As I said in an earlier post, I had planned on getting some work done in here but I decided to spend the time with my family. I know that it sounds like I'm climbing on my soapbox, but urge everybody out there to make sure that you take care of your family before you take care of the hobby. To me nothing is more important than my family. We spent a good portion of the weekend together as a family, and the funnest part was putting up our Christmas lights on our house. We love doing that, and we tend to “over-do” it too. How much? Have you ever seen National Lampoon's Christmas Vacation? Remember when Chevy Chase plugged in the lights and killed the power for half the town? You're getting close!! . When we turned out lights on we got a call from the control tower at the local airport and they informed us that we were blinding the pilots as they came in on final approach!! [X(]

Anyway, back to the build. In our last post we had epoxied in the blind nuts for the motor mounts. Our next step will be to locate the motor mounts and drill out the holes to mount the engine to the motor mounts. First we'll need to place the motor mounts on the firewall. Use 6-32 x 3/4” screws to secure the motor mount to the firewall (picture #1). If you look at the picture you will notice that one side of each mount has a small “wall” on it, this helps to make the mount stronger. You will want to make sure that this “wall” is placed to the outside of the firewall.

What we will do next is place the motor where it is supposed to sit on the mounts so that we can mark the location of the motor mount holes. In my experience in both the real world and here on RCU I've noticed that this process seems to cause a lot of us huge problems. The problems that I've noticed the most is improper distance from the firewall, and more importantly crooked mounting holes in the mounts. Improper distance isn't as critical in this plane because we have an open engine compartment, but in planes that have a cowl this can cause huge problems. In a cowled engine this is really difficult, because if the motor is mounted too short the spinner will rub against the cowl and if it's mounted long it leaves a huge gap between the spinner and the cowl which looks just awful (IMHO). The second (and more important in my opinion) is having the mount holes placement incorrect and/or drill crooked. If the mount holes are placed incorrect you will have a hard time even mounting the motor in the mounts. And if the holes are drilled crooked huge problems can occur. When the holes are crooked and you put a screw in the mount the stress placed on the mount can actually crack the mount in flight, and then having the motor fall off. Definitely not good.

Before we can place the engine on the mounts to measure it we need to install the spinner backplate onto the motor crankshaft. Picture #2 shows the backplate and the crankshaft spacers that come with the spinner. It's very rare (ok, next to impossible) to find a spinner backplate that will fit exactly on the crankshaft and this is where the spacers come in. The slide over the crankshaft so that the spinner backplate sits correctly on the shaft. Finding the correct space is very simple. Just find the spacer that fits your crankshaft and slide in into place. Picture #3 shows the gap in the spinner backplate on the crankshaft of our motor. Picture #4 shows the spacer that I selected to use here, and picture #5 shows the spacer and backplate in place.

So I'm going to try to help give you a pointer or two to help avoid these problems. While I'm no expert at this, I've found a few tricks that help me. First determine the distance from the firewall your motor will sit. In most models it's usually easier to measure the distance from the firewall to the back of the spinner. Most kit instructions will give you this distance, but if not it's pretty easy to determine this yourself by getting the measurement off of the plans (of course you want to measure it twice right? ). In the case of this kit the distance was given to us in the instructions, and that was to locate the back of the spinner 4-3/8” from the firewall. I have always had a very hard time using a ruler to measure the distance from the firewall to the backplate of the spinner. No matter how carefully I measure the distance, it always seems to be wrong when I get it all put together. I finally came to the conclusion that wasn't how accurately I measured the distance, but instead it was HOW I was measuring the distance from the firewall to the backplate. When I tried to measure using a ruler I just couldn't get the ruler into a position to get an accurate measurement, so I needed to come up with a better way to measure this distance. Picture # 6 shows my solution, I cut a craft stick to the length that I will set the spinner backplate away from the firewall. In picture #7 you can see how easy it is to get the motor set in the correct place now (I do apologize for the blurry picture, but you can still get the idea of what's going on). Even though we have this stick cut that doesn't mean that we need to forget about accurate measurements, “measure twice, cut once” still comes into play here. So check several times to make sure that the motor is in the correct position. In picture #8 you can see another tool that is hard to live without once you have used it. This is the Hobbico center marking tool. It has an outer tube that ends in a cone that you place in the hole of the motor mount, and on the inside there is a small drill bit that you extend out and drill a small guide mark with. Picture #9 shows marking a hole. This tool makes it easy to accurately mark the center of your holes. It's really important to get your mounting holes centered on the motor. If you don't the stress placed on the motor mount will cause it to break, and usually in flight is when it will break. When you drill the holes in the motor mount you want to drill them perpendicular in the motor mount. If possible you will want to use a drill press to drill out the mount holes. Clamp down the motor mount so that it is sitting level when you drill the holes. You can use a square to check that drill bit is at 90° to the motor mount. When you are satisfied you can now drill the mounting holes. Don't rush your drill, but rather drill the holes only as fast as the drill bit will cut (picture #10). If you don't have a drill press you can still get fairly accurate holes. Position the motor mounts in a vise and use a hand drill to drill the holes. Just keep an eye on the position of your drill and take care to keep it as straight as you can while you drill. Picture #11 shows the completed holes, and picture #12 shows how the motor sits with the mounting bolts in place.

More posts coming soon.
Pictures
1. Positioning the motor mounts on the firewall.
2. Spinner backplate with provided crankshaft spacers
3. Gap between the spinner backplate and the crankshaft
4. Placing backplate spacer on the crankshaft.
5. Spinner backplate in position on motor.
6. Spacer created to position motor on motor mounts.
7. Using spacer to set motor in place.
8. Center marking tool
9. Using the center marking tool to mark where to drill the motor mount
10. Drilling mounting holes in the motor mount
11. Motor mounts after engine mounting holes have been drilled
12. Test fitting the motor on the mounts



Until next time

Ken