When we last saw the oil cooler, it still needed a brace to strengthen the inboard corner and keep the baffle from cracking under load. I happened to have some 3/8" OD, 0.058" wall 4130 tube on hand, so I cut off a chunk and commenced to turn it into an oil cooler brace.
First I hammered the ends flat, which is easier said than done when you're talking about thick-walled tube with a small diameter. I put John Henry on the MP3 player while I did the 30-minute blacksmith power workout.
Heat helped me bend the ends to the correct shape. It took about twenty iterations of heat / adjust bend angle / force-cool with compressed air / carry over to airplane / test fit / repeat.
Once I got it pretty close, I drilled the attachment holes and proceeded to fine-tune the fit so the fasteners would line up exactly.
After much tweaking, I finally got it to fit perfectly. Success! (pay no attention to the temporary hardware shown in this photo)
Once I had the right shape, I polished off the worst of the hammer marks:
Then I heated the ends red-hot and let them cool down slowly to room temperature… one end at a time, obviously, since I had to keep the burning hot metal in the vise.
The intent is for this this to anneal the metal and relax the stress risers caused by hammering and bending it to a new shape. The better to prevent cracks, or at least that's the idea.
After annealing, I cleaned and scuffed the part, then shot a coat of primer followed by two coats of enamel. In between coats I let it sit under the heat lamp to really bake on the finish.
The topmost screw on the rocker cover – seen here from outside the baffles – is where the brace attaches to the cylinder head.
I had no luck sourcing the correct aircraft-grade machine screw (MS51957-85, stainless, 1/4-20 thread, 1.5" long) from any of the usual mail order places, but surprisingly enough was able to find it locally at a surplus aircraft hardware place on my lunch break. I must be living right this week. Here it is next to the original factory screw:
Luckily the cylinder casting is tapped all the way through, so the longer screw protrudes on the inboard side of the head as if it was a stud, and the brace attaches with a nut and lockwasher. On the baffle end, I'll rivet on a nutplate the next time it's convenient.
Even with temporary hardware, this brace seems to do a great job of removing that last bit of play in the oil cooler mounting. After this I probably really could drag the airplane around by the oil cooler, and now I even have a place to attach the chain!