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  #31  
Old 03-28-2017, 08:17 AM
BruceMe's Avatar
BruceMe BruceMe is offline
 
Join Date: Feb 2005
Location: Shawnee, Kansas
Posts: 566
Default Engine Mount Cracking

I've owned An RV-3,4 & 6 all have the combined engine/gear mount. I've had to do this twice now on the -3 and the -6 (the -4 is not old enough yet). It's common/engineered fatigue issue and RV with this mount configuration should inspect for cracked mounts around the landing gear on every annual and I like to look at them every time I have the cowl off. It's really not a big deal to fix actually and you can do it without fully pulling the engine all the way off. If it's simple it should take about a week and $100, two (of both) if you wish it bead blasted to strip it all the way down.

..oh, I personally would avoid "beefing up" these joints. This is a designed break-point. Making it stronger will cause more expensive parts (like airframes/firewalls) to get damaged when you do bad things. It's a _LOT_ cheaper to re-weld a twisted engine mount that rebuild a firewall or throw away a bent fuselage.

My point is that proven and well-engineered designs are built and time-tested for a reason. Alterations, even seemingly well-intentioned and small changes like these have unintended consequences.
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Once RV-3 3456B
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Last edited by BruceMe : 03-28-2017 at 08:38 AM.
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  #32  
Old 03-28-2017, 10:04 AM
Sam Buchanan's Avatar
Sam Buchanan Sam Buchanan is offline
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Join Date: Dec 2004
Location: North Alabama
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Default

I found a small, hairline crack at the lowest weld on the aft side of both gear leg sockets after a few years of flying my RV-6. I watched the cracks for several years and they didn't spread. In spite of not being able to see how these defects could lead to a gear or mount failure, three years ago I pulled the mount away from the firewall far enough to run a weld bead over the cracks.....just because.

By next condition inspection a small crack had appeared at the edge of one of the new welds. I've decided this is something I can live with since this appears to be a compression failure where the mount is very unlikely to ever fail and I've never seen a crack grow to more than 1/2" long in this area. I will continue to monitor this situation but doubt I will ever feel the urge to repair it again.

At least until some sharp-eyed A&P sees it during a pre-buy someday.
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