The Murphy Builders Site

Thanks for your help so far with my engine mount design. I have decided to go with 1" x 0.065 wall thickness tubing. The cost increase and additional weight for a bit thicker wall was negligible. I am also going with that size throughout the design instead of some members being smaller for the same reason. I am going to use a "swing-out" mount design that starts at the firewall with a rectangluar block of metal with a hole drilled and tapped for a bolt through the firewall, and then there will be a vertical bolt through a c-section welded onto the end of the first section of 1 inch tubing that will fit over the block attached to the firewall. This will allow me to pull two bolts on one side and swing the entire mount with the engine supported by a hoist to give me better access to the back of the engine.

At each of the four points that the mount will attach to the engine, a rubber shock will be used with bolts oriented vertically because I don't want the bolts to be stressed in shear.

I would like to use some industrial "biscuits" for shock mounts. There are lots of different sizes and shapes available. Unfortunately, there are also different types of rubber with various hardness/softness characteristics available as well. I wonder if anyone on the list can answer the question about what hardness/softness should be used for an engine mount.

Mike Kimball
044SR




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Mike

Can't help you with the rubber other than to mention that one can custom
cast urethane to pretty much whatever hardness you like. Flexane 80 and
the hardness modifier in the appropriate mixture is supposed to be easy
to use. I eventually used Lycoming conical mount rubbers on my little
Subaru but softer with more available movement would have been better
especially since mine are located quite far apart.

Like rivets, bolts are excellant for resisting shear. Unlike rivets they
do well in tension as well such as cylinder head bolts. They don't do
particularly well when cantilevered such as on conical engine mounts as
they must be very large (and heavy) to resist bending. I suspect that is
what you are referring to. Bolts used as pins where the bolt goes
through 3 holes are strong efficient fasterners per unit weight. Like a
small door hinge pin or the wing mount bolts. Sometimes that is referred
to as double shear I believe.

Ken

Mike Kimball wrote:

Thanks for your help so far with my engine mount design. I have decided to go with 1" x 0.065 wall thickness tubing. The cost increase and additional weight for a bit thicker wall was negligible. I am also going with that size throughout the design instead of some members being smaller for the same reason. I am going to use a "swing-out" mount design that starts at the firewall with a rectangluar block of metal with a hole drilled and tapped for a bolt through the firewall, and then there will be a vertical bolt through a c-section welded onto the end of the first section of 1 inch tubing that will fit over the block attached to the firewall. This will allow me to pull two bolts on one side and swing the entire mount with the engine supported by a hoist to give me better access to the back of the engine.

At each of the four points that the mount will attach to the engine, a rubber shock will be used with bolts oriented vertically because I don't want the bolts to be stressed in shear.

I would like to use some industrial "biscuits" for shock mounts. There are lots of different sizes and shapes available. Unfortunately, there are also different types of rubber with various hardness/softness characteristics available as well. I wonder if anyone on the list can answer the question about what hardness/softness should be used for an engine mount.

Mike Kimball
044SR

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