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RV-4 Gear Leg/Engine Mount Cracks

jliltd

Well Known Member
A good friend of mine bought an RV-4 last month. He just started preparing a paint job on it and found what looks like cracks at the top of the landing gear where it joins the engine mount. The aircraft has the original short gear. He sent me some photos of the area.

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Are there any reinforcement type fixes for this? Welding the crack. Welding in gussets. Etc.... ?

Any advice would be appreciated.

Jim
 
It appears that your gear legs have already been redrilled and welded. I would suggest maybe a new improved long leg mount from Van's, especially if you are running 180 hp.
 
I think my suggestion for him woukd be:

"I would remove the paint / powdercoat over the affected welds and get a closer look first.

Affer removing the paint a close examination might reveal the crack is only in the paint. If the finish is powdercoat it might be even more probable since powdercoat is very brittle.

If there are real cracks my Plan A would be to remove the gear legs from the engine mount and then have an expert welder run a new bead along the visible cracks. For this process I would specify a TIG welding machine. Stay away from a MIG wire feed welder because it can cause embrittlement in the steel. Of course a farm type AC/DC arc welder would ruin the whole mount. Oxy-Acetilene gas torch welding would be acceptable as long as the operator uses a rosebud tip to heat the whole area before and after welding to normalize induced stress. So TIG is preferred and gas welding is an acceptable alternative. Have the expert welder pick a welding rod of the type correct for chromoly steel. And make sure the welder doesn't go crazy trying to do a super chingon job with too much chicle. Too much welding might warp the structure.

Then repaint and keep an eye on the area by inspecting at every oil change interval.

If cracks still show up later you could look at adding gussets in a couple of places.

The ultimate option would be to upgrade to the newer long landing gear from Vans."
 
Before you consider repairing the existing mount you should check the gear leg alignment. It appears that the gear legs were drilled initially, and at some point those holes were welded and new bolts were drilled. This would lead me to believe that the initial gear leg alignment was bad, and therefore re drilled. Did they get it right the 2nd time? The older -4's and -6's did not come with pre drilled gear legs, alignment and especially drilling those holes was a real challenge. You are going to need to remove the engine and mount regardless. Take a look at the tire wear, that may give you an indication of gear alignment.
Considering the welding required and powder coating, you may be better off in the long run by just replacing with new.
 
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One could simply clean up the powder coat and TIG weld the repair in-situ, then spot paint. If you ran the weld bead up to the top cap via a small triangular gusset that would add some strength. Or you can take it all apart and make it into a much more complicated project.
 
Could there be any danger to the engine or avionics by welding The crack without removing the engine mount?
 
RV4 Mount Issues

It seems there are a reasonable but unqualified number of RV4s out there with cracks in the gear and engine mounts. You might want to do more than a quick review of your options. Those mounts are only available from Vans, the mount manufacturer can't sell direct, and he just made and shipped 4 to Vans but I think they are all spoken for.

I suggest you call Vans and check with them. You might also contact Marvin at SmokeSystemsHelper https://www.smoke-system-helper.com/ He is going through a very similar but more obvious situation as we speak.

Good luck!

Bill
 
Could there be any danger to the engine or avionics by welding The crack without removing the engine mount?

I've welded engine mounts and other things on airplanes and no there aren't any issues like this. How could there be? Master is off and the airframe is grounded to the welder.
 
A&P tig welded a similar crack on my RV-3 with the engine in place. Simple, quick repair! That was 3-4 yrs ago and no further problem.
 
I would also clean off the spots first to remove the powder coat. It could be just a crack in the powder coat and not in the tubing. Been there done that as well.
 
That hole some of you are saying was a previous hole for the gear leg bolt is not what you think, it?s actually a rosette weld that?s holding that socket in place. I see this gear socket has a cuff added to the top to increase edge clearance for the bolt hole, I?ve done that to several of these during repair visits to my shop that where drilled to close to the edge. Chances are good that I not only built this mount but also repaired it at some point in the past.

Start by removing paint in the local area and hitting it with die penetrant test, if it?s cracked then have your local TIG weldor weld it up using ER70S2 filler rod. If you don?t have a trusted local weldor then send it to me for repair.

If it is broken there be sure to check the status of your lower corner and two center attach points/brackets behind the firewall, if these especially the center ones are broken the mount will flex under landing loads and won?t live to long.
 
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