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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!

MartySantic 11-29-2010 11:13 AM

Added one more image to Gary's top shroud modification posted in this thread a few days ago. He added a lower nutplate. This nutplate along with the others have to be positioned to miss the fins.

There is a downside to his modification. To remove the cover to access the screws, the mainfold has to removed, you have to drain a bit of the coolant and the one water hose has to be removed.

JBPILOT 11-29-2010 11:29 AM

Possible different design - -
 
I like Gary's basic design. I might suggest puting a small alum plate UNDER the forward part of the patch as well as on top, and pop rivet the pieces to the patch. This could allow the front edge to be slipped over the forward piece, and use a screw similar to Gary's design at the rear. This would not require removing the coolant hose. If I have any reason to go back into mine again, I think I will do it that way to make it quick to remove the patch if desired without removing the hose and associated parts.


John Bender

jersey 11-29-2010 12:11 PM

Good Idea
 
Good idea John. Where were you last weekend. Im going to modify that piece per your suggestions next time I go in.

Marty have you done anything yet?

Gary

MartySantic 11-29-2010 01:34 PM

Quote:

Originally Posted by jersey (Post 489051)
Good idea John. Where were you last weekend. Im going to modify that piece per your suggestions next time I go in.

Marty have you done anything yet?

Gary

Have not done anything, yet. Stuck at home on home project. I like John's idea. Sounds very workable. And removes one disadvantage.

Gary, what would then have to be removed to access the one lower screw? The carb? The carb drip tray? Anything else?

Tony_T 11-29-2010 03:35 PM

Washers...
 
Received some Nord-Loc washers from McMasters today. Planning to take them to the hangar tomorrow to see if they will fit in the holes. They measure 0.65" in diameter vs. 0.633 for the furnished split washers. Your can see in this picture they are slightly larger than the bolt head. If need be they can be slightly reduced in diameter.

I am planning to use the Nord-Locs, with no Locktite, and see how they work out. This will allow putting a torque wrench on the bolts every 25 hours, like the Nord-Loced prop bolts.
Still have work to do, need to make the shroud modification, I like Gary's removeable cap, with John's mod. That will allow getting on the upper left bolt with a standard allen socket rather than a ball-end key, which I don't trust.

Tony

BigJohn 11-29-2010 04:50 PM

Quote:

Originally Posted by jersey (Post 487641)
Cut a section of the cowl out to access the upper left. Gary

Gary,

What tool/technique did you use to make that nice neat cutout?

John

Jamesey 11-29-2010 05:00 PM

Not There Yet
 
From the guys that have the problem, any sugestions for those who have not got to this stage? What would you have done during construction had you known the problem?

JBPILOT 11-29-2010 05:17 PM

Hey Jim - -
 
Add Loctite BLUE generously to the 4 bolts. Made a removable cap for that corner of the air duct. That is about it.

John Bender

Tony_T 11-29-2010 06:50 PM

Stay tuned...
 
Quote:

Originally Posted by Jamesey (Post 489143)
From the guys that have the problem, any sugestions for those who have not got to this stage? What would you have done during construction had you known the problem?

So far, there are a several unproven (and unofficial) ideas. Nothing is for sure yet, but the body of knowledge is increasing rapidly.

Tony

Peterk 11-29-2010 09:33 PM

Unfortunately
 
Quote:

Originally Posted by Jamesey (Post 489143)
From the guys that have the problem, any sugestions for those who have not got to this stage? What would you have done during construction had you known the problem?

Unfortunately you cannot do anything during construction or you are signing a fraudulent compliance statement at the end. So far, Van's has authorized changing the shroud which will be repeated soon in a revision to that page in your construction manual. These changes you read about are legal because they are made AFTER the fly-off period. With this aircraft, everything must be done as directed BEFORE the aircraft is completed. I would be very careful about making changes beforehand...you could end up with a large yard ornament.

Peterk 11-29-2010 09:37 PM

Quote:

Originally Posted by Tony_T (Post 489112)
Received some Nord-Loc washers from McMasters today. Planning to take them to the hangar tomorrow to see if they will fit in the holes. They measure 0.65" in diameter vs. 0.633 for the furnished split washers. Your can see in this picture they are slightly larger than the bolt head. If need be they can be slightly reduced in diameter.

I am planning to use the Nord-Locs, with no Locktite, and see how they work out. This will allow putting a torque wrench on the bolts every 25 hours, like the Nord-Loced prop bolts.
Still have work to do, need to make the shroud modification, I like Gary's removeable cap, with John's mod. That will allow getting on the upper left bolt with a standard allen socket rather than a ball-end key, which I don't trust.

Tony

And still with the 26# or are you upping it to 30#? Curious because I have some on the way as well. Not really worried about the increase when removed...doesn't seem to harm our prop clamp and I have taken those off several times. And re-checked them several times as well.

Tony_T 11-30-2010 05:01 PM

Quote:

Originally Posted by Peterk (Post 489246)
And still with the 26# or are you upping it to 30#? Curious because I have some on the way as well. Not really worried about the increase when removed...doesn't seem to harm our prop clamp and I have taken those off several times. And re-checked them several times as well.

The Nord-Loc site indicates that a thread lubricant helps these washers stay secure, and they reduce the dry torque by a small percentage to compensate for the lubricant on the threads. I am thinking right now that I want to use a lubricant and use 26# torque.

I found that the washers will not go easily into the holes in the motor mount so it will be necessary to reduce their diameter by about 0.015 to make them 0.635 or no bigger than the bolt head.
Here is how I am going to do it:

Chucked up in the drill press on a hardware store bolt (note it has a smaller head than the motor screws) and file and polish with emory.

Tony

JBPILOT 11-30-2010 07:31 PM

INTERESTING BOLT TESTING TODAY
 


I want to start by saying the testing results I got today are only for - MY - interest, but I am sharing in case someone else would be 'interested' in them. I am not saying they will apply perfectly in this case, but I found them interesting.

I have a friend that runs a machine shop, and he gave me a piece of 6061 alum to do my test with. I do NOT know exactly what the 912 block is made of. I felt it would give me a decent idea of what MIGHT be close to the engine block. Using oil instead of Loctite was only to keep the threads clean for more testing, but I felt it would give me a good idea of the difference between dry and lubed. I drilled the block to 11/32", and tapped it to 10M X 1.50 thread. I used a steel washer to simulate the lockwasher provided, and simulate the possible torque it creates. I used a 10M X 20M, 8.8 cap screw. I felt it was similar to the actual amount of threads in the engine block.

The results are :

DRY, as shown - 85# the torque wrench clicked solid 3 times.
At 90#, the threads started to give.

OILED, at 80#, clicked solid 3 times. ( used other side of alum block )
At 85#, the threads started to pull.

MY OPINION - I feel at 26 or 30#, we are well under stressing the bolts or threads.
MY OPINION, Loctite is the best answer for now.

John Bender

Peterk 11-30-2010 08:45 PM

Quote:

Originally Posted by Tony_T (Post 489506)
The Nord-Loc site indicates that a thread lubricant helps these washers stay secure, and they reduce the dry torque by a small percentage to compensate for the lubricant on the threads. I am thinking right now that I want to use a lubricant and use 26# torque.

I found that the washers will not go easily into the holes in the motor mount so it will be necessary to reduce their diameter by about 0.015 to make them 0.635 or no bigger than the bolt head.
Here is how I am going to do it:

Chucked up in the drill press on a hardware store bolt (note it has a smaller head than the motor screws) and file and polish with emory.

Tony

Looks good. Mine should be here shortly. Thanks for all the beta work! Like you I agree with the lubricant because of what they mentioned on their website. Can't say I was crazy about their choice though because of the low flash point of graphite. Have you chosen something else?

MartySantic 12-01-2010 08:37 AM

Quote:

Originally Posted by Peterk (Post 489557)
Looks good. Mine should be here shortly. Thanks for all the beta work! Like you I agree with the lubricant because of what they mentioned on their website. Can't say I was crazy about their choice though because of the low flash point of graphite. Have you chosen something else?

Had to re-look at the Nordlock website. They say for stainless or large diameter bolting a thread lubricant is beneficial and they list the reasons.

It is well known that a stainless bolt into a stainless body or nut is subject to galling, thus the recommendation for a lube. In our application, a coated capscrew into an aluminum casting, galling and drag is not really an issue. Same reasoning applies to the prop bolting with nordlock washers. Sensenich did not specify a lube.

Lightly oiling a bolt or using graphite, changes the k-factor. (T=k * F * D)

Peterk 12-01-2010 09:43 AM

[quote=MartySantic;489675]
It is well known that a stainless bolt into a stainless body or nut is subject to galling, thus the recommendation for a lube. In our application, a coated capscrew into an aluminum casting, galling and drag is not really an issue. Same reasoning applies to the prop bolting with nordlock washers. Sensenich did not specify a lube.

Makes sense.

Tony_T 12-01-2010 12:35 PM

Agreed
 
[quote=Peterk;489693]
Quote:

Originally Posted by MartySantic (Post 489675)
It is well known that a stainless bolt into a stainless body or nut is subject to galling, thus the recommendation for a lube. In our application, a coated capscrew into an aluminum casting, galling and drag is not really an issue. Same reasoning applies to the prop bolting with nordlock washers. Sensenich did not specify a lube.

Makes sense.

Copy, lube probably not appropriate.
I did find that I could not file the SS Nord-Locs, they seem harder than my files. I also have the coated steel washers and they are very hard too, but can be reduced in diameter with files. I have a machinst friend who probably could grind the SS ones, but am considering whether the coated steel would be better. As a side note, I bolted some test washers up in an M10 bolt and nut to see if 26-30 ft-lb would lock them up. It does. Then to undo them is interesting. There are 12 ramps in the washers, so it takes 30° of rotation before they snap. During that 30° if feels all the world like you are pushing against a spring, which you are. Takes some getting used to. I noticed the same strange feeling when I undid the Nord-loced brake bolts.

I think the Nord-Locs could be reused 3 or 4 times, but each time there is a little wear on the teeth on the outer surfaces that grip the bolt. This occurs more on loosening, not on tightening. I think I would replace them after unlocking them twice.

Tony

todehnal 12-01-2010 03:59 PM

How about a Dremel??
 
[quote=Tony_T;489739]
Quote:

Originally Posted by Peterk (Post 489693)

Copy, lube probably not appropriate.
I did find that I could not file the SS Nord-Locs, they seem harder than my files. Tony

Hey Tony! I think that a fine stone, used in a powered up handy grinder, gingerly approaching the washers that are spinning in your jig, would do the trick. It may be worth a try.

Tom

dick seiders 12-01-2010 04:06 PM

Posted this on the "Notice" thread, but felt it is gemain to this one as well.
Just catching up. Did not get to do my planned check on my engine bolts this past weekend as a kitchen floor project was assigned a higher priority by a girl I married a long time ago. I did get to talk with Lockwood's top Tech guy tho and his counsel is to use the blue Loctite AND keep the torque at 312 inch lbs. He feels the lower the torque that holds in an aluminum case , the better. Since some of you have reported the successful holding with the blue Loctite that makes sense. I know some have gone to the 360 in lbs, but not all unless I missed it in reading the posts. He also felt the lubricity provide by the Loctite would cause little if any additional torque on the bolts. Regarding the Nordloks he felt they were not necessary as the Loctite should do the job. I will check my bolts at the earliest opportunity (and before flying) and will provide results. I would appreciate any comments this information generates. Thanks.
Dick Seiders

dick seiders 12-01-2010 04:07 PM

ditto for this post today.
Received an e mail from Rotax Tech today stating that after his discussing the torque issue with Van's today the 312 in.lbs was in error per Vans so Rotax says go with the 360 in.lbs. per Rotax specs. He did not mention the blue Loctite, but in view of his earlier statement I would presume the blue would be used in conjunction with the 360 in.lbs. torque level.
Dick Seiders

Geico266 12-01-2010 04:51 PM

Tony, You are on the right path to reduce the OD of the Norlock washers. Take the mandrel set up you have in the drill press and put it in a hand drill. With the drill spinning in the opposite direction of the bench grinder gently touch the washers on a spinning wheel. Dress the grinding wheel of the bench grinder so the wheel is clean and true. Go slow and square to the wheel and you will achieve a very nice result. Use the spinning 3M wheel to debur up the edges.

Let us know how it turns out.

rschy 12-01-2010 06:53 PM

If anyone has any doubt about how Rotax feels about Loctite check out the maintenance manual 05-00-00 page 7;)

vernhendershott 12-01-2010 07:24 PM

Got to do the check on 120186 today, the upper left and lower left were tight, the upper right required about 1/8 turn to come back to full torque and the lower right was missing.

Found that it was necessary to remove the right drip pan to get a proper tool to the upper right bolt.

The plan is Loctite 242 and return to service. Then watch every 25 hours for at least 100 hours.

Best regards,
Vern

Mich48041 12-01-2010 07:34 PM

How many hours?
 
Vern,
How many hours are on 120186?
Thanks,
Joe

clucier 12-01-2010 07:41 PM

OK missing is not something I want to hear at all regarding an engine mount bolt. How many hours?

Quote:

Originally Posted by vernhendershott (Post 489879)
Got to do the check on 120186 today, the upper left and lower left were tight, the upper right required about 1/8 turn to come back to full torque and the lower right was missing.

Found that it was necessary to remove the right drip pan to get a proper tool to the upper right bolt.

The plan is Loctite 242 and return to service. Then watch every 25 hours for at least 100 hours.

Best regards,
Vern


Brantel 12-01-2010 07:56 PM

Quote:

Originally Posted by vernhendershott (Post 489879)
snip....lower right was missing...snip

Best regards,
Vern

:eek: Wow! Keep finding this stuff and we may see our first AD issued against Van's...

I wish you guys the best of luck finding a fix for this one!

Falling out is really bad but so is a loose bolt in there wallowing out the hole. That sure is an expensive case to have to replace or repair...As well designed as the rest of the RV12 seems to be, this shocks me that this was put out there this way.

DonFromTX 12-01-2010 07:58 PM

Think of the poor slobs flying around in 12's that are NOT on this forum!

Geico266 12-01-2010 08:02 PM

Quote:

Originally Posted by DonFromTX (Post 489896)
Think of the poor slobs flying around in 12's that are NOT on this forum!

If you know of any please make every effort to contact them immediately!

MartySantic 12-01-2010 08:08 PM

Quote:

Originally Posted by rschy (Post 489870)
If anyone has any doubt about how Rotax feels about Loctite check out the maintenance manual 05-00-00 page 7;)

I reviewed the ROTAX Line Maintenance page. What are you trying to tell us?? It is merely a list of consumables??? The manual SPECIFICALLY tells us when and when not to use loctite.

In the case of the engine mount bolting, all of the USA repair centers seem to be using blue loctite for this bolting even tho the line maintenance manual does NOT suggest it.

vernhendershott 12-01-2010 08:25 PM

Sorry I should have indicated that 120186 has just under 40 hours total time and the 25 hour inspection was done by Lockwood, they did not check the upper left as the shroud was not moved, they may have checked the others or not.

Best regards,
Vern


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