Now that we have the center of the firewall marked it's time to mark where our motor mounts go. There is no set “exact” place where it will go because it will be different depending on the engine that you will use on this plane. Place your motor on the firewall so that it's centered on the centerline that we drew in the previous step. Take your time and get it as accurate as you can (picture #1). Once you have the engine centered on the firewall use a square to mark where the motor will sit on motor mount once it's installed (picture #2), make this mark on both sides of the motor. Use a ruler to extend this mark up the firewall so that it is drawn past the mount hole that are in the firewall (picture #3). Picture #4 shows the parts that we need.

For the next step in this I want to go back to something that I said at the start of this build. Measure twice, cut once. We may not be cutting, but this is definitely something that was want to make sure is marked and measured correctly. Trust me when I say that I have learned the hard way when I started building planes. Mis-marking where the motor mounts can be a royal pain in the butt. With that in mind we're going to double check our marks. We could use a ruler and try to see if the marks are correct, but I prefer to actually check this with the motor in place. If you look at picture #5 you can see that I have put the motor mounts in place, but instead of installing the blind nuts with the barbs set in the wood I've turned them around backwards (you could also use nuts to do the same thing). What this does is let us put everything in place and check our measurements before we drive the barbs into the wood. Put the motor mounts on the marks that we previously made and snug down the nuts on the back of the firewall (picture #6). Set the motor on the mounts and check for its fit on the mounts (picture #7 and #8). You will want the engine to sit as close to the mounts as possible, but you don't want to spread the mounts apart when you put the motor in place (picture #9). This will cause strain on the mounts when the engine is running and will eventually cause a failure of the mount. When you are happy with the way the engine sits on the mounts it's time to check our measurements. Check to ensure that the mounts do actually sit centered on the firewall. You should have the same distance from the centerline to the motor mounts on both mounts. If the measurements aren't the same, take the time and correct that now. Once you are happy that the mounts are in the proper place it's time to set the blind nuts in place, but before you do make sure you mark the location of the mounts just in case you slip while you are installing the blind nuts. To make sure that the mount position doesn't change while you install the blind nuts we need to install one at a time. Picture #10 shows us removing one blind nut and turning it upside down so that the barbs are set in the wood. Since we don't want to move the mounts we won't be using a hammer to set the blind nut like we did earlier. Instead, after you turn the nut over use a screwdriver to tighten the screw on the front of the firewall. This will pull the blind nut into to the wood. Now continue on to the rest of the blind nuts until you have all four set (picture #11), make sure you keep checking to make sure that the mounts stay in place. After you have all four nuts in place, we'll use 5-minute epoxy to set the nuts in place like we did with the Front Gear Bearing mount earlier.

Pictures
1. Center the engine on the centerline of the firewall.
2. Transfer the location of the engine mounting lugs to the firewall.
3. Extend the mark on the firewall.
4. All the parts needed to mount the engine.
5. Install the blind nuts “backwards” so we can check our measurements.
6. Make sure the mounts are on the marks that we made.
7. Place the motor on the mount and check for it's fit on the motor mounts.
8. Checking the motor fit on the mounts.
9. Make sure that the motor doesn't spread the mount apart.
10. Turn the blind nuts over to install them into the firewall.
11. All four blind nuts installed.
12. Use 5-minute epoxy to set the blind nuts in place.



Until next time

Ken