Are you saying once everything is tightened the rubber And the mount isn't snug? There's play?

[SteveG]

Hopefully these photos illustrates the issue graphically. The mount halves are designed to meet using a 0.620" spacer between them but my (our?) spacers are 0.770" thick leaving a 0.150" gap that cannot be made up. This issue also translates to the internal spacer which defines the amount of compression preload. Its length is designed to permit 0.410" of compression but because the mount halves never meet one would have to compress the mount 0.560" to tighten, a distance that cannot be realized with the length of threads available and is 37% greater than intended. As is, the mount never becomes a unified, stressed assembly as designed. The engine is just hanging off the upper mount half.

The thickness of the engine mount spacer, not including the flange which extends through the mounting plate, is compatible with the 0.310" flange of the two shock mount halves. I'm beginning to believe that the part was never designed correctly by Cessna and that this issue has existed from birth. Hard to fathom but I have no other explanation.

[mshac]

Thank you for the photos. What if the spacer were milled down .150?

[Kim Geyer]

I’ve changed many Skymaster engines over the years and I know they can be a pain.
Get your parts book and make sure your hardware is correct for each corner. The p/n for the mount is correct and they don’t touch each other in the middle of the mount.

[SteveG]

I briefly considered altering the engine mount spacer but that would change the entire dynafocal geometry. Wasn't willing to go there. A work-around that I do believe has merit is to add a spacer to close the gap between shock mount halves and to add a like length to the internal spacer through the use of standard flat washers. This is obviously an "extrajudicial" solution and therefore "experimental". See attached photos.

Although I respect the considerable experience Kim has with these aircraft I do not understand his comments. The exact mounting hardware used is not relevant to this discussion. And his contention that the shock mount halves do not meet in the middle is just a restatement of exactly the problem, they are supposed to meet. Their meeting is necessary to carry the load across the entire cross-section of the mount and into the lower mount half and even more importantly the length of the internal spacer is predicated on that relationship. As is the internal spacer is just rattling about doing nothing.

[Kim Geyer]

If you have a parts manual use the hardware stack as show if the nut bottoms out on the bolt before the mount halves have contacted the internal space then add a washer under the nut and again the mount halves do not contact each other inside the mount if they do the mounts will be able to move inside the engine mount frame and that’s not good.
I’ve done 24 in the last few years. I do know how they go
I don’t mean to be snarky, I want to make sure you get it right