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Installed Engine Mount – 6 hrs

July 22, 2012 Leave a comment

Sunday, Jul 22, 2012

I ordered some edge seal material from McMaster-Carr last week and it arrived so I tried installing it to see how it would work with the canopy. I want it to seal the gap along the sides to prevent major air leaks and stop water from leaking in but I don’t want it to interfere with the latching of the canopy. The material is pretty nice with a reinforced edge grip and a soft hollow round seal attached. The part number is 1120A812 for those interested. It attaches nicely where the edge is .062 thick. In the overlap areas where the seal is thicker the edge grip does not work so I cut pieces and installed them where the edge thickness allowed. I also cut short pieces and removed the edge grip so I can bond them on in the other areas, but I will wait to install those. You can see the strips installed along the two sides in this photo.

Afterward I reinstalled the canopy on the fuselage and tried closing it. It turns out the seal is a little too thick near the aft end where the gap is the least and it prevents the canopy from seating flush without a significant amount of force. I pealed the seals back about one foot from the aft end and the canopy closed fine so I need a slightly thinner seal for the rear foot or so. I’ll have to see what McMaster-Carr has that might work.

Next I primed and painted a few parts; specifically the battery clamp and spacers and the doubler strips for the rear canopy window. Here are the battery parts painted flat black. I forgot to take a picture of the doubler strips but they are gray on the inside surfaces and black on the side that mates to the plexiglass to give it that “black-out” look.

Moving on to more meaty issues. I had thoughts of drilling the engine mount to the fuselage today but I was uncertain about the best approach. First the mount is unwieldy and hard to securely clamp to the fuselage. Second, the holes must be drilled 3/8 inch through aluminum and steel and you don’t want the drill to wander or the holes to end up oval. I did some research on the web and found multiple recommendations for doing this. Some said just line it up and drill, one used a ¼ ID and 3/8 OD drill busing to drill ¼ holes first then enlarge to 3/8, one used a piece of aluminum tube that was ¼ ID and 3/8 OD as a bushing, and one pre-drilled all holes to 3/16 using the firewall holes as the guide, then installed the engine mount with 3/16 bolts and drilled out one at a time to 3/8. No clear consensus on the best way. Whatever way someone used it seemed to work out OK

I started by clamping and taping the mount to the firewall as best I could after aligning the mount holes to the pre-drilled holes in the firewall. I was leaning toward ordering a drill bushing from McMaster-Carr but that would cost me $20 and another week so I decided to give the simple approach a try. If it didn’t work well on the first hole I would stop until I could get a bushing for the rest of the six holes.

I picked up a new 3/8 inch cobalt drill bit at True Value along with some cutting oil. Then I marked around the pads of the mount on the firewall so I could see if the mount shifted and began drilling the first hole. The advice for drilling steel is drill at slow RPM with high pressure and lots of cutting oil so that’s what I did. My arm was tired after the upper left hole from pushing hard against the drill, but it went through cleanly leaving a nice round hole visible on the inside. I deburred the interior hole edge and put a bolt in with a washer and nut and tightened that corner down. Somewhat encouraged, I moved to the upper right hole. Again watching the markings around the pad to make sure the mount did not shift on me, I drilled the second hole with similar results. After that it was easy. With two corners firmly anchored down I did not worry about it shifting. My drill got tired after the first hole and I had to give a break for about an half hour to recharge a bit. Continuing later, I finished all six holes, all done and looking good.

 

For the lower middle holes I had a small gap between the pad and the firewall as most do. I happened to find some 1.25 OD stainless steel fender washers at True Value hardware that are .045 thick. One of these on each side was perfect after I drilled the center holes out to 3/8. The one on the left below is the original, and the one on the right is drilled.

 

I am very happy to have the engine mount drilled to the firewall. I was hoping to have it mounted before the engine arrives (any day now). I took the engine mount off the firewall and deburred all the holes on the outside and cleaned away any chips. Then I hung it back on temporarily because I still need to drill some holes in the firewall for other accessories. After that I cleaned up the garage to make room for the engine crate which should be here before next weekend.

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