I'm trying to figure out the best way to repower my Kadet Sr ARF. I want to mount a OS 52 Surpass 90 degrees to vertical and I have some questions. First, Can I epoxy a piece of 1/2" play onto the firewall and then put the engine mounts on this. The clearance will not be a problem but will it be secure enough? Should I also screw this mounting block to the old blind nuts in the firewall and what is the most acceptable method for securing the mounts to the block, wood screws or should I put blind nuts in the mounting blocks before I epoxy it onto the firewall.
Thanks in advance

You can't trust wood screws to hold your engine securely. I would use bolts and blindnuts all the way through your spacer block and the old firewall. That's the only way to be sure the whole vibrating mass will stay together long. Believe me, having an engine come loose in flight is no fun.[]

Unless the existing firewall is damaged in some way, I wouldn't worry about adding the plywood in addition to the firewall, you can just redrill to match the mounting pattern of the mount turned 90 degrees. The stock firewall is plenty strong for that motor. If you need the engine to be further forward to clear the cowling, then all you have to do is mount the engine further forward on the mount, or use a slightly larger mount.

I agree with Tbird on not using wood screws, use bolts(with lock washers) and blind nuts, and/or self locking nuts if necessary due to engine vibrations.

Thanks for the replies,
but.... The reason I was asking about adding the plywood mounting block was to avoid having to put new blind nuts through the firewall. That would mean removing the fuel tank to gain access to the back side of the firewall. Otherwise it is completely inaccessable. I can screw the mounting blocks to the firewall using the old blind nuts and I can put blind nuts in the mounting block before I install it on the firewall. I guess my question is should I screw the new mounting block to the firewall using the old mounting location and blind nuts or would epoxy be strong enough.
thanks

I'd use screws and epoxy. Epoxy alone might be strong enough but you will have no doubts if you use both. Since you're planning to use thick plywood you can countersink the screws that go into the old blind nuts and use pan head screws like the ones on this page to assure no interference:
http://www.microfasteners.com/catalo...ts/MSCMSPP.cfm
Most hardware stores should carry these and sell them individually versus buying a box of 100. Around my area you can get them at Home Depot, Lowes, Handyman Hardware. I'm sure there are lots of other sources in the area but these are all within a few miles of my house.