N 96872

[TimHicks]

Re: N 96872

I've had a chance to fly several flights now. I still feel like I'm walking on clouds.
But one thing that has come out of the shakedown flights is that it looks like I can't live with my existing cowl bump situation.
Putting the C85 on the airplane had the effect of moving the spark plugs farther outboard (than the A65).
In two locations, there is not enough clearance and the cowl bumps are getting holes melted in them.
And worse, one of the spark plug wires is getting abraded.
So I need to do something.
The existing fiberglas cowl bumps are less than 10 years old. But I would need new, wider cowl bumps because when I move them outboard to cover the new sparkplug positions, they still have to cover the inboard side of the existing holes.
So I decided that I should try to make aluminum cowl bumps.
How hard can it be?

[TimHicks]

Re: N 96872

So a grabbed a pine 2x6 that was laying around and whittled out a recess.
Then I got a flat piece of 0.020" aluminum that had been laying around the hangar that someone told me was "soft" for doing this sort of work. After trying different hammers that I had around, I ended up just using the round part of the ball-peen hammer. But sure enough, it worked it's way into the recess pretty well. Ultimately it split before it was deep enough to be useful to me. But I learned a lot from this first step.

At this point, I ordered 3 2'x4' sheets aluminum from aircraft spruce. 3003H14 in 0.025 thick, 0.032 thick and 0.040" thick.

[TimHicks]

Re: N 96872

While waiting for the new aluminum to come in, I still had one more piece of the 0.020" aluminum (of unknown composition), so I thought that if I had a male buck, I could smooth out the bumps caused by hammering into the recess. So you can see that I enlarged the female buck and made a male buck that roughly matched the female.

I screwed the male buck to a flat piece of plywood thinking that I could hammer the flange flat onto the plywood.
You can see how poorly that worked. Notice the compound curve part of the aluminum is smother than the previous experiment. But hammering the flange obviously didn't work at all.

[TimHicks]

Re: N 96872

Once I got the new aluminum, I started by trying the 0.032" sheet. I also decided not to screw the sheet to the buck in case the material wanted to pull towards the center. So I clamped a coverplate over the flat aluminum and started pounding away.
The result came out pretty good. But so far the deepest bump that I have made is only about 1.10" deep. From measuring the airplane, I knew that I needed 1.25" to 1.50".

[PA1195]

Re: N 96872

I've been told there's a short spark plug available for these installations. Maybe you already have them. I think these are the ones, but there may be others: http://www.aircraftspruce.com/catalo...testplugs8.php

[TimHicks]

Re: N 96872

So by now, I was starting to see that this was probably going to work.
I made the female buck even deeper and decided it was time to work with the 0.040" material.
And I made a new tool that I called the "flange buck". I just traced around the male buck on a piece of plywood and cut 0.04" wider than the line (roughly).
Then I incorporated a 3 step process
1. pound the flat aluminum into the female buck
2. flip the aluminum over onto the male buck and tap out the bumps from the outside.
3. Put the aluminum into the flange buck and pound the male buck into it with a sledgehammer.

This worked pretty good and got me to about 1.25" deep with a pretty smooth surface.

[TimHicks]

Re: N 96872

So then I thought, "Why am I wearing myself out by pounding the aluminum into the female buck in the first step? Why not just skip straight to the third step with a hydraulic ram?"

Well, I guess my cover plate wasn't stiff enough. But even if it were, it seemed pretty obvious to me that this wasn't going to work with just one step.

[TimHicks]

Re: N 96872

So I decided that I needed to get 75% of the depth in step 1 by pounding the flat aluminum into the recess. Then finish it by using the ram to push it the rest of the way. Also notice that I put more screws into the coverplate to try to keep the flange flat.

Although it gave me the surface finish I wanted and the depth, I didn't have enough control over the ram (combined with the springiness of the aluminum and all the wood). So I busted another part.

But this gave me the chance to measure the thickness of the aluminum at its thinnest. This piece started out at 0.040" and it measured 0.028" at the split.

[TimHicks]

Re: N 96872

So the process that I ended up with was the 3-step process that I mentioned earlier.
Two differences were that I used a MappGas torch to warm the aluminum slightly (too hot to touch, but I didn't have any way to know the temp) in the first step (pounding the aluminum into the recess).
And I gave up on trying to get to 1.50" deep.
So I got two bumps that started from 0.040" 3003H14. They both ended up at 1.30" deep.
It looks like it takes about 4 passes of primer and sanding and primer and sanding, etc. before most of the low spots are filled.

They're not perfect. But I think that I'll install them on my airplane (in the correct location for the new engine)

[Bigdog]

Re: N 96872

You're on the right track with annealing it after it gets work hardened. In a class I took we annealed the aluminum with an oxy-acetylene torch. First use a pure acetylene flame to coat the AL with soot, i.e. carbon. Then use a neutral flame to burn off the carbon. The temp to remove the carbon is the right temp to anneal the AL. IIRC it's around 600 deg F. Feels kinda weird but it works.

[TimHicks]

Re: N 96872

I don't think I was annealing it. I was so scared of melting it, that I was staying on the cool side. I doubt that I ever got over 300°F.
I was just assuming that it might deform more easily warm than it would cool.

[N96337]

Re: N 96872

I was thinking the whole time while reading this....anneal that aluminum and you'll have better luck. Another thing I'll do when I'm doing press work, (like you did with the male/female buck and the ram) is grease the bucks...it does help. As for leveling out the bumps, a nice piece of wood rounded on the end with a generous radius will make a nice mallet to "TAP" out the dents. It takes patience, but it's fun in the end! I like what you came up with!! That looks good Tim!
John

[TimHicks]

Re: N 96872

Grease on the bucks! I wish that I had known or thought of that. That would have been worth trying!

Also to answer PA1195's suggestion, I found this picture on the web.

It looks like there is, indeed, a shorter plug that is approved for the C85. I've currently got the one on the right. I'm going to get one of the ones on the left and try it out in my tight spots to see if it gives me some much-needed room. The dimensions in the sketch illustrate something else. But you can see that the harness side of the 37BY is shorter, too.

[PA1195]

Re: N 96872

Grease on the bucks! I wish that I had known or thought of that. That would have been worth trying!

Also to answer PA1195's suggestion, I found this picture on the web.

It looks like there is, indeed, a shorter plug that is approved for the C85. I've currently got the one on the right. I'm going to get one of the ones on the left and try it out in my tight spots to see if it gives me some much-needed room. The dimensions in the sketch illustrate something else. But you can see that the harness side of the 37BY is shorter, too.

The former owner of my T used the suggested plugs to gain the needed clearance. I'm finishing a C-85->O-200 STC overhaul and it was suggested I replace all the used plugs with the new short variety (also to help diagnose any future A/F or oil issues). Their extended nose is claimed to help with lead scavenging but I can't confirm the claim.

One manufacturer's info: http://www.tempestplus.com/portals/0...3-07-01-13.pdf

Another opinion thread from another Forum re: short plugs: http://www.supercub.org/forum/archiv...p/t-35590.html

Gary

[3Dreaming]

Re: N 96872

These plugs were designed for a certain series Lycoming 0-235 for lead fowling issues.