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

Mel 11-25-2010 06:39 AM

Quote:

Originally Posted by vernhendershott (Post 487941)
Mel, perhaps you could advise us as to how we present an aircraft for ELSA certification with this kind of known defect?
Best regards,
Vern

Unfortunately we are bound by regulations. Until Van's releases an "approved" fix, the aircraft must be presented for certification exactly per plans!

ScottSchmidt 11-25-2010 07:49 AM

Drilled Screws
 
Here is a link to McMaster Pre-Drilled bolts. What size are the bolts?

Unless something better comes out I plan on using the loctite and these SHCS with safety wire. I wish there was a way we could use a cotter pin but this should work just fine.

http://www.mcmaster.com/#socket-cap-screws/=9vesqu

Mich48041 11-25-2010 08:07 AM

Nord-Lock washer supplier
 
I see that McMaster Carr sells NordLock washers.
http://www.mcmaster.com/#nord-lock-washers/=9vf458
Joe

JBPILOT 11-25-2010 08:36 AM

Hey guys - -
 
I think it would be good for some of us to try different things, and report how they work. I just COMPLETELY Wetted my bolts threads ( all 4 ), and put them back in with the provided washers. I think getting plenty of 'blue' on the threads is important. Lets all report our results HERE. If any problems, we need to know about them. I'd like to see the alternate washers tried. I still firmly believe Loctite is the best solution. Don't over-tighten them if you use it.

John Bender

Tony_T 11-25-2010 09:11 AM

Hey John...
 
You have the most hours with Loctited screws. Couple of questions.
Which Loctite "blue" are you using, 242 or 243?
Did the screws stay tight for 100 hours until you just loosened them?
What did the break-away torque feel like? Did you try to measure it?

Sorry for being so pesky, but I am really concerned about this and trying to get as much info as possible.

Tony

JBPILOT 11-25-2010 09:19 AM

Hey Tony - -
 
When I first found it, a couple were very loose ( bottoms ). The top ones were only slightly loose. I did not measure anything. I just removed them, checked the threads inside the block, and put 'blue' ( don't have it here at home, so don't know which number ) on them, and that is it. Don't think it would make any difference which blue. Blue is 'medium' strength. I had over 100 hours on them when I found it, but have no way of knowing when they first started to loosen. I have put on maybe 75 hours since then, and all my pen marks have stayed exactly in place. Don't plan to touch them again, unless I see movement. I might go back and put the bright yellow stuff on so it has to 'break' the paint, so to speak, so I will know if there is any movement.

John Bender

Tony_T 11-25-2010 10:51 AM

Quote:

Originally Posted by ScottSchmidt (Post 488015)
Here is a link to McMaster Pre-Drilled bolts. What size are the bolts?

Unless something better comes out I plan on using the loctite and these SHCS with safety wire. I wish there was a way we could use a cotter pin but this should work just fine.

http://www.mcmaster.com/#socket-cap-screws/=9vesqu

Scott, the bolts are M10 X 30mm threaded length. There is no grip (unthreaded) portion on the shank, they are all threaded. The bolt and split washer are strongly magnetic so are not SS. They appear to be cad plated.
Since the heads sit down in a hole in the engine mount, I don't see how you could get safety wire to work.

Tony

Jetguy 11-25-2010 10:54 AM

Bolt Check updaten on our RV12!
 
We checked our Mounting bolts 2 days ago. 11/23/2010 Before removing the bolts and adding blue locktie we tried to tighten each bolt with the torque wrench. As seen from the cockpit. The 12oclock position on the bolt head would be 0 degrees. Lower Left bolt moved about ten degrees before the torque wrench clicked over. Lower right bolt moved about 5 degrees. The upper right bolt didn?t move at all. We didn?t mess with the upper left bolt. We marked and will monitor it and see if it moves. 70 hours on the Engine and airframe. We put "witness marks" on the bolts for further monitoring. We originally installed all 4 bolts per the plans with no locktite and torqued them to 26 ft-lbs with the prescribed lock nuts. We did this prior to seeing Vans Notice!

Did you use loctite or not? Not on the initial installation.
Torque specs? 26 ft-lbs
Did you install lock washers? Yes per the instructions
Engine hours when you checked them? 70hrs

PS: Do we have any doubt why those oil senders on the front of the engine are failing? Hence the Vibration thats causing these bolts to loosen up on the back of the engine.

Peterk 11-25-2010 08:58 PM

Quote:

Originally Posted by ErichKeane (Post 487961)
Since this is a problem that has happened in the past, what have the other manufacturers done about it? Have some used safety wire, or loctite, or what?

interesting that you mention that. One of the solutions by a Czech country several years ago was to place an 8mm hex socket into the 8mm hole on the 10mm bolt, tighten it to torque and then safety wire the socket piece sticking out. It is an interesting approach and allows you not to drill a hole through your mount or bolt

MartySantic 11-26-2010 10:18 AM

The safety wire gurus may want to comment here. Safety wire will prevent the bolt from coming out but will not prevent the bolt from loosening a bit. As soon as the bolt loosens a bit, you lose pre-load. Loss of pre-load leads to fretting of the thread faces. Not good. If the thread faces fret too much, the only solution then is a heli-coil. As the saying goes, nothing is perfect!


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