Engine Mount cracked - Page 4

BruceMe · #31 03-28-2017, 08:17 AM

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.

Sam Buchanan · #32 03-28-2017, 10:04 AM

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.

N941WR · #33 09-19-2017, 06:53 PM

While completing my Condition Inspection I noticed a crack.

The crack is on the bottom horizontal tube, just inboard of the short bracing tube that ties the gear leg tube to that horizontal tube.

My engine mount is circa 2009 and supports an O-360. There are no gussets on this mount.

The current manufacture of the mounts, which is different than the person who made my mount, said he now machines the gear leg tubes rather than nesting and welding two tubes.

The mount will come off and be sent to www.super-12.com where Steve will create a jig from my mount to make sure the six firewall bolts and the dynafocal mounts are all in the same place in space. This is important to make sure the mount will bolt back up and the prop/spinner will match the cowl.

Once my mount is in his jig, Steve will cut out the cracked tube and the old gear leg tubes and weld in the new machined gear leg tubes, cross tube, and gussets. Then it will have to be drilled to match my gear legs.

Next time you have your cowl off, please inspect it carefully for cracks.

mbauer · #34 03-02-2019, 08:43 PM

Just found these cracks in my 1998 Syd Nelson RV-6. Hard to see but they are there on both main gear mounts.

Remember reading this thread 9-months ago, was looking for it when a link was provided.

Just wanted to say Thank You to all posted photos and great explanations/examples!

Best regards,
Mike Bauer

Boyd Birchler · #35 03-04-2019, 10:02 AM

My RV7's mount has the gussets. By 300 hours the gussets had cracked and needed to be rewelded. You might rethink the placement of the gussets and the thickness of the gussets. Every time you land the gusset is in compression; perhaps if it was a bit a bit thicker material it would be able to not flex enough to fatigue.

Ironflight · #36 05-18-2020, 08:14 PM

There comes a time in every RV-6's life.....

We were doing the annual on Louise's RV-6 this past week, and sure enough - the cracks have appeared. It's remarkable, actually, that it took over 3500 hours and 30 years for us to see the problem (although there are some reports it might have happened before - but I don't see a previous repair on this mount...), especially since this is kit #4, and there are no gussets.

So the engine is coming off, and the mount will find its way to the Greater Portland area will Russ will work his welding magic, fix the problem, and add the gussets. And meanwhile, we'll do some FWF clean-up. This has been (and will continue to be) a strong, working airplane!

Paul

yarddart · #37 05-20-2020, 03:33 PM

RV 3B engine mount cracks I wonder how many have had to have been repaired?

JonJay · #38 05-21-2020, 07:47 AM

Quote:

Originally Posted by Ironflight

There comes a time in every RV-6's life.....

We were doing the annual on Louise's RV-6 this past week, and sure enough - the cracks have appeared. It's remarkable, actually, that it took over 3500 hours and 30 years for us to see the problem (although there are some reports it might have happened before - but I don't see a previous repair on this mount...), especially since this is kit #4, and there are no gussets.

So the engine is coming off, and the mount will find its way to the Greater Portland area will Russ will work his welding magic, fix the problem, and add the gussets. And meanwhile, we'll do some FWF clean-up. This has been (and will continue to be) a strong, working airplane!

Paul

That is amazing! I am glad I have the gussets as I have made more than a few landings that should have broken something, although I think most cracks in engine mounts are fatigue.
I fancy myself as a decent welder. Then I watch Russ, and realize I am a hack. He is the best and you will get a fine product back.

rocketbob · #39 05-21-2020, 09:01 AM

I had serious cracks in my -6 mount. I welded the cracks after removing the mount, and welded a heavy ring around the bottom of the gear leg and over the cracks after smoothing the weld beads over. Rather than adding gussets I made multiple passes from the bottom of the bolt tubes to the heavy ring. I believe what I came up with is stronger than gussets.

Russ McCutcheon · #40 05-21-2020, 05:57 PM

Quote:

Originally Posted by JonJay

That is amazing! I am glad I have the gussets as I have made more than a few landings that should have broken something, although I think most cracks in engine mounts are fatigue.
I fancy myself as a decent welder. Then I watch Russ, and realize I am a hack. He is the best and you will get a fine product back.

Thanks Jon!