I have a Senior Telemaster which has the firewall drilled for a different engine mount than what I will use. I am thinking about using 4 1/4 blind nuts and screws, mounted in the corners to hold an additional firewall in front of the existing one. I will then mount my engine mount to that one to facilitate changing engines and mounts easily. Will this cause any type of problem? It will be nice to be able to use it as a platform for checking out various engines. It has a chunk of steel for nose weight, so if I remove it I don't think the additional weight will cause any trouble.

Four, I have a lot of engines and only a few planes so I change engines a lot. If the back side of the firewall is readily accessable I place masking tape over the front and fill the hole from the inside with epoxy, with the fuse standing on end. If I'm a litle about the strength I laminate some 1/16 inch ply over the inside or out side also. The method you're describing looks pretty heavy.

I agree it will be heavy, but I figure I can cut down on the weight in the tank compartment. I figure it will be easier to take out the plywood, change the engine mount and stick it back in without having to mess with the actual firewall.

Does the firewall on the S/T Kit already have the thrust angle built in?

fourStroker, your idea looks good, especially since you need the weight there anyway. I'd say go ahead, will work fine.