Engine mount bushings - improper installation.

[Bryan Cotton]

So I was inspecting under the cowl after completing other maintenance, and found this:


Initially I thought my poly bushings were toast. I took one out and it was pristine. I had a new set to compare to. Then I realized that the reason Sonex uses commercial washers is to allow them to slip over the engine mount tube where the bolt goes through. So I had tightened my stack of AN4 fender washers up against the tube and had not compressed the bushings. Whoops. I'm sharing this mistake in hopes it may help somebody else.

[sonex892.]

Wow! That engine must have been running ultra smooth Bryan.

[Bryan Cotton]

Wow! That engine must have been running ultra smooth Bryan.

Smooth except at low idle. Had no idea until I spotted it. 71.5 flight hours to date.

[Area 51%]

Has the adapter plate been resting on the mount tubes? I helped a Xenos driver replace his sagging rubbers and found the plate had rubbed a nice groove in the mount tubes.
After seeing that, I installed a sacrificial aluminum sleeve over the tubes on my mount.

[Bryan Cotton]

Has the adapter plate been resting on the mount tubes? I helped a Xenos driver replace his sagging rubbers and found the plate had rubbed a nice groove in the mount tubes.
After seeing that, I installed a sacrificial aluminum sleeve over the tubes on my mount.

It had not been resting on the tubes.

[Bryan Cotton]

So my alignment with the cowl is off and I need to pull the engine off to distribute bushings. I'd really like to avoid pulling off the baffles. I'm considering a 3 point sling - around the two intakes and the prop shaft. Any experience or thoughts?

[Bryan Cotton]

So my alignment with the cowl is off and I need to pull the engine off to distribute bushings. I'd really like to avoid pulling off the baffles. I'm considering a 3 point sling - around the two intakes and the prop shaft. Any experience or thoughts?

Disregard - I pulled off the top to my oil cooler baffle and I'm using that lift boss.

[Bryan Cotton]

Has the adapter plate been resting on the mount tubes? I helped a Xenos driver replace his sagging rubbers and found the plate had rubbed a nice groove in the mount tubes.
After seeing that, I installed a sacrificial aluminum sleeve over the tubes on my mount.

It had not been resting on the tubes.

Update: there was some contact on the bottom tubes. Glad I caught this now.

[n502pd]

Absolutely, the large bore washers are used to be able to slip over the mount tubes, and the front small bore washer is meant to bottom against the same mount tube, and make the resulting compression of the rubber bushing to be pretty tight, and fill the cavity in the aluminum plate. Great catch, and good video!

As my total time is pretty much the same as yours, 71.8, my mounts were saging some. Fount\d three of the four bottom bushings were just about ready to allow steel on aluminum interfacing, so I caught mine in time. replaced with sonex bushings. reused a couple of top bushings that were not damaged.

Lasty, has anyone, over the recent years, found other bushings of same design parameters, but made of more longer living material? there was some discussion a number of years ago, but today I am not sure if any good results were discussed.

Any info and/or comments?

[Bryan Cotton]

Mine was just a screwup - the super pro bushings were not compressed at all. Now I have about 20 hours on them with proper installation and there is a little sag. I would recommend having the engine tipped up just a little bit when you do a fresh installation.