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Engine Mount Crack

dlomheim said:
While doing an oil change last week I found an engine mount crack, so ordered in new tubing and will get that repaired after it arrives, etc. Just wondered if any others have expereinced this at all...
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I think you'll find inspecting for cracks around the landing gear socket is a must-do inspection item.
 
Hi Doug,
I did a quickie search for cracks, because I seem to remember seeing a thread here or there on cracks in the mount. (google this -- site:vansairforce.com crack mount) and it came up with several good threads. There are some threads on 6's, 4's and 7's. Nothing systemic shows up, and a few go back in years.
 
Mount Cracks

Doug,

I had to repair my 3 last year. I added in some strengheners as per common practice here in the UK.
My 3 was the 3rd RV in the local area to have cracks.
The Local fix here is to add in extra gussets as per the new factory RV7 mounts plus extra torsional gussets to alleviate the torsional twist under braking.

Pm me if you have any queries.

Rob
 
I have a friend with a 6 who operates out of an old WWII field that is in need of repaving and he has had to have his mount repaired twice in a couple hundred hours. I guess the legs move a lot and the mounts fatigue. They probably need some strategic reinforcement somewhere to increase their fatigue resistance. So this is nothing that unusual.
 
Mount cracks

I bought my RV-3 with a broken mount...cracked at the top end of the gear leg tube. The logs showed it had been repaired twice before, but they welded it while on the plane and the welds did not hold. I ordered a new mount and gear legs from Vans, had them powder coated and then installed, and I can tell you it was a huge job. The firewall needed considerable adjustment to make the new mount fit up.
It is all new and flying now. I put gear leg stiffeners on the legs (per the plans) to stop the "walking" and "wobbling" that many experience. I have to pull the cowling off to change the oil in the next few weeks, and I am hoping to find all is well under there, but I have resolved to make it an inspection item with some frequency for sure.
Inspection of the broken mount indicated the failure was most likely a side-load, possibly cross wind landings. Also, it had an IO-360 and a CS prop on it for most of its life which it was never really designed to carry...about an extra 40lbs (maybe) hanging off the mount.
Good luck with your repair, the new mounts are designed a little different, and I am hoping that the few hard landings I have had while learning the ropes of the RV-3 have not affected it. :D
Dave
 
dacronwall said:
I bought my RV-3 with a broken mount...cracked at the top end of the gear leg tube. The logs showed it had been repaired twice before, but they welded it while on the plane and the welds did not hold. I ordered a new mount and gear legs from Vans, had them powder coated and then installed, and I can tell you it was a huge job. The firewall needed considerable adjustment to make the new mount fit up.

Dave
Click to expand...

How do you "adjust" a firewall? Did the holes not line up?
 
I had my RV-6 engine mount repaired last year. Had gussets welded in around the gear leg sockets to strengthen it (or, I guess, to move the point where it flexes to somewhere else. Hmm...) It's a pretty standard mod, as other posters have said, inspection for cracks in this area should be a standard action, and you probably shouldn't be too upset if you find them.

About 1300-ish hours when I had it done.

- mark
 
"adjust firewall"

Yes, the holes did not line up. My airplane is 30 yrs old, and the engine mount is slightly different now. It is better, stronger, I think....but it was a lot of work to make it fit up right. And the engine hung 3/4" lower when finished so the cowl had to be cut, and re-fiberglassed to line up with the spinner.
My original mount would not have been airworthy to attempt welding a 3rd time, new was the way to go...it just took a while, I don't regret doing it that way.
Best
Dave
 
RV3 engine mnt cracks

That crack is typical of an RV3 that does not have the two additional engine mnt-to-firewall attach points near the center of the firewall. These were introduced in the design around 1985 or so. The specific location is adjacent to and inboard of each upper gear leg socket, on the cross-bar, making for six bolts in all attaching engine mount through firewall. They prevent the gear leg socket from rocking back and forth under landing loads. They would appear in the photo if present, but I don't see them. Without these, the engine mount will likely keep cracking in that area if you operate on unimproved strips or have a normal complement of hard landings. There should be a structure in the fwd cockpit that distributes the load from the center firewall into the fwd cockpit floorboard. Best to contact Van's for details.

- Steven
(850 RV3 hours - another one last Sunday!)
 
Mount Cracking

We repaired cracks near the gear mount sockets in our "short leg" -4 at about 1100 hours. The -4 has the six bolt mount. You might chat with Russ McCutcheon here on the forums as his shop builds the engine mounts for Van's and he was very helpful (as were the tech support folks at Van's) when we repaired ours. I chose not to install stiffeners since I didn't have a structural analysis of the assembly with stiffeners in place and was concerned about the effect they may have on loads at the socket. Anecdotally, fatigue damage to this area seems more prevalent in aircraft operated off of grass fields. It's definitely an area that requires careful inspection.

To facilitate visual inspection, I stripped the mount of powder coat (it was powdercoated black) and used contrasting pimer (grey) and finish colors (white) after repairing the welds. The cracks were almost impossible to see in the black powdercoat, the only visual evidence was some grease that had oozed through the cracked weld. After the mount was stripped and cleaned, a dye penetrant showed the cracks clearly.

Cheers,

Vac
 
omrsramsay said:
How did you strip the powder coat?
Click to expand...

John,

Best to chemical strip it and then lightly bead blast. I just used Action Metal down in Hubbard OR to do mine. They do good work. Then had it powder coated again.

During the inspection this year I spotted what I thought were cracks in the mount at the gear tubes. :mad: Long story short, I had the WD-762A (L&R) reinforcing gussets welded on. These are standard in all of the RV-7 & 9 mounts, but the 3, 4, 6, didn't have them.
 
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