What material are you using for mounting Homelite engines ? I used 3/8" plywood for a firewall on a SPAD Spadet with a 52 four stroke on it.Would I need thicker for the Homelite 30cc and would it be plywood or does anyone use the material from the plastic looking cutting boards,like at WalMart ? Have to start gathering up materials to build a plane for my engine.

The 3/8" ply is good enough

There are many types pf plywood. Utility grade, construction grade, lite ply, marine grade, aircraft grade. Different cores, different glues, different number of plies. Different applications. And, of course different prices.

Softer FW materials will compress and allow loosening of the attaching hardware, necessitating checking and re-tightening.

I use aircraft grade which is usually birch faced with no internal voids, and with strong waterproof glues. All securing is with long set epoxy and cross screws or dowels, coupled with triangular stock and doubling of the fuselage as required.

Of course, I think too much about it.

Works for my applications; good luck with yours.

Thanks guys.I have a piece of 3/8" aircraft grade here,but wanted to check if I needed heavier than that.

There is a lot of difference in ply. For instance, I've found everything from 5 ply birch to pine, balsa, pine, 3 ply in 1/8" thick ply. I use 1/8" in a lot of my planes for mounting my 46 size engines right to the lugs or double it up for firewalls. After I've drilled the holes for mounts or engine lugs I always wick in some thin CA in the hole and both sides to fill some air space in the wood grain. This makes the wood denser and less likely to crush when tightening nuts, bolts or blind-nuts.