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Inspecting the Engine Mount, Harmon Rocket

I had a prop strike and have removed the engine for tear-down inspection. Now would be a good time to take a close look at the engine mount and inspect for cracks.

The mount is powder coated and I am told that dye penetrant inspection will not work. The HR has the gear mounted to the engine mount, so removal of the mount is complicated -- I would rather inspect the mount on-aircraft if possible.

Any suggestions on how to be assured there are no cracks in the mount?

Thanks!
 
no shortcut here...

Sorry to hear about your incident.

The powdercoating has to be removed to check for cracks. Taking the mount off is almost as simple as taking the 6 bolts loose and there ya go.

I would get the thing off, remove the powdercoating, and re-paint using high quality epoxy primer - top coating is optional if you use the better primer.

If the part is cracked, it will be around the lower outside attach points, and maybe around the upper ends of the leg sockets too. You could strengthen these areas with gusseting - email me offline if you want to see how we did it on the final version of the F1 mount. No, the mounts do not interchange.

BTW if you need a new prop, the 2 blade Hartzell BA unit is the ticket.

Carry on!
Mark
 
I highly recommend Mark's suggestion regarding the upgrade to the BA Hartzell. It will get you 8 knots on the top end and MUCH smoother operations.
 
Check with NDT companies

Before removing the powder coat, I would check with several local NDT companies. For sure dye penetrant inspection will not work with powder coating, but magnetic particle inspection might.

If you do have to remove the powder coating, you can probably get it re-powder coated locally. The Cardinal powder coat color code is posted on Van's website third item from bottom:
http://www.vansaircraft.com/public/confaq.htm
 
Well, maybe...

Before removing the powder coat, I would check with several local NDT companies. For sure dye penetrant inspection will not work with powder coating, but magnetic particle inspection might.

If you do have to remove the powder coating, you can probably get it re-powder coated locally. The Cardinal powder coat color code is posted on Van's website third item from bottom:
http://www.vansaircraft.com/public/confaq.htm

It seems that powdercoating an engine mount is a particularly bad idea, considering the powdercoating will likely make it difficult to see cracks as they occur; the powdercoating will stretch more then the metal will, and conceal any cracks. This is very bad juju.:eek:

Paint does not have this tendency, thus making it a better choice for stressed welded assemblies like engine mounts, assuming that one would actually WANT to see any cracks.

I work as maintenance lead on a couple of very old aircraft, and I am very happy to NOT see anything powdercoated on those machines: if it's cracked, I want to SEE it. YMMV, of course.

Carry on!
Mark
 
I agree with Mark

I painted several areas where I would want to make a crack more obvious white with the idea that a crack would be easier to see visually. Sometimes there are more important considerations than how good it looks.

Chris M RV-4
 
I have made this repair. Warning, the gearleg ID will shrink from welding.

1. Turn a chunk of copper with a lathe .001-002" larger than the OD of the gearleg. Insert this in the bottom of the socket which is to be welded. The weld will shrink, this will help allow the gearleg to still fit after the weld has cooled. Keep in mind the top of the gearleg has to pass thru this area so you have to be mindful of the OD at the top.

2. Clamp the gearleg to shut the crack closed. Weld. Then grind off the weld bead.

3. Fabricate a split ring from 4130 that will slide over and fit around the bottom bolt tube and existing welds.

4. Weld the split ring on top and bottom around the opening of the gear leg socket.
 
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Powder coating removal

There is a spray that is used to remove powder coating. It's at any of your fine car stores, "gasket remover" is what you need. I can get the PN for you if you need it.
Best,
Brian
 
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