Firewall "Pinning"- modifying ARF "gasser" firewalls to let standoffs work properly.

I have found through trial and error that proper securing of standoffs for gas engines on the Chinese ARFs can be a real challenge.  To improve reliability and longevity of the engine attachment to the firewall, I modify the firewalls by "pinning" around the standoff mounting bolt holes as follows.

BTW - What happens if you DON'T make this mode is simple..... the firewall crushes when you install the bolts/engine the first time.  Then, although tight, through running the engine, the firewall crushes JUST enough to let the bolt lose tension against it's lockwasher.  From vibration, the loctite starts failing on the threads, then the bolts loosen from the REAR of the firewall.  You can guess when you'll discover that "Somethin' just ain't RIGHT about this.... "   Probably during flight.  If you're LUCKY, you'll notice when starting the engine and watching the shake.  Of course, loose mounts will make all sorts of things go wrong in flight, so you'll notice pretty quickly....

It doesn't add much weight, if any, and takes a little time to do properly, but pays off .  Be sure to use a sharp drill, don't push the bit, and use a pretty high speed to minimize the splintering that WILL occur.  It may be best to hold a "back up" ply piece behind the firewall when drilling the holes from the front.

My mods have been as follows...
1. Obtain 3/4 or 7/8" flat washers (not the real thin fender washers, but perhaps 1/16" thick or so) at Lowes, Home Depot, Wal Mart, even.
2. After drilling the bolt holes through the firewall, drill at least six, preferably 8, 3/32" holes about 3/16 out from edge of drilled holes.
3. Carefully install hardwood dowel pieces (thicker, round toothpicks are perfect for this) using thick CA, or my favorite, the expanding polyurethane "Gorilla" glues. Don't stress about having them perfect length on the FRONT face, but be absolutely certain that they do NOT protrude beyond the REAR of the firewall.
4. After completely dry, use a dremel sanding drum, or cutoff wheel to finish the front face of the dowels flush with the firewall face. Very important to be flush, and smooth. Seal the firewall after.
5. Install the engine standoff bolts from the rear of the firewall using a split lockwasher, standard #10 flat washer, then a LARGE fender washer. On the FRONT of the firewall, be sure there is a large FLAT FENDER washer between the standoffs and the firewall when tightening.

This process ensures that you will not crush the somewhat flimsy light ply of ARF firewalls, and makes certain that you can adequately tighten the bolts/standoffs using just regular blue loctite and not worry about them loosening. This is really a fool-proof procedure, and I do it now on all airplanes with gassers.

                                     It ain't "pretty", but you get the idea (plus, you can CLEARLY see the indentations of the previous standoffs installed!!)