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Engine mount crack?

thiggins

Well Known Member
In helping a friend complete his annual condition inspection we found what looks and feels like a tiny crack on the bottom port side of the engine mount.
I can catch it with my fingernail (barely). Hopefully the quality is good enough. The “crack” is by the weld, the streak higher on the tube is dirt.

Could this just be the powder coat?

What do we think?
 

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If you remove the paint use paint stripper sparingly, if you sand the paint you may fill in the crack and obscure it, then get dye penetrate and developer, and apply per instructions, from what I see it very well could be a crack, especially in the weld area...
 
I would scrape off the paint with a knife or razor blade to check. Not a logical place for a crack. The most likely place for a crack in that area would be in the HAZ (heat affected zone) that would extend about 1/4 - 3/8" from the weld. If something in that area were to crack, it is most likely in the HAZ, as that area is more brittle. That said, a defect in the tube would also support a crack.

My money is on just the paint that cracked. Powder coat has much less elasticity than paint.

EDIT: My apologies, I was looking at the long crack that I now see you said was dirt. The small crack by the weld is exactly the spot that is most vulnerable (intersection of weld deposit and HAZ). It is likely that is a crack in the steel and not just the paint. While I don't know the 12, that area appears to be in compression and that causes the most stress on welded joints; Just like we see in the side by side, steps at the lower weld.

Larry
 
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Cracks can, and do, happen outside Heat Affected Zone.

I have proof...
-
 

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The indication im looking at does appear to be in the HAZ ( heat affected zone) of that weld I would clean up powder coat and dye penetrate test. Very Common place for weld cracks under load.
 
Just a voice of support if you have a crack... I had cracks in my RV-6 engine mount after 1400 hrs some of it on pretty rough "landing areas". Removal, stripping, welding (including reinforcing gussets from Vans), re-powder coating and engine back on the plane was not an easy task but I did it and flying and hardly remember the pain of all that. Be VERY clear with whoever strips & re-coats it, not to bead blast or paint inside any tubes where bolts / landing gear / etc. go.
 
Looks like a crack to me. Everything nice and clean - how many hours on airplane?

It has 570 hours on it, very clean and in a hangar. It belongs to a CFI that built it and babies it…. oh boy.

:eek::eek:

Has anyone elected to replace the mount with new (and improved) engine mount offered by Vans @ approx $350 for the mount plus 7 or 8 hours labor to change it out?
(Or is that a new nose gear leg?)

Is this a good option?

Thanks.
 
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Has anyone elected to replace the mount with new (and improved) engine mount offered by Vans @ approx $350 for the mount plus 7 or 8 hours labor to change it out?

I think you need to add a "1" in front of the $350. When I discovered crack in my engine mount back in March, I researched new mount from Van’s. Cost was something like $1400 and several months delay shipping. I elected to repair with TIG weld 4140 chromoly sleave.
 
It has 570 hours on it, very clean and in a hangar. It belongs to a CFI that built it and babies it…. oh boy.

:eek::eek:

Has anyone elected to replace the mount with new (and improved) engine mount offered by Vans @ approx $350 for the mount plus 7 or 8 hours labor to change it out?
(Or is that a new nose gear leg?)

Is this a good option?

Thanks.


I wouldn’t panic yet. Do the dye penetration testing and then you can work with facts not opinions.

Oliver
 
that area appears to be in compression and that causes the most stress on welded joints

Interesting. I have no welding background, but I would have guessed that compression would be the least stressed loading direction. I tried the googler for tension vs compression of welded joints but all I could find was tension vs shear. Do you have any references you could share? Always looking to learn!
 
Generally speaking, cracks do not grow in an area of pure compression. They need tension or shear or bending.

Unfortunately, with welded tube structures, there is often a combination of all these at the welded joints. And add in vibration and reversed loads, and the bottom line is - inspect well and often.

Dave
 
Interesting. I have no welding background, but I would have guessed that compression would be the least stressed loading direction. I tried the googler for tension vs compression of welded joints but all I could find was tension vs shear. Do you have any references you could share? Always looking to learn!

The early RV-6 engine mounts are developing cracks that are compression cracks where the gear legs mount to the lower engine mount. There is an RV-7 reinforcement used to fix this issue.
 
Generally speaking, cracks do not grow in an area of pure compression. They need tension or shear or bending.

Unfortunately, with welded tube structures, there is often a combination of all these at the welded joints. And add in vibration and reversed loads, and the bottom line is - inspect well and often.

Dave

Yup, cyclic/dynamic loading will stress the entire structure to varying degrees, possibly leading to a fatigue crack, even in an area in compression statically. I just don't understand the statement that a welded joint is weaker in such an area. :confused:
 
I would do a dye penetrant test with the powder coat on. If it showed an indication I would carefully remove the powder coat layer by layer with a moto-tool and do another test after polishing the chromalloy with a Scotch Brite pad. In the nuke world we used to polish out surface indications in much more critical applications. As long as you are just polishing and not grinding there shouldn’t be an issue of wall thinning.
 
Your judgment may allow . . . . .

I get chills for the work involved, but (flamesuit on) I think I would dull the edge of a small chisel and carefully strike parallel but close to the crack to see if the paint will chip off. If so, do the other side and check for the crack. Just DON'T strike hard enough to hit the steel, just enough to see if it will chip off the paint.

Alternate tools should also be considered - like a rounded tip/dulled center punch.

If successful, and there is no metal crack then touch-up paint can restore protection.
 
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