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Engine Motor Mount Inspection

Posted By:
Michael Crowder
Homebuilder or Craftsman
#1 Posted: 4/9/2010 10:02:34

I'm wondering what the acceptable practices are for routine checking of a motor mount for cracks.  First would be a good visual inspection with a magnifying glass as an aid.  I thought a penetrating die inspection would be useful, but they all want the paint removed for the die to penetrate into the crack.

So, how is everyone doing their engine mount inspections each year during your conditional inspection?



Michael Crowder Sonex N293SX TriGear, Dual-Controls, Jabiru 3300
Joanne Palmer
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
#2 Posted: 4/9/2010 10:19:20



There are four "technical" methods of detecting cracks, with the fifth one being a visual inspection.  The four are Magnetic Particle, Dye Penetrant, Eddy Currrent and ultrasound.  Ultrasound  and eddy current CAN be used with the paint on but better results will be obtained with the paint off.  Dy penetrant and mag particle need the paint reomoved.  You'll need the paint removed anyway to affect repairs so if you have a suspect area from a visual inspection, you can remove the paint in that area and inspect with Dye penetrant.  Or just remove the paint all together and then penetrant and repair the whole thing.


Michael Glasgow
Homebuilder or Craftsman
#3 Posted: 4/10/2010 09:13:27

The aircraft grade chemical paint remover is what you would want to use to remove paint.  Some of the non-aircraft chemicals can change the composition of the alloys in the metal.  Abrasive grit blasting can heat the metal, and cause a change in the strength.  If the welds were done by a competent welder, and the engine/prop combination is properly balanced, the engine mounts should be able to go close to the recommended TBO of the engine without repair or replacement.    The "Lord" mounts (or whatever brand are there) should last five to ten years before replacement is needed.  A very thorough and close visual inspection might be adequate if everything is aircraft grade.  I would probably recommend stripping the paint, and using flourescent dye penetrant if there is ANY suspicion AT ALL of cracks.  If the powerplant falls off in flight, the CG generally gets altered too much for the aircraft to remain in flight.  The risk to the occupants of the aircraft, as well as to people on the ground is not worth trying to save some time, if there is the LEAST AMOUNT OF DOUBT about the integrity of the engine mounts.  There are a lot of variables that can affect the integrity of the engine mounts.  As we used to say when skydiving, "when in doubt, get it out."

Long flights, smooth air, and soft landings,