I'm putting together a Lanier Citabria ARF and am getting ready to mount the engine to the firewall. The kit instruction manual says, "Align the mount and motor assembly on the centerlines of the firewall and mark the correct locations for the holes." Where are the "centerlines of the firewall"? The firewall has no marks on it at all. Does anybody know what they mean here?

Thanks,
Les

It's possible that the manufacturer of the ARF installed the firewall with the marks on the inside of the fuselage instead of the outside. Not really a big deal, but it does make it hard to find the lines.

Place the cowl on the fuselage without the engine installed. Sight through the prop exit of the cowl while looking at the firewall to find the approximate "cowl center" of the firewall. Now remove the cowl and set the engine on the firewall while holding the fuselage vertical. This will give you an approximate position for the engine location. It helps to find the engine center line and mark it somewhere on the engine. You can also make an engine backplate out of wood, mark the prop shaft center line on it with an "X" and place it on the firewall to help you find the "cowl center".

Go a step further and you can drill a small hole in the plate at center to make marks through. Further still and you can drill holes in the plate at the same location that you engine has them in.

The more accurate you can locate the "cowl center" the more accurate you will be in locating the final engine mounting position. With care and patience, you can find the exact location of the mounting center and install your engine without mounting the engine more than once.

I use various forms of clamps and such to hold the engine to the firewall when I use an engine to find center. I never, ever, cut on the cowl untill I am absolutely certain the the engine is mounted exactly where it needs to be. No holes are drilled in the firewall until the "cowl center" (mounting center) is located.

I use this mounting method on ALL the arfs' I set up. The firewall reference marks are usually only a good starting point. Bottom line is I want the engine centered in the cowl with the cowl installed on the aircraft where it's supposed to be.

Thanks. I really appreciate your response and I will follow your advice.

Les

I forgot a small item that may help out a little (just a little. You can add a dowel to the plywood plate that you made to match the engine backplate. Make SURE that the dowel is located exactly at the engines prop shaft center line and is dead straight with the plywood mock up.

If you have also drilled holes in the mock up back plate that correspond with the mounting holes of the engine back plate, you will have a complete package for your engine installation.

Center the dowel in the cowl, mark you mounting hole locations, and voila! Your done.