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

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


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