Engine mounts sagging

[kevinh]

> I have scale drawings of the rubber mounts if anyone wants to make their own molds.

Mike that sounds awesome. If you send me the drawings I might try my hand at 3d printing some molds then pouring in the goop. Hmm - I might just try printing TPU (shore 95a hardness) directly... Interesting!

[Rynoth]

Today I put my newly painted cowling back on the aircraft for the first time in 1.5 years. I then noticed that the prop hub was rubbing the cowling at the bottom of the opening in a way that I'd never experienced before. I then looked at the rubber engine mounts and found exactly what has been described in this thread.... the aft-lower engine mounts, on both sides, have begun to extrude over the engine mount. This is with the aircraft sitting in the hangar for 1.5-2 years since the engine was mounted (never flown.)

I'll post pictures soon.

[Dennis W.]

Mine held up while I was building......used larger washers behind bushings and didn't have the "squashing" over the engine mount......engine mounted about 3 years before I flew it. But when I flew it, dropped significantly within the first 3 hours of flying. Have replaced mounts 3 times since then and same issue....sags after about 1 to 2 hours flight time. Finally gave up after the third time....just monitored engine position relative to cowling to make sure its not rubbing or sagging further. However, have about 130 hrs flight time now and its sagging worse and need to do something. Was hopping folks at Sonex could offer some ideas but got nowhere. Not wasting my time putting the factory bushings on again.....too much work for same results.

[Rynoth]

As promised, pics of my sag after 1.5 to 2 years sitting in hangar.

1) My engine cowl was perfectly aligned with the prop hub when I finished it, this is how it appears now...

https://drive.google.com/open?id=0B4Apj ... EFKTTlQMjQ

https://drive.google.com/open?id=0B4Apj ... EFKTTlQMjQ

Lower left aft engine mount. It's pressing (extruding?) over the smaller diameter of the mount.

https://drive.google.com/open?id=0B4Apj ... VVZTEl1WHc

https://drive.google.com/open?id=0B4Apj ... zdHLS1sZGc

https://drive.google.com/open?id=0B4Apj ... 1ZFX081ZWs

Lower left aft side:

https://drive.google.com/open?id=0B4Apj ... VFiWHM4YW8

Edit: Fixed the image links

[Bryan Cotton]

Ryan,
I can't see the pictures.

[Brett]

It's like the bushes need to be twice the size or something and have a larger surface area on the mounting accessories plate. My lower ones now after the third set and 50 hours are about half the original size with washers stuffed behind them. I'm at the point again where I need to do something as the vibration becomes unpleasant. Flying with new bushes is great for about 4-5 hours then it slowly starts to vibrate more and more as the bushes squash up and harden.

[mike.smith]

As promised, pics of my sag after 1.5 to 2 years sitting in hangar.

1) My engine cowl was perfectly aligned with the prop hub when I finished it, this is how it appears now...

https://drive.google.com/open?id=0B4Apj ... 1ZFX081ZWs

My first suggestion is you add 1 or 2 fender washers between the back of the rubber bushing and the engine mount. They need to be at least the same diameter as the rubber, and preferably a bit larger. That will at least keep the rubber from squishing out around the engine mount.

But that's just a temporary help. The overall issue of the sag is still an issue. If anyone wants to experiment with engine mount braces, or new rubber mounts, let us know how it goes!

[sonex1374]

Ryan,

A side comment came to mind viewing one of your pics. Zip ties are very harsh on soft rubber items like your ignition wires, especially if the edge of the zip tie presses in at all. The single zip tie securing both wires is guaranteed to chafe them in only a matter of hours. Better to use some rescue tape to create a cushion around the wires and protect them from the zip tie, or use two zip ties to get them to each lie flat on their respective wires.

Jeff

[Rynoth]

Ryan,

A side comment came to mind viewing one of your pics. Zip ties are very harsh on soft rubber items like your ignition wires, especially if the edge of the zip tie presses in at all. The single zip tie securing both wires is guaranteed to chafe them in only a matter of hours. Better to use some rescue tape to create a cushion around the wires and protect them from the zip tie, or use two zip ties to get them to each lie flat on their respective wires.

Jeff

Jeff, that's great advice, thanks! Going to get my hands on some silicon tape.

[kevinh]

Re: quick ties
I copied a great trick on my previous plane and it held up for at least seven years before needing replacement (and no chafing). I don't have a pict but if you cut a short length of 1/4"ish fuel hose (about 1/4" long) you can shape the quick tie as a figure eight with one end of the 'eight' over the tube and the other end over the wire bundle, with the fuel hose serving as a standoff. It makes for a nice easy install - doesn't last as long as adel clamps, but easier.