engine mount cups?

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13brv3

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Greetings,

I'm going to be welding a mount for a 912 (using the Rotax ring mount) for my Sonex Onex, and it would be nice to find pre-fab cups (not sure that's the right term) that are ready to weld. I believe it might be possible to find them for the heavier dynafocal mounts you see on larger Lycomings, but I'm thinking those mounts would likely be overkill for a 912?

Rotax has rubber mounts, but they're stupidly high priced, and I haven't even found dimensions for them, much less cups.

My initial plan was to use C-90 rubber bushings, and steel mounts similar to the way the Legal Eagle makes them. Knowing how rough the 912 can be on startup, I'm not sure if those would have enough flex.

Any suggestions?

Thanks,
Rusty
 
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TFF

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912 mounts are pretty large compared to a C90. That are almost Lycoming size. 80% about. They look like baby bed mount isolators you see on a Continental 550.
 

Dan Thomas

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The Continental O-200 shockmounts are smaller and less flexible than the Dynafocal, but the engine is smaller than anything that uses the Dynafocal, too. The O-200 shockmounts are much more flexible than the C90 conical rubbers. The shockmount "cups" are machined into the engine crankcase but are simple and would be easy to machine from steel bar stock.

1612638178732.png

The "cup" is shown here in a picture from someone that makes aluminum adapters top mount the O-200 using the C90 rubbers:

1612638253877.png

The flanges of the inboard steel shockmount cups fit into the machined recess in the crankcase lug "cup."

1612638344146.png
 

13brv3

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I've seen those adapters from O-200 to C-XX and maybe earlier O-200. The larger shockmounts do look interesting, but I haven't found them for sale anywhere. After a bit more research, it appears that people want to switch from the larger mounts to the smaller cone mounts for various reasons.

The conical rubber PN- 22387 is said to work for O-200 and smaller engines, and that's what I've been planning to use. I've already fabricated the "cups" based on some drawings I found for the Legal Eagle. I'd weld the mount tubes to those cups, and bolt the Rotax ring mount to the conical rubber. I think it should be adequate, but I'm just doing some second guessing before actually starting to cut tubes.

Rusty
 
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TFF

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I would contact Lockwood. I think they have cheap homebuilt mounts as well
As the expensive certified ones.
 

karmarepair

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I would contact Lockwood. I think they have cheap homebuilt mounts as well
As the expensive certified ones.
What Lockwood has: Barry (a brand name) Mounts in various hardness. Engine & Muffler Mounts - Accessories
I think these are best loaded in shear. The isolated mass is bolted through the center bushing. The "neck" in the middle of the mount (which is in two pieces) fits tightly into a bushing that anchors to the airplane. See http://blogs.solidworks.com/tech/wp-content/uploads/sites/4/2018-09-11_11-51-37.png for an example of how this sort of mount works. Stiff "Snubbing" washers compressively pre-load the rubber, and keep it from squozing out.

There is another type of mount that does NOT require "cups". Picture two bolts with their heads embedded in a rubber biscuit. That's the type I'l be using on my V-Twin tests, 'cause that's what generator set OEMs use with this engine in their application. Everything rotating and vibrating lives on a "raft" that then gets mounted to the "chassis" via these Rubber Biscuits <sarcasm, gratuitous Blues Brothers reference>.
 

13brv3

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I've used those Barry mounts on a Hirth application previously, and I like them. Funny thing is that I've had the data sheet open all morning wondering if I could come up with a good way to use them. I especially like that there are multiple hardnesses to use as needed.

The ring mount only has bolt holes, and the Barry's mount could bolt directly through those. I'd have to come up with a plate to weld to the mount. A thick steel plate would be heavy, but maybe a thick aluminum plate bolted to a thinner steel plate would work. I'll do some more scribbling today and think about this some more.

Thanks,
Rusty
 

13brv3

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FWIW, I've decided to go with the larger conical mounts made for Lycomings. I'm going to make my own cups, which shouldn't be too difficult. I'll machine aluminum inserts that can be modified as needed to allow at least some variation in mounts if needed. Thanks.
 

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