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RV6 Broken Engine Mount

J

JESRV6

I'm New Here
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Hello,

Please see the PDF attached.
While doing my annual condition inspection, I found a complete break in the engine mount.
It is a 1997 kit completed in 2004. I bought it in 2007, with 600 hours on the frame and 300 hours
on a new 0-360 from Aero Sport Power, Canada. (Reportedly, it had a 0-320 for the first 300 hours.)
I installed a new IO-360 from Van's in 2000, and the break in the mount was discovered at 553 hrs.
(Three days ago)
The mount, if original, has about 2500 hrs on it. (I’ve put almost 2000 hrs on it)



Option 1:

I would prefer to buy the new kit with the new mount and gear legs, and I may just have to wait the
5 months, Van’s parts department. quoted for lead time. Van’s tech guys tell me the RV6 and 7 use
the same mount/kit.
(Link to kit) https://store.vansaircraft.com/7-dyna-1-o-360-kit.html
RV-7 Dynafocal-1 Engine Mount Kit For Lycoming O-360 Engine


Option 2:
Talk to someone on Van’s shipping list with a lower number, or someone who has it, and doesn't need
it for months (or years), about trading with me (my ship date), to get it earlier.



Option 3:
Is there a certified aircraft engine-mount welder available to inspect and repair it?
Not crazy about this idea since I have to remove the engine and gear anyway.
But it may be doable if the mount was "as good as new"?

Thanks!
J
 

Attachments

I think the question is.

How much do you fly it.
When do I want to fly it.

Now—-#3

Not much —-#2

My .02

Boomer
 
Mine cracked in the same spot. I caught it before it broke completely, but I’d say only a landing or two away from a complete break.

I chose to get it repaired and welded. I believe there is a mod done in the UK, if memory serves, called the Netherthorpe mod which I found and did. There is an image in this thread:
https://vansairforce.net/threads/engine-mount-cracked.147392/

When I found the crack our 6 had about 500 hours TT but I think had been operated off a grass farm strip. I noticed an increase and change in speed/frequency of gear leg shimmy before finding the crack - always check stuff if something changes.

We’re now at about 730 hours and all seems good. I check all visible parts of the mount closely any time the cowling is off, particularly the centre section and firewall & surrounding structure as I think this mod probably transfers extra load & stress there. In the repair I also had all welds on the mount magnafluxed and didn’t find any other issues.

Photos here
https://photos.app.goo.gl/mnjSWMoxRci6yfZ28

Don H
Sydney, Aus
 
auj4 said:
Mine cracked in the same spot. I caught it before it broke completely, but I’d say only a landing or two away from a complete break.

I chose to get it repaired and welded. I believe there is a mod done in the UK, if memory serves, called the Netherthorpe mod which I found and did. There is an image in this thread:
https://vansairforce.net/threads/engine-mount-cracked.147392/

When I found the crack our 6 had about 500 hours TT but I think had been operated off a grass farm strip. I noticed an increase and change in speed/frequency of gear leg shimmy before finding the crack - always check stuff if something changes.

We’re now at about 730 hours and all seems good. I check all visible parts of the mount closely any time the cowling is off, particularly the centre section and firewall & surrounding structure as I think this mod probably transfers extra load & stress there. In the repair I also had all welds on the mount magnafluxed and didn’t find any other issues.

Photos here
https://photos.app.goo.gl/mnjSWMoxRci6yfZ28

Don H
Sydney, Aus
Click to expand...
Paul Dye wrote an article about this in Kitplanes. He took the mount to the manufacturer and had it welded along with some standard reinforcements. The mounts are not made by Vans but by a sub contractor in the RV6 era.
 
I see you are at Hicks.
Do you know Jay Pratt ????

Good resource

Someone on field can weld it for you.

Avery comes to mind. Did some welding for me.

Boomer
 
It seems there are only two types of RV-6 mounts - those which have cracked and those which are yet to crack. If you're in the latter catagory, just look closer!

My mount is a later "RV-7" version after Vans added a couple of extra gussets, but it's still cracked - just in a different place to where the older mounts used to go. And that is after just 240 hours TSN. Sadly, the crack is not in a place that I can access without complete removal of the mount from the engine and airframe. I've been toying with trying to buy a new mount and beefing it up prior to installing it... it's either that or I have to have the machine out of the air for a few weeks while I get the original mount repaired and upgraded.

I don't particularly like the UK SAA modification but clearly it works. The problem is it transfers the load elsewhere... which is normal... and I notice that on a friends' machine that has the UK SAA modification, the rivets are now working on that lower longeron from the firewall back to the spar. But the mount hasn't cracked again (!). I say "again" because after 1200 hours it has already had three repairs. It's a pre-1996 mount without the original gussets that were latter added by Vans.

I'm very interested to see whether the RV-14 mount lasts the distance. Vans must have identified the areas of concern and tried to beef that mount up to avoid future problems (I would hope). And then I wonder - do you go to that extent on the RV-6/7 mount?

As for repairing your one - surely there are some very competent 8130 welders in your area that could help? Saves sending it away and waiting ages for it to come back.
 
As mentioned in Post #4, I put our cracked RV-6 mount in the back of the RV-8, flew up to Russ’s shop, had it fixed, had lunch, and was home by mid-afternoon. But if I were at Hicks, I’d first check with Jay and Bob Avery (if Bob is still around). Bob built a completely new frame for the RV-1 canopy for us back in the day…..
 
planenutz said:
It seems there are only two types of RV-6 mounts - those which have cracked and those which are yet to crack. If you're in the latter catagory, just look closer!

My mount is a later "RV-7" version after Vans added a couple of extra gussets, but it's still cracked - just in a different place to where the older mounts used to go. And that is after just 240 hours TSN.
Click to expand...
Interesting. I have the 7 mount also and there are more than a couple gussets. 1000 hours and no cracks, yet.
Also, considering the size of the fleet, 6’s and 7’s, the reports of cracks don’t match up that all mounts will crack.
I’ve watched mine closely and will continue to, fingers crossed.
I would be really frustrated if mine had cracked at such low hours. Fortunately, Russ is only a couple hour drive if it happens.
 
planenutz said:
It seems there are only two types of RV-6 mounts - those which have cracked and those which are yet to crack. If you're in the latter catagory, just look closer!

My mount is a later "RV-7" version after Vans added a couple of extra gussets, but it's still cracked - just in a different place to where the older mounts used to go. And that is after just 240 hours TSN. Sadly, the crack is not in a place that I can access without complete removal of the mount from the engine and airframe. I've been toying with trying to buy a new mount and beefing it up prior to installing it... it's either that or I have to have the machine out of the air for a few weeks while I get the original mount repaired and upgraded.

I don't particularly like the UK SAA modification but clearly it works. The problem is it transfers the load elsewhere... which is normal... and I notice that on a friends' machine that has the UK SAA modification, the rivets are now working on that lower longeron from the firewall back to the spar. But the mount hasn't cracked again (!). I say "again" because after 1200 hours it has already had three repairs. It's a pre-1996 mount without the original gussets that were latter added by Vans.

I'm very interested to see whether the RV-14 mount lasts the distance. Vans must have identified the areas of concern and tried to beef that mount up to avoid future problems (I would hope). And then I wonder - do you go to that extent on the RV-6/7 mount?

As for repairing your one - surely there are some very competent 8130 welders in your area that could help? Saves sending it away and waiting ages for it to come back.
Click to expand...
There were actually three engine mounts, conical and two versions of the dyna-focal mount.
 
One thing I would suggest. Whatever your decision is - new or repaired engine mount- paint it white. With a dark mount, cracks are nearly invisible making it much more difficult to identify a crack before the entire tube fails.

I'd also take a really good look at the lateral angles in the firewall. I have a hard time the steel mount would fail without creating a similar problem in those aluminum angles that run across the bottom of the firewall.
 
Kyle Boatright said:
One thing I would suggest. Whatever your decision is - new or repaired engine mount- paint it white. With a dark mount, cracks are nearly invisible making it much more difficult to identify a crack before the entire tube fails.

I'd also take a really good look at the lateral angles in the firewall. I have a hard time the steel mount would fail without creating a similar problem in those aluminum angles that run across the bottom of the firewall.
Click to expand...
White is good but the factory powder coating hides cracks regardless of color. It’s white as you know.
I have had several places that might have been cracks, removed the powder coating to find nothing but poor adhesion.
 
Norman CYYJ said:
There were actually three engine mounts, conical and two versions of the dyna-focal mount.
Click to expand...
Yes, I think the dynafocal mount for my O-320 is different from the one referenced in the first post. I have a small hairline crack at a gear leg socket (quite common with mounts that have no extra gussets) that isn't propagating but have never seen one of the tubes crack or fracture (27 years, 1400hrs).
 
JonJay said:
White is good but the factory powder coating hides cracks regardless of color. It’s white as you know.
I have had several places that might have been cracks, removed the powder coating to find nothing but poor adhesion.
Click to expand...
That black paint hid any and all streaks from the crack. I don't think white powder coating would have hidden the crack for long enough to develop into a complete failure. Could be wrong.
 
Norman CYYJ said:
There were actually three engine mounts, conical and two versions of the dyna-focal mount.
Click to expand...
There was a level of sarcasim in my statement, Norman. :D Yes, there were Conical, Dynafocal 1 and Dynafocal 2 mounts available, but the cracking can happen to any of them.

JonJay - "Frustrated" is one word for it, but not the word I used when I found the cracks at the last inspection. At this stage they are very small, and located on each of the lower outboard cluster where the mount attaches to the firewall. The cracks appear to be behind the vertical tube so there is no hope of welding in-situ. I had been concentrating my visual inspection of the mount on the cluster at the top of the gear legs as this is where I'd previously seen cracks on other RV-6's. A friend came into the hangar while I was looking at the gear leg cluster and pointed to my mount and said his were cracked at the bottom like mine. And sure enough, it was. Damn.

Considering the number I've personally seen cracked; the number I've heard about being cracked via this forum or elsewhere; the addition of modfications and gussets to prevent cracking by folks all around the world, there is clearly a high incidence of cracking going on. Whether you have a machine with 1000+ hours or only 200 hours, whether your mount was manufactured in 1995 or 2008, there's a good reason to be diligent in your engine mount inspections. Which leads me to my original statement that there seems to only be two types of mounts........
 
A couple of comments on this- If the alignment of the fueslage structure and the engine mouint bolts is not near perfect this will put a continual extra stress on the mount. The mounts are TIG welded and the exact weld technique may vary even with the same welder and even during an 8 hour day. These are likely the main causes of cracking between two seemingly identical mounts.
4130 steel is very sucepptable to air hardening.
a very small portion of a weld that is air hardened may be a starting point for a failure. With TIG this results from failure to gradually back off on the heat at the termination of a weld bead and or pulling the torch away when terminating a weld instead of holding the torch in place and allowing the post flow of gas to protect the weld until it partially cools.
 
Return of experience... 1999 kit, the -6.9 had about 300 hours when I acquired it. Noticed hairline cracks on the lower side of each gear-leg trunnion on the engine mount during the pre-buy. Those were each about 25mm long, and I watched them doing nothing for the next 7 years and some 2K hours with about as many landings (not all perfect). The only thing that happened during this time was the appearance of some rust in the cracks.
Taking advantage of my recent engine replacement I removed the mount and had it NDTed locally. The cracks were right on the weldment edges, also extending to the non-visible bottom side of the mount. Had them rewelded locally, all good for now :)

rem.jpgmnt.jpg
 
Dan 57 said:
Return of experience... 1999 kit, the -6.9 had about 300 hours when I acquired it. Noticed hairline cracks on the lower side of each gear-leg trunnion on the engine mount during the pre-buy. Those were each about 25mm long, and I watched them doing nothing for the next 7 years and some 2K hours with about as many landings (not all perfect). The only thing that happened during this time was the appearance of some rust in the cracks.
Taking advantage of my recent engine replacement I removed the mount and had it NDTed locally. The cracks were right on the weldment edges, also extending to the non-visible bottom side of the mount. Had them rewelded locally, all good for now :)

View attachment 110089View attachment 110090
Click to expand...
That is the crack that can occur on RV-6 mounts that don't have gussets. It seems the crack relieves compression stress then doesn't propagate any further.
 
Sam Buchanan said:
That is the crack that can occur on RV-6 mounts that don't have gussets. It seems the crack relieves compression stress then doesn't propagate any further.
Click to expand...

Thanks Sam, but this is a -7 mount, with all them gussets. I also know that the aircraft had a hard landing (probably around 5 on the Richter scale 😅) prior to my purchasing, as I discovered during the pre-buy.
 
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