Suspicious Crack in Engine Mount Powder Coat

[rtlongdon]

I'm working my way through my CI and I removed the ignition coil packs to replace plug wires and get a really good look at the underside of the coils (I did find some chafing and indication of arcing underneath, so I'll repair that).

Aside from the coils, it's a great opportunity to get a really good look at the top right engine mount attach. I noticed this very small crack in the powder coating on the top of the mount.

My plan is to strip the powder coat back and verify what I'm seeing, but interested in any more experienced eyes weighing in on what your gut feel would be if you saw this. If nothing else we can start a betting pool. Of course, I'll report back what I find.

Thanks!

 

[Dan 57]

Your plan certainly is good. Though the crack in the coating doesn't seem reddish, there could still be a crack in the mount itself... underlying corrosion can crack a lawyer of powder coating.

Difficult to say any more until the mount is exposed, though I'm only acquainted with the -12, let's hope someone with a similar experience on type will respond.

 

[Piper J3]

It looks like you have an older legacy 12 with first version of engine mount that doesn’t have strengthening gussets at the engine attach points. See photo below that shows gusset. This is actually early gusset – latest version has gusset welded on inside surface of tubing for better visual inspection of tubing when bolted to engine.

Every cracked engine mount I have seen has location of cracked tube outside of weld zone. Must cracks have been just outside of the weld which some people think indicates thermal stress induced during the weld process. TIG / MIG welding does not uniformly heat the substrate, nor allow controlled post-cooling. Gas welding is much better choice for 4130 Chromoly tubing.

 

[lr172]

Notice the cracked coating to the left, which is almost certainly not a crack in metal. This happens some times, especially if a bit of oxidation was left before coating. The crack in question "appears" to be over the weld bead and cracks almost never from there. Instead, they form just a bit out from the bead in the parent metal in an area called the HAZ - heat affected zone. Coating is thick in that area, so difficult to tell from the pic exactly ehere it is relative to the bead.

You can post a pic after you scrape off some coating for a better look. No need to worry until you can see what is under it. My initial guess is this is not a crack, but totally a guess and coating removal is absolutely in order here to get a look at the metal.

 

[David Paule]

Worth mentioning is that there's a decent alternative to powder coating engine mounts: cad plate them. The plating is very thin and won't hide cracks. I did this to the mount on my RV-3B project.

Dave

 

[Mikeyb]

It looks like you have an older legacy 12 with first version of engine mount that doesn’t have strengthening gussets at the engine attach points. See photo below that shows gusset. This is actually early gusset – latest version has gusset welded on inside surface of tubing for better visual inspection of tubing when bolted to engine.

Every cracked engine mount I have seen has location of cracked tube outside of weld zone. Must cracks have been just outside of the weld which some people think indicates thermal stress induced during the weld process. TIG / MIG welding does not uniformly heat the substrate, nor allow controlled post-cooling. Gas welding is much better choice for 4130 Chromoly tubing.

It looks like you have an older legacy 12 with first version of engine mount that doesn’t have strengthening gussets at the engine attach points. See photo below that shows gusset. This is actually early gusset – latest version has gusset welded on inside surface of tubing for better visual inspection of tubing when bolted to engine.

Every cracked engine mount I have seen has location of cracked tube outside of weld zone. Must cracks have been just outside of the weld which some people think indicates thermal stress induced during the weld process. TIG / MIG welding does not uniformly heat the substrate, nor allow controlled post-cooling. Gas welding is much better choice for 4130 Chromoly tubing.

What are you showing in the photo? I see sealant slopped on a tube?

 

[rtlongdon]

Thanks for all the replies and insights. I'll remove the coating in the next day or so and let you know what I find.

It looks like you have an older legacy 12 with first version of engine mount that doesn’t have strengthening gussets at the engine attach points. See photo below that shows gusset. This is actually early gusset – latest version has gusset welded on inside surface of tubing for better visual inspection of tubing when bolted to engine.

Every cracked engine mount I have seen has location of cracked tube outside of weld zone. Must cracks have been just outside of the weld which some people think indicates thermal stress induced during the weld process. TIG / MIG welding does not uniformly heat the substrate, nor allow controlled post-cooling. Gas welding is much better choice for 4130 Chromoly tubing.

Plane is a 2013 kit, finished in 2015. You show a photo of a bottom mount gusset. Mine are gussetted on the bottoms like that. The top mounts, which is the one I'm reviewing, doesn't have a gusset.

 

[rtlongdon]

Worth mentioning is that there's a decent alternative to powder coating engine mounts: cad plate them. The plating is very thin and won't hide cracks. I did this to the mount on my RV-3B project.

Dave

In the event I have to pull it, a different finish option is on the table. I'm not a huge fan of powder for engine mounts. Thanks for floating that idea.