“No bird ever flew nonstop from New York to Tokyo, or raced 15 miles high at triple the speed of sound.                                                                                                   
  Birds do something else.   They do not conquer the air; they romance it..”

Peter Garrison

Jur's RV7 Aircraft Factory
3497 hours and counting

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04/04/26 - Drill rear line top plenum + oil cooler cutout positioning - 5h30

Written on . Posted in 6.12 Bill Lane Plenum.

 With the sides of the plenum drilled, the inclination of the plenum is set and I can proceed with drilling the aft line of fastener holes. This will be #6 screws. For now I have drawn a reference line where I would like the holes to be on the flange of the epoxy and drilled from the other rear side. Takes some patience to measure but came out fine as you can see in the image.

Here the rear line is drilled except for the holes on the pilot side where the CB-705B oil cooler brace bracket will be positioned. 

 

For these last holes, I had to take a decision on the height of the oil cooler as the bottom line of the oil cooler brace bracket is also the top line of rivets for the oil cooler doubler behind the baffle.
It took a lot of positioning and evaluating the best spot. With the Bill Lane Plenum, the plenum cover height more or less defines the maximum height of the CB-705B oil cooler brace.
This is as high as I could move. The corner in the right side in the image below defines the maximum. If you would go higher, you get a gap between the oil cooler brace and the plenum cover.
I will finally also add some RTV in that corner to ensure it's sealed well.

Another spot to verify is the opposite side of the oil cooler brace. There is a rivet in the CB-706A left aft case baffle which needs to be below  the oil cooler brace and the side flange of the oil cooler brace needs to be matchdrilled with the CB-706A top holes.

With the height set, I drilled the bottom flange of the oil cooler brace to the cylinder aft baffle CB-705A.

 This is the corner I mentioned above. The flange will be further trimmed down. Not much as the hole in the side is pretty low here.

This is the view from the outside. As you see, the floor of the oil cooler brace is almost at equal height with the plenum top in the rear aft corner.

Here is an image of the rivet hole I mentioned above. Its just below the brace.

 Next I drilled the sides and marked the contour of the plenum top on the oil cooler brace. The top part will be cut away. 
Even with other plenums, I wonder id anyone ever needs that height from the stock piece.

As I mentioned, the FF-709 oil cooler doubler has the top holes in common with the CB-705-B oil cooler brace.
Positioned it

A vise grip helps holding it in place. 

 Another shot of the corner of the oil cooler brace with the side bracket.

 Drilled the FF-709 doubler to the CB-705A aft baffle. Updrilled the top and bottom row to #30

While the doubler was on, I traced the contours for the cut out of the oil cooler hole on the CB-705A aft baffle.

The image below gives an impression on the height of the oil cooler brace in relation to #4 cylinder.

Traced a black line on the top of the baffle to grind away more of the height.

 Reinstalled the brace to cut the 3 holes for attaching the top plenum.

 

Holes drilled #40 for now and brace cut to height.