ORIGINAL: ameyam
Once the finger tightening is done, I use a spanner to tighten further. Normally you would tighten till it wont turn any further But, even with a little tightening, the top surface of the mount begins to sink under the pressure of the washer and the sides begin to bulge out. I have highlighted this with the yellow circle in the attached image. All four nuts have this problem and I have tightened as far as they go (or as far as I dare to). The problem is that this resin-FRP mount is very soft which is good, as it absorbs some vibration. It sits flat agains the firewall as well
Ameyam,
Such soft and flexible engine mount, any thrust angle that you trim will change in flight under the forces of the propeller.
So don't worry too much about the correct angles.
You don't need so many nuts there.
In order to avoid the compression of the mount and eventual failure of one bolt due to fatigue, you will need to make two thick pieces of aluminum, just like the base of the crankcase.
Similar oversized washers (aluminum or steel) should be added under the bolts that are holding the mount to the firewall, or similar fatigue failure may happen.
Bolts holding vibrating loads MUST BE tight; otherwise they will break off.
Best advice: install a harder engine mount.
If vibration absorbtion is desired, use one designed for that.