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  #1  
Old 05-31-2012, 08:59 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,352
Default Motor Mount Damage

Seems like most TC visits include discussion of a hose or cable routing, or how it is fastened/bracketed/clamped. Here is a fine example of why you want to be conservative. These photos are from an inspection of a Legend Cub last Saturday, but the same thing happens with an RV. And BTW, the aircraft only has 150 hours.

Throttle cable is routed just below the right rear motor mount. The crappy factory throttle cable bracket is attached to the engine with single engine stud. There is nothing (other than the clamp pressure of the single nut) to prevent rotation of the bracket on the stud.....if the installer didn't simply rotate the bracket when he tightened the nut. Bad design. It didn't help that the installer placed the cable on the wrong side of the bracket, and that the cable is a little too long. Sound familiar?

However it happened, the cable was against the backside of a motor mount tube, with predictable results:







The throttle cable's wire sheath didn't wear through, so we can probably keep it. The tube is another matter. Those cable sheath wires have eaten nice impressions into the tube wall, exact depth unknown. I'm not aware of published criteria for rating such damage, but I'm thinking it needs to come off for a welded patch.

So, when your TC suggests a particular cable/hose needs re-routed, or another adel clamp, or that you really should bite the bullet and order the correct length....well, consider it seriously.
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  #2  
Old 05-31-2012, 09:15 AM
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Walt Walt is offline
 
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 6,345
Default

Dan - Typically damage (after blend out) of less than 10% of the wall thickness is considered acceptable in "most" cases, a general rule of thumb.
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Walt Aronow, DFW, TX (52F)

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
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FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 2000+ hrs, New Titan IO-370, Bendix Mags
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  #3  
Old 06-02-2012, 08:52 AM
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marchudson marchudson is offline
 
Join Date: Feb 2006
Location: East Texas
Posts: 202
Default

Dan
Thanks for the post. Good reminder on what can happen in short order if things aren't done right.
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Houston
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