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Engine Mount Inspection & Refurb

KatieB

Well Known Member
After inspecting my cam, it was decided that 5 years of sitting around did it no favors. (Engines are like people, 5 years of being a couch potato really kill them!) So we pulled the engine, split the case, and all that. A story for another thread. Anyway, while the engine was off I decided to install firewall insulation and pull the engine mount off the plane for a good cleaning and look-over.

While I was cleaning it, I found several areas where the paint had rubbed or chipped off, but there was one tiny crack in the paint that looked suspicious. The paint had split open a tiny bit and looked like it had been pulled apart. This is the joint between the lower left bolt pad and the left gear leg.

0223161929.jpg


I showed this picture to a representative for Aerospace Welding Minneapolis a couple weeks ago when I was at a maintenance technicians conference. They specialize in certified engine mount repair. He said it does look suspicious and that I should do a dye penetrant test on it.

So, I did. We had a Magnaflux brand dye penetrant kit at the shop. You can buy one from Aircraft Spruce for a little over $100.

First, I stripped all the paint off using a chemical stripper. Apparently, if you use sandpaper or other mechanical means to get the paint off, you can fill in the crack enough that the dye won't penetrate it. After stripping the paint off, the welds looked great. There was nothing there to make me suspect anything, other than I just knew better.

0313161531.jpg


I applied the dye penetrant to the area around both gear leg sockets. The other side had a bit of rust showing beneath the paint, so I wanted to check that side too. Lo and behold...

0313161639a.jpg


Both sides were indicating cracks. So I took it to a local welder who has experience with repairing experimental aircraft engine mounts and welded spar boxes. He had it fixed in less than an hour. No big deal! But boy am I glad I checked it. These cracks were in a really tough spot to inspect when the mount and engine are on the plane. Mirrors and cleaning are definitely required. If your engine is off the plane, don't skimp-- clean up your mount and check it all over. The RV-3, -4, and -6 mounts are known for cracking in this area, so I was suspicious of it automatically.

By the way, the dye penetrant thing sounds complicated but it's really simple... I just followed the instructions that came with the kit. The cracks show up like magic!

As for painting the engine mount? The rep from Aerospace Welding Minneapolis said that certified aircraft engine mounts are almost never powdercoated. This is because powdercoating can make cracks like this very difficult to spot. And, powdercoat is really difficult to strip off in the event of an inspection or repair.

Dave Paule saw my picture and he decided to weld some gussets on his mount, and others have done the same thing. I thought about this, but decided to stick with the stock design this time around. The airplane had a history of gear shimmy, but it was fixed with wood stiffeners. And I plan to keep it on pavement most of the time. I'm not quite sold on gussets yet because from all my experience with repairing RC models, I know that a structure needs to flex a little bit, and it usually re-breaks next to the beefed up repaired area. So, we'll see how the new welds hold up.
 
Mount paint

After you chemically stripped the old paint did you need to neutralize the stripper? Also, what paint and primer if any did you use.
 
Katie,

I had some scuffs on my new gear leg. I used some paint that I had on hand (after filling) from LVP to touch it up. It?s a really close match and I really can?t tell where the painted area ends and the powder coat begins. I would recommend taking that route.
 
"Dave Paule saw my picture and he decided to weld some gussets on his mount, and others have done the same thing. I thought about this, but decided to stick with the stock design this time around. The airplane had a history of gear shimmy, but it was fixed with wood stiffeners. And I plan to keep it on pavement most of the time. I'm not quite sold on gussets yet because from all my experience with repairing RC models, I know that a structure needs to flex a little bit, and it usually re-breaks next to the beefed up repaired area. So, we'll see how the new welds hold up."

Katie, Good post and follow through. I have done two RV-6 mounts with cracks. I removed, stripped and inspected. Nice tip on the stripper and bead blasting material filling cracks. In regards to the gussets, Vans sells a gusset made to weld onto the bottom triangle and along the tube. A very nicely made part that would be hard to replcate without a example in hand. They also sell it for the cost of material, like 5.00. Vans recommends this modification and it has been incorporated in the newer -7 mount. I understand you are most likely past this point in your refurbishment but wanted to let you know it was available to you and others in this position.

PS...not sure if Vans makes a gusset for the -3 mount but with one in hand, it might help in making one.
 
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Just curious where you see the crack (or how you see it.)?? I presume someplace in the dye but I don't understand what that blotch his telling us. Thanks.

edit: oops. old post.
 
Yeah, that post was from 4 years ago! I just happened to open up VAF today and saw it had been revived.

The cracks looked like hairline cracks in the paint, which is why I stripped it all off and used dye penetrant. The photo is blurry, but inside the red blob is a dark area that follows the crack line. I don't remember what kind of paint and primer I used, but it wasn't fancy. I cleaned it up really well with acetone and shot it with industrial strength Rustoleum, probably.

If i had to do this over again, I would install gussets, because why not. An ounce of prevention... But the stock design is 40 years old and I wasn't planning on operating off of turf very often. The plane had previously been based on a grass runway.
 
Here's a photo of the gusset I added. The arrow is pointing to mine. The other gussets were part of the engine mount as I received it from the factory.

I used .090 4130 simply because that's what I had on hand. I'd have used .063 if I'd had any.

EhnOGMR.jpg


The welding was hired out. We put one of these on each side of the engine mount. Note that this is for an RV-3B.

Dave
 
Dave. Did your welder do the work in a jig? I have a 3B with the factory conical mount that I would like to reinforce. The only gusset on my current mount is the little one shown in the far right of your photo. Neither the triangular one or your new one. I am also considering adding one at the top of the gear leg socket in the cluster where the mount bolt is.

Very nice work, by the way.

Jim
 
engine mount gusset

Here's a photo of the gusset I added. The arrow is pointing to mine. The other gussets were part of the engine mount as I received it from the factory.

I used .090 4130 simply because that's what I had on hand. I'd have used .063 if I'd had any.

EhnOGMR.jpg


The welding was hired out. We put one of these on each side of the engine mount. Note that this is for an RV-3B.

Dave

what is the tack welded washer for?
 
Is it just my screen resolution? Or does it look like there are holes in that weld below the red arrow??? If so, that would be a big concern. Maybe just the photo resolution and lighting I hope?
 
Is it just my screen resolution? Or does it look like there are holes in that weld below the red arrow??? If so, that would be a big concern. Maybe just the photo resolution and lighting I hope?

No holes in the actual part. It was a good weld. The photo came from a reduced-size original that had been posted on VAF, made into a PDF, screen-shot from the PDF and then reduced again for this thread. All in all, kind of amazing it's legible at all.

I think the washer is fully welded on its forward face. We're looking at its firewall face here.

Dave
 
Dan. I don't think anybody on VAF minds an extra set of eyes asking questions about anything. I saw that in the weld too but realized it was the lighting. While all I can say are great things about Dave's RV-3B project thread and workmanship, I can't speak for him. But if I were a guessing sort I would gather he doesn't mind anybody asking about something they might see and have a concern over. That's one trait I have seen repeatedly in confident competent builders and mechanics.
 
I want all the eyes on the project I can get and any concerns raised. Can't predict my response but at least I'll consider them. There ain't no way I know everything and I'm well aware of the hazard of looking at something and not seeing it.

Thanks!
Dave
 
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