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-   -   RV-12: Engine Mounting Cap Screws Inspection (https://vansairforce.net/community/showthread.php?t=65020)

Captain Cowboy 10-31-2013 07:55 AM

Engine Cap Screw inspection
 
In doing my conditional, 10/30/2013, found upper right engine mount cap screw totally out of hole and wedged against engine support, 60 hours total on eng/frame. Will check othes soon, aircraft grounded immediately!!!! Every flying 12 needs to be looked at now before a more serious problem results. There needs to be a Service Bulletin issued NOW that applies to all flying 12s with Rotax/Vans ELSA combination aircraft! Additionally, an Engineering permanent solution needs to be completed and disseminated to all 12 owners!!!!!

JBPILOT 10-31-2013 07:59 AM

Hey Doug - -
 
I am sure you did not use locktite blue. If you use 'blue' and 30#, you will NOT have another problem. Put torque paste on them, and NEVER touch them again. JUST LOOK at torque seal.

Captain Cowboy 10-31-2013 08:16 AM

Will do John, I also think that an SB with recurring compliance needs issued to educate those that have not had any problems yet but may in the future! Thanks

rvbuilder2002 10-31-2013 08:56 AM

Quote:

Originally Posted by Captain Cowboy (Post 821593)
Will do John, I also think that an SB with recurring compliance needs issued to educate those that have not had any problems yet but may in the future! Thanks

Checking the torque of these fasteners is included in the 100 hr inspection check list, so they should be getting checked during every engine inspection. On new engine installations, a 25 hr inspection is prescribed. The 25 hr inspection uses the exact same check list as the 100 hr, so the engine attach bolts should be getting checked at that time also.

Because of the above inspection intervals, a SB is not necessary.,..

It has now been more than 2 years since this problem originally surfaced.

A couple of details were changed that resolved the issue -
1. Corrected the torque value for the four bolts to 30 ft lbs (incorrectly spec.ed at 26 ft lbs)
2. Deleted powdercoat from the engine mount where it contacted the engine and fasteners (possible torque value drop off because of compression of the powdercoat).

There is now more than 280 RV-12's flying and yours is the first loose bolt issue I have heard of during that 2 year period.
Two years ago, some owners/builders chose to deviate from the recommended install procedure, and also used thread locker and/or locking washers.
The major majority of completions within the past 2 years have probably used the recommended installation, with no problems detected.

rvbuilder2002 10-31-2013 08:59 AM

Quote:

Originally Posted by JBPILOT (Post 821586)
I am sure you did not use locktite blue. If you use 'blue' and 30#, you will NOT have another problem. Put torque paste on them, and NEVER touch them again. JUST LOOK at torque seal.

Undisturbed torque seal is not a reliable indicator that a bolt is still fully torqued. It only indicates whether the fastener has rotated. The torque value (stretch load) of a bolt can drop off without it rotating.

JBPILOT 10-31-2013 01:10 PM

Scott - -
 
respect your statements, but until someone who has used 'blue' & 30# and reports a problem, I will stay with my method. To me it is extra piece of mind. If the bolt doesn't move, and 30# of original torque, I'm satisfied it won't be a problem. If anyone EVER has a problem and has NOT touched them after my method, I would certainly like to hear from them, and hope they post it.

Captain Cowboy 10-31-2013 04:26 PM

Scott and John, I don't just want piece of mind when we fly our 12s, I want a totally 100% safe and reliable aircraft that has the best engineering applied to its design and maintenance. That is not the case with these bolts that can completely back out in less than a year from the previous conditional and after 45 flying hours since our last conditional in Oct 2012. There has to be a better solution than adding 4 more pounds of torque and some blue loctite. We did everything according to ELSA build specs and inspections and still had the upper cap screw back out completely! It is shear luck that I found the screw still on the aircraft. The last thing we need is a hull loss because of these cap screws moving any amount. It is obvious to me that this problem has been an ongoing concern for multiple years and it NOW needs FIXED!!!!

DHeal 10-31-2013 05:01 PM

Sorry, but there never has been and never will be a "totally 100% safe and reliable aircraft". Only the politicians promise you that.

rvbuilder2002 10-31-2013 05:35 PM

Quote:

Originally Posted by Captain Cowboy (Post 821787)
Scott and John, I don't just want piece of mind when we fly our 12s, I want a totally 100% safe and reliable aircraft that has the best engineering applied to its design and maintenance. That is not the case with these bolts that can completely back out in less than a year from the previous conditional and after 45 flying hours since our last conditional in Oct 2012. There has to be a better solution than adding 4 more pounds of torque and some blue loctite. We did everything according to ELSA build specs and inspections and still had the upper cap screw back out completely! It is shear luck that I found the screw still on the aircraft. The last thing we need is a hull loss because of these cap screws moving any amount. It is obvious to me that this problem has been an ongoing concern for multiple years and it NOW needs FIXED!!!!

Doug,
As I already mentioned, yours is the first instance in two years I have heard of.
I would need a lot more information than you have given up to this point, to comment on your case.

Reread my other post (#184).
Since implementing the listed changes ~ 2 years ago, I am unaware of any instances of loose bolts. Without more information, all I can assume is there is some detail specific to your installation that caused them to loosen.

You say 45 hrs since the last conditional (proper term is condition inspection BTW). When you did that inspection, did it include verifying that the 4 bolts were properly torqued to 30 ft lbs (as prescribed in the Rotax inspection check list)?

Regarding your comment of wanting something better than 4 more pounds of torque - in the context of properly installed threaded fasteners, 4 ft pounds can make a big difference in obtaining proper stretch and preload on a fastener such as this. Many were found loose when the incorrect torque value was being used... as already mentioned, I have heard of none (until yours) since the correct torque value has been used. BTW, the 30 ft pound value is a specification from Rotax. It can be found in the illustrated parts manual.

Captain Cowboy 11-01-2013 11:43 PM

I must correct my original post, it was the lower right cap screw that came completely out! I just read every post in this forum on this subject which I should have done before posting my comments! I was totally unaware of all the problems others had, previously, with this subject and their subsequent actions. After reading all of these and consulting with a friend who is an Aero Engineer about why these bolts/cap screws move/back out, I have come to the realization that nothing will totally guarantee that these bolts do not vibrate out short of engineering a different eng mount that mechanically locks them in place after installation! I also realize that this is a costly correction for Vans, Rotax, or whoever is responsible for this mod. It is true that we in the field will ultimately solve it before all the engineers get around to it, which apparently has already happened using loctite, increasing torque, using nordlocks or other combinations thereto. I just stumbled onto this problem of mine because of reading VAF posts and looking at our aircraft!!! I never received any info from Vans or Rotax about loose cap screws or shroud mods that would have clued me into this problem, but I should have!!! As others before me have solved this Experimental problem, i will also.


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