Dave’s RV-7A Building Log

The annual trip to the Boat Show was today, so I didn’t get much done on the project. I just tinkered with the seat pans a little bit, prepping them for installation.

I unfluted the firewall flange without any problem. I also filed a couple of the flange tabs that stick out just a millimeter past the top forward skin. I also measured the thickness of the top skin plus firewall flange and compared that to the cowl thickness. It seems like a 0.15 shim would work best. I found some some stock that was 0.16 and made some shims. It was pretty time consuming to cut and deburr them.

I also placed the top cowl into position just to check it out. Looks cool.

I continued prepping for fitting the top cowl half. When I tried to put in all of the structure under the forward top skin, I realized I hadn’t cut a hole in the middle rib for the canopy release mechanism. It seems that many builders ditch the mechanism, but I’ll keep it if at all possible. I cut the hole and trimmed the rib as needed. With the top skin clecoed back in place, I measured and cut the hinge for the cowl/firewall joint. I realize now that I shouldn’t have fluted the flange on the firewall. I’ll have to flatten it out. Hopefully the holes still line up OK.

Pete James sent me some more photos of his engine. The engine mount on the taildragger definitely makes it easier to route the fuel line between the pump and the servo. I tweaked the clamps a little bit and got the fuel line to sit better. I’m sure it’s just a matter of tweaking and maybe adding a clamp at the engine mount, although the mount moves independent of the engine. It’s probably better not to secure it to the engine mount.

I also installed a 90 degree fitting into the fuel pump and attached the fuel line from the pump to the firewall. I don’t like the looks of the flex in the line, but maybe it’s OK. I’ll get a second opinion on it.

One of the first steps of working on the cowl is to make sure the engine is in its final position. I re-checked the torque on all of the engine mount to firewall bolts. I haven’t secured the cotter pins yet, just in case I might need to remove it still. I think once the P-mags get here (the check cleared so they must be close) and I install them, I’ll be confident the engine is on for good.

Next up were the engine mount bolts. The instructions say that you can’t use a torque wrench on the engine mount nuts, which is true. There just isn’t enough room. I can barely get a box wrench on them. Torquing from the bolts doesn’t work because the rubber mounts put a lot of drag on the bolts. In spite of all that, I looked up the torque value for AN7 bolts. The minimum value is 450 in-lb! My click torque wrench doesn’t even go that high. I have a beam-style torque wrench that does. I clamped it in the vise and reefed it up to 450 in-lb. That’s a lot of torque. With my shorter wrenches, it would be hard to even get that much torque on the bolts.

With that info in mind, I re-checked the engine mount bolts. The top left bolt was good. The top right bolt seemed like it could use more torque. But that caused the cotter pin hole to not line up. I tried a dozen combinations of washers, but nothing worked well. I finally settled for slightly less torque, but having the hole line up.

When I checked the bottom bolts, I discovered that I hadn’t even tightened them all the way up up against the inner metal sleeve. When I did tighten them, the cotter pin hole was too high on the nut. I removed both nuts and added another washer on each. I tightened both bolts until they were hard against the sleeve and then lined up the cotter pin hole. One side is tighter than the other, but they’re both nicely secured. I bent down the cotter pins on all 4 bolts, so they’re not going anywhere now.

I never thought it would take so much time just to secure the engine mount bolts, but I’d rather get it right. As my family and friends keep pointing out, “There’s only 4 bolts holding the engine on.” Ahhh, yeah. How many did you expect?

I picked up four 1/2″ x 3″ x 20 tpi bolts at Lowes for about a buck a piece. Eventhough they were individually packaged, the threads were really banged up. I spent quite a bit of time with a file cleaning up threads. I then cut 4 chunks of 3/4″ PVC to 2-1/8″. The FAQ on Van’s site says to cut them to 2-1/4″, but a few people on the forum suggested making them slightly shorter for a Hartzell constant-speed prop. The holes in the spinner back plate are larger than the bolts, making it difficult to get the plate positioned correctly. I drew a 1″ circle around each hole so I could center the bolt head. I then temporarily installed the spinner back plate to the starter ring/crankshaft with the PVC spacers and the bolts. It’s ready for cowl fitting.

I next decided to tinker with the fuel lines. The fuel-pump-to-servo fuel line that Van’s supplied in the FWF kit was not long enough. I’m guessing that maybe there’s a gusset on the nose wheel mount that is different than the tail wheel mount? Luckily, Mattituck supplied a fuel line that was a few inches longer. It seems that there are two options for routing it around the engine mount, neither one ideal. For one route, the line rubs on the engine mount gusset and the other route makes the line take some awkward bends. I’m hoping I can install enough adel clamps to make it work. Right now the thing wants to rub on the engine mount and back left intake tube and interfere with the mixture bellcrank.

The fuel line from the firewall to the fuel pump is even worse. The mount for the prop governor is in the way of the fuel pump inlet. Again, Mattituck supplied an extra fuel pump elbow, so I can point the inlet downward. However, that makes the fuel line way too long.

It’s pretty frustrating when these $70+ hoses don’t fit. I know I’m not the first person to install an IO360-M1B clone on a 7A.

I drilled the heads of the bolts for the throttle bracket. Using a new cobalt 1/16″ drill bit made it easy. I used Dan’s trick and threaded a nut part way onto the bolt to help hold the bolt steady in the drill press. I had to file the holes in the bracket a tiny bit to get the bolts to fit. The holes in the sump were just a millimeter closer together than the bracket. I then torqued and safety wired the bolts in place. I was told that this bracket might cause interference with the exhast pipes, but we’ll see.

I next worked on the engine bolts again. I added an extra washer to each top bolt. On the right bolt, the cotter pin hole just would not line up on the nut. I tried two different sets of washers and finally found a combination that caused the hole to line up perfectly.

I started to mess with the breather tube, but it seems that the oil filter adapter that Mattituck uses puts the filter right in the way. I’ll have to see what others have done.

Happy 2006!

I worked on getting the mixture brackets installed. The aft bracket (that holds the control cable housing) installed very easily. I was slightly nervous about messing with the sump bolts, but forged ahead.

The bracket that holds the swing arm didn’t install quite as easily. A tiny bit of extra aluminum around the sump bolt holes was in the way. I carefully used a file and cleared it away. The bracket then fit perfectly. Hooking up the bearing end to the mixture arm was easy. The mechanism works at kind of a weird angle, but it does work very smoothly.