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03-31-2018, 12:13 PM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Engine mount wrong?
The upper corners of my engine mount seem wrong. There is 1/2 ID tube where I think there should be 3/8 so the bolt wallows around. Also an AN6-24 is too short. Any ideas? I asked Vans already but quicker answers here!!!

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Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
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03-31-2018, 12:20 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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It is purposely over sized.
The only hole diam. that matters structurally is the one in the flange that mates with the firewall.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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03-31-2018, 01:14 PM
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Join Date: May 2014
Location: Seattle
Posts: 323
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hard to tell with the angle, but it looks like my (14A) upper left tube might be shorter than the one in your pic, but upper left and right bolts are AN6-26A on the taildragger

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RV-14A flying 410 hrs
Last edited by Jake14 : 03-31-2018 at 01:29 PM.
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03-31-2018, 01:31 PM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Scott, is there some manuf variability in the depth of that mount tube? My right and left upper corners both need a 25 or 26. The plans are usually dead on. I for sure have the right bolt sized it on the size chart.
__________________
Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
Last edited by JDA_BTR : 03-31-2018 at 01:34 PM.
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04-02-2018, 12:30 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by JDA_BTR
Scott, is there some manuf variability in the depth of that mount tube? My right and left upper corners both need a 25 or 26. The plans are usually dead on. I for sure have the right bolt sized it on the size chart.
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The production drawing shows that the upper two bushings should be 1.25" long (beyond the face of the flange washer), and the lower 4 bushings should be 1.0" long.
I have not heard of any other complaints about the specified bolts being too short.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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04-04-2018, 02:56 PM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Measured my upper mount bushings and mine measure just shy of 1.5 inches past the big washer or 1-5/8 from the firewall. That?s an extra 1/4 too long. So do I just upsize the bolt length or get another mount?
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Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
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04-10-2018, 06:20 PM
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Join Date: Dec 2013
Location: Baton Rouge, LA
Posts: 1,055
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Final answer on this was the tube diameter is right but my tube is 1/4 too long. Up two bolt sizes and carry on I was told.
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Ser 104142, RV-14A flying - N1463 
Ser 83825, RV-8 building - N8638? 
USN Ret, Urologist, AME, Repeat Offender
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04-10-2018, 06:42 PM
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Join Date: May 2014
Location: Seattle
Posts: 323
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maybe someone welded a taildragger tube on a tri-gear mount. taildragger upper tubes are longer for some reason
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RV-14A flying 410 hrs
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08-19-2018, 05:05 PM
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Join Date: Nov 2012
Location: Midland, mi
Posts: 962
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How much of the bolt should stick through the firewall? What is the minimum amount of threads that should show on the end of the bolt after torquing down the nuts?
My upper bolts seem to too short like stated above. I have about 1 thread showing before torquing down on the bolts.
The lower bolt will have lots of exposed thread.
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Ken Stockman
Midland, MI
EAA Chapter 1093 member
FaceBook Page: Ken's RV-14
RV-14a (serial number 140073)
N73XP
Plane at hangar and the wings ON.
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08-19-2018, 05:12 PM
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Join Date: Jun 2018
Location: Colorado
Posts: 168
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Quote:
Originally Posted by Stockmanreef
How much of the bolt should stick through the firewall? What is the minimum amount of threads that should show on the end of the bolt after torquing down the nuts?
My upper bolts seem to too short like stated above. I have about 1 thread showing before torquing down on the bolts.
The lower bolt will have lots of exposed thread.
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Page 5-18:
"A common rule of thumb for evaluating whether an installed bolt is the proper length has always been that up to three thick washers are allowed (if more than three are needed the next shorter bolt should be used), and that at least one but no more than three full threads of the fastener are to be showing beyond the nut. This rule of thumb works for the AN365 nuts that have been commonly used on RVs for years.
Some of the newer RV kits use the all metal MS21042 self locking nut. The long standing rule of thumb will not work for these nuts because they are shorter in height than the AN365 nut. For these nuts, modify the rule of thumb to ?at least three, but not more than five threads showing.? This rule of thumb will still allow for meeting the 'maximum use of three washers' rule.
You may have to educate any technical councilors or airworthiness inspectors that perform inspections on your project. Some
inspectors are not familiar with these smaller sized nuts."
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