Van's Air Force
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- Thread starter DeltaRomeo
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MartySantic
Well Known Member
Thanks!! Addresses the cooling shroud modification to allow the required inspection. DOES NOT address any PREVENTATIVE measure!! Van's has reports that the capscrews are coming loose between the ROTAX 100 hr inspection intervals. Waiting patiently.
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Cooling shroud modification
I agree; this is very incomplete because it doesn't address the crux of the problem, namely, that the screws come loose.
I am going to use Lock Tite and wonder if different washers might also be a good idea since the present ones don't seem to work.
I agree; this is very incomplete because it doesn't address the crux of the problem, namely, that the screws come loose.
I am going to use Lock Tite and wonder if different washers might also be a good idea since the present ones don't seem to work.
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David Paule
Well Known Member
Is it possible to find suitable self-locking bolts? That is, bolts with a self-locking insert built into the threads.
Too bad there's no way to safety-wire the heads. Or is there? Could a small hole be drilled near the edge of the mount tube and then use drilled-head bolts?
Too bad there's no way to safety-wire the heads. Or is there? Could a small hole be drilled near the edge of the mount tube and then use drilled-head bolts?
MartySantic
Well Known Member
Please be aware and give consideration to the following before blue Loctite is used on the capscrews. I am not for or against the use of loctite. Just want to present the facts.
The torque as listed in the RV-12 plans and the ROTAX documentation assumes dry threads. When the threads are lubricated, (as with a light oil or loctite), the torque at the head of the capscrew must be decreased to get the same clamping action force at the thread faces. (If the forces become too great at the threads, you will pull the threads from the case or strip the threads on the capscrew, or both). Maybe someone knows how to perform a formal torquing calculation!!
Once loctite is applied, capscrew tightness must be checked via other means. You do not want to break the loctite bond. If broken, the loctite is useless. Torque-seal would be an alternative.
Also, note the torque as listed in the RV-12 plans is NOT the same as the torque value as listed in the ROTAX parts manual. (310 in-lbs vs. 360 in-lbs). The .pdf file tells us to follow the ROTAX documentation. I do not know how close 360 in-lbs is to the yield point of the bolt and case material. If close to the yield point, loctite most certainly has to be accounted for. A good example are the AN5 prop bolts. Van's on plan page 05-10, tells us to torque an AN5 to 100-140 in-lbs. Sensenich tells us to torque the same AN5 to upwards of 265 in-lbs. The Sensenich number, based on a back of the hand calculation is near 100% of yield. OK, but little room for error.
It is my hope, Van's is working on something preventative. Now that Van's has issued the bulletin, Scott may have the latitude to comment on whether Van's is continuing to work on preventative measures. Or tell us Van's considers this issue closed.
What bothers me the most is there has been no official notification by Van's to the RV-12 owners. If an RV-12 is flying and is not monitoring this website, he/she could be flying with 2 or less engine mounting capscrews. NOT GOOD! Some have found this to be the case even though, they have meticulously followed all of the RV-12 and ROTAX periodic engine inspection requirements. A simple e-mail would cure this. IS that too much to expect even though we are now experimental?
The torque as listed in the RV-12 plans and the ROTAX documentation assumes dry threads. When the threads are lubricated, (as with a light oil or loctite), the torque at the head of the capscrew must be decreased to get the same clamping action force at the thread faces. (If the forces become too great at the threads, you will pull the threads from the case or strip the threads on the capscrew, or both). Maybe someone knows how to perform a formal torquing calculation!!
Once loctite is applied, capscrew tightness must be checked via other means. You do not want to break the loctite bond. If broken, the loctite is useless. Torque-seal would be an alternative.
Also, note the torque as listed in the RV-12 plans is NOT the same as the torque value as listed in the ROTAX parts manual. (310 in-lbs vs. 360 in-lbs). The .pdf file tells us to follow the ROTAX documentation. I do not know how close 360 in-lbs is to the yield point of the bolt and case material. If close to the yield point, loctite most certainly has to be accounted for. A good example are the AN5 prop bolts. Van's on plan page 05-10, tells us to torque an AN5 to 100-140 in-lbs. Sensenich tells us to torque the same AN5 to upwards of 265 in-lbs. The Sensenich number, based on a back of the hand calculation is near 100% of yield. OK, but little room for error.
It is my hope, Van's is working on something preventative. Now that Van's has issued the bulletin, Scott may have the latitude to comment on whether Van's is continuing to work on preventative measures. Or tell us Van's considers this issue closed.
What bothers me the most is there has been no official notification by Van's to the RV-12 owners. If an RV-12 is flying and is not monitoring this website, he/she could be flying with 2 or less engine mounting capscrews. NOT GOOD! Some have found this to be the case even though, they have meticulously followed all of the RV-12 and ROTAX periodic engine inspection requirements. A simple e-mail would cure this. IS that too much to expect even though we are now experimental?
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Marty, I know this thread is about the engine bolts, but that's a big difference in torque values. What number did you/others use for the prop bolts?
MartySantic
Well Known Member
The Sensenich prop manual tells us to torque all of the AN5 prop bolts on the RV12 to 240-265 in-lbs. The Sensenich number takes precedence over any general suggestion by Van's.
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Safety wire is not the solution
Safety wire will keep a bolt from coming out, but it will not prevent the bolt from loosening slightly. Once a bolt loosens slightly, there will be excessive wear.
I like the loctite idea (once proper torque is determined) or Nordlock washers like on the propeller. What if both methods were used?
Joe
http://www.nord-lock.com/default.asp?url=2.16.37
Safety wire will keep a bolt from coming out, but it will not prevent the bolt from loosening slightly. Once a bolt loosens slightly, there will be excessive wear.
I like the loctite idea (once proper torque is determined) or Nordlock washers like on the propeller. What if both methods were used?
Joe
http://www.nord-lock.com/default.asp?url=2.16.37
Cooling shroud modification not too bad
I happened to be performing my 25 hour inspection and oil change and given that I had the cowling off, I went ahead and performed the cooling shroud modification this afternoon shortly after it was posted on Van's website. It was not too difficult to do- will see how the fiberglass patch turned out once it cures and I peel off the plastic wrap. Pretty tight quarters in which to try and do good fiberglass work! Took about 1 1/2 hours. The modification will provide more than adequate access for a ball-end allen wrench.
As an aside, I have checked my lower two mount bolts and they were still tight. Will check the upper two after the patch dries. But then, I only have 21 hours on mine thus far.
Jeff
I happened to be performing my 25 hour inspection and oil change and given that I had the cowling off, I went ahead and performed the cooling shroud modification this afternoon shortly after it was posted on Van's website. It was not too difficult to do- will see how the fiberglass patch turned out once it cures and I peel off the plastic wrap. Pretty tight quarters in which to try and do good fiberglass work! Took about 1 1/2 hours. The modification will provide more than adequate access for a ball-end allen wrench.
As an aside, I have checked my lower two mount bolts and they were still tight. Will check the upper two after the patch dries. But then, I only have 21 hours on mine thus far.
Jeff
What is the solution?
Joe,
Actually, Nordlock recommends a lubricant to maximize the strength of their locking system. http://www.nord-lock.com/default.asp?url=357.16.37
As I read Marty's links and the Nordlock site I begin to believe this is a complex science (and my arse may depend on it
).
If Loctite is used then you can't check torque without breaking the Loctite, although if you have witness marks, that may suffice. If fretting and wear occurs between the steel mount and the aluminum engine case, the bolts may lose clamping force even if Loctited. Maybe I am over thinking this.
Also, there are several grades of Loctite. Which one is best for this steel to aluminum critical joint?
With the Nordlock system, you can check torque like you do on the propeller.
If I had to rely on my own judgement, I don't know which method I would use and so have not yet torqued up my engine bolts.
I am still hoping for an engineered solution from Van's.
Tony
Joe,
Actually, Nordlock recommends a lubricant to maximize the strength of their locking system. http://www.nord-lock.com/default.asp?url=357.16.37
As I read Marty's links and the Nordlock site I begin to believe this is a complex science (and my arse may depend on it
). If Loctite is used then you can't check torque without breaking the Loctite, although if you have witness marks, that may suffice. If fretting and wear occurs between the steel mount and the aluminum engine case, the bolts may lose clamping force even if Loctited. Maybe I am over thinking this.
Also, there are several grades of Loctite. Which one is best for this steel to aluminum critical joint?
With the Nordlock system, you can check torque like you do on the propeller.
If I had to rely on my own judgement, I don't know which method I would use and so have not yet torqued up my engine bolts.
I am still hoping for an engineered solution from Van's.
Tony
No room to remove bolt?
From looking at the pictures, it seems that the cooling shroud modification allows room to insert the allen wrench into the bolt. But can the bolt be removed? Without removing the bolt and applying loctite or Nordlock washers, the problem still exists. Won't we still be concerned about the engine falling off on long trip around the country or longer? Or do I have it wrong?
Joe
From looking at the pictures, it seems that the cooling shroud modification allows room to insert the allen wrench into the bolt. But can the bolt be removed? Without removing the bolt and applying loctite or Nordlock washers, the problem still exists. Won't we still be concerned about the engine falling off on long trip around the country or longer? Or do I have it wrong?
Joe
It looks like you have it right. Also, I am not too sure about those ball head allen keys. They do not appear to give full strength. If you strip the allen slot in that bolt it would present another nasty problem to deal with. Gary's nifty mod in this thread will let you take out the screw if you need to; and, you can use a regular allen socket.
If you did decide to do the air duct mod per Van's plan then you will need some epoxy stuff. I have used all mine up and don't want to buy a whole quart to do this little job, but you can get a perfect little repair kit from West Marine stores for about $15.
Tony
Removing the bolt
While I have not checked mine yet to confirm, I am pretty confident that the modification Van's has suggested will allow for complete removal of the bolt based on the nature of the modification and the fact that the allen wrench only had to be at a slight angle on mine to engage the head of the bolt.
Jeff
While I have not checked mine yet to confirm, I am pretty confident that the modification Van's has suggested will allow for complete removal of the bolt based on the nature of the modification and the fact that the allen wrench only had to be at a slight angle on mine to engage the head of the bolt.
Jeff
Hey guys - -
I believe if you look at step 11, they show how to make the hole patch, but not how to install it later. They say pull the plastic off, AFTER CURED, and sand the edges of the patch. That leaves you with a hole patch in your hand. You can RTV it into place, or maybe screws. You can remove it then. They did not specify how the patch had to be put back on. You could remove the patch.
This system could allow you to check the torque, and not have to remove the patch, or remove the patch and the bolt if desired. Not a bad idea. The access problem was well addressed, but not the real problem.
John Bender
I believe if you look at step 11, they show how to make the hole patch, but not how to install it later. They say pull the plastic off, AFTER CURED, and sand the edges of the patch. That leaves you with a hole patch in your hand. You can RTV it into place, or maybe screws. You can remove it then. They did not specify how the patch had to be put back on. You could remove the patch.
This system could allow you to check the torque, and not have to remove the patch, or remove the patch and the bolt if desired. Not a bad idea. The access problem was well addressed, but not the real problem.
John Bender
Permanent patch?
The directions are not very clear. I got the impression that the wet fiberglass goes against the shroud and the clear plastic is on top of the patch next to the allen wrench. The patch is permanently adhered to the shroud. That gives you room to check the bolt torque but no room to remove the bolt. If I am interpreting this correctly, then nothing has changed. The bolts will still come loose.
Joe
The directions are not very clear. I got the impression that the wet fiberglass goes against the shroud and the clear plastic is on top of the patch next to the allen wrench. The patch is permanently adhered to the shroud. That gives you room to check the bolt torque but no room to remove the bolt. If I am interpreting this correctly, then nothing has changed. The bolts will still come loose.
Joe
the fix
If the hole in the fiberglass shroud is cut big enough to allow removal of the bolt, then loctite and/or Nordlock washers can be used to prevent loosening of the bolt. Then a permanent patch can be epoxied in place per Van's instructions. Although the bolt can not be removed again, the torque can be checked periodically.
A permanent patch is stronger than a removable cover. Chances are that if the engine ever needs to be removed for repair, the whole shroud will have to come off anyway.
Joe
If the hole in the fiberglass shroud is cut big enough to allow removal of the bolt, then loctite and/or Nordlock washers can be used to prevent loosening of the bolt. Then a permanent patch can be epoxied in place per Van's instructions. Although the bolt can not be removed again, the torque can be checked periodically.
A permanent patch is stronger than a removable cover. Chances are that if the engine ever needs to be removed for repair, the whole shroud will have to come off anyway.
Joe
dick seiders
Well Known Member
Has anyone contacted Rotax yet looking for a permanent fix? They are closed today, but I will be talking with them first thing Monday. If Van is to find
a permanent fix they will first be discussing it with Rotax anyway. I don't see much reason to do the work now and then do it again when the fix is known.
Happy Thanksgiving everyone!
Dick Seiders
a permanent fix they will first be discussing it with Rotax anyway. I don't see much reason to do the work now and then do it again when the fix is known.
Happy Thanksgiving everyone!
Dick Seiders
Jetguy
Well Known Member
See Larry's Post
Dick check Larry Gs post at 748pm yesterday here:
http://www.vansairforce.com/community/showthread.php?t=65020
Dick check Larry Gs post at 748pm yesterday here:
http://www.vansairforce.com/community/showthread.php?t=65020
dick seiders
Well Known Member
WOW! Thanks, John. I never saw the post by Larry because I looked away for about a minute. I am amazed that so many are having the problem! It's clear to me now what a major issue it is. I will take my 12 down and check the bolts this weekend and provide feedback. I only have 43 hrs, but I will look. I will still call on Rotax at Lockwood for input. Does anyone know if the correct size Nordlocks are available and will they fit the recessed hole? Perhaps the Nordlocks with Loctite Blue in combination is the answer?
I won't fail to check this site again for more than a day or two as it's obvious that it is RV12 flyers talking to one another that will save our a--es and likely before any other comunication from mfrs. The only suggestion I want to make to all is when something this hot happens maybe we should put URGENT in caps in the thread title. I rolled right by the thread w/o checking it as I felt -well that's just addressing a 100 hr check issue.
Thanks again John for alerting me.
Dick Seiders
I won't fail to check this site again for more than a day or two as it's obvious that it is RV12 flyers talking to one another that will save our a--es and likely before any other comunication from mfrs. The only suggestion I want to make to all is when something this hot happens maybe we should put URGENT in caps in the thread title. I rolled right by the thread w/o checking it as I felt -well that's just addressing a 100 hr check issue.
Thanks again John for alerting me.
Dick Seiders
Nord-Lock washers
The Nord-Lock NL10 washer dimensions for 10mm bolts are:
10.7mm hole, 16.6mm OD, 2.0mm thick
http://www.nord-lock.com/default.asp?url=337.16.37
I do not know the hole size of the engine mount.
So far I have found two sources:
http://www.mcmaster.com/#nord-lock-washers/=9vo5pp
http://www.clipsandfasteners.com/Nord_Lock_s/210.htm
Joe
The Nord-Lock NL10 washer dimensions for 10mm bolts are:
10.7mm hole, 16.6mm OD, 2.0mm thick
http://www.nord-lock.com/default.asp?url=337.16.37
I do not know the hole size of the engine mount.
So far I have found two sources:
http://www.mcmaster.com/#nord-lock-washers/=9vo5pp
http://www.clipsandfasteners.com/Nord_Lock_s/210.htm
Joe
MartySantic
Well Known Member
I tried to take a measurement at the hangar, but, could not get dial micrometer reading. Way too much stuff in the way. Will have to take a set of calipers out there and measure the ID of the bushing. Anyone have it in their garage?
MartySantic
Well Known Member
Just remember, Nordlock washers and loctite have not been suggested, or approved by Rotax or Van's. They may or may not be a good solution. If you use them, you have become the design engineer, assuming all the responsibilities of the design engineer!!
I am going to modify the shroud, check all four capscrews (at 360 in-lbs), and WAIT for a preventative solution from Van's. And then, most likely reduce the inspection interval until the solution comes our way.
I am going to modify the shroud, check all four capscrews (at 360 in-lbs), and WAIT for a preventative solution from Van's. And then, most likely reduce the inspection interval until the solution comes our way.
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dick seiders
Well Known Member
Marty, you are probably correst, but the Nordlocks, (if the bolts are long enough) and blue loctite can't hurt. The question is how long till we hear from Van's? I don't intend to ground my 12 for an indefiinite period. An interim fix is better than none and the blue loctite sounds like it has been working for those who have tried it. I will plan to re-check the fasteners at each oil change, or 35 hrs.
Dick Seiders
Dick Seiders
Design engineering...
Well, maybe, Marty, and part of the reason for the 2" high sign we see when we climb aboard.
With the present design, every time I head out across the Straight of Juan De Fuca I would be visualizing those bolts jiggling loose like in the video you posted. Not going to go that way.
According to their website Nord-loc washers have been available since 1982, but are apparently not well known in the experimental aircraft world. My DAR ogled the bolts on the brake caliper and asked why they were not safety wired. And again on the prop bolts. I had to explain that they use the Nord-Loc washers, that the bolt heads were not drilled, and that I was not instructed to safety them. I am not sure he had heard of the Nord-Locs.
I have ordered the Nord-Loc washers and if they fit in the holes, will try these, without Loctite. This will allow checking the torque on a frequent basis like you do on the Nord-Loced prop bolts, and with a torque wrench. Nord-loc claims "NORD-LOCK washers positively lock the fastener in a joint which is subjected to extreme vibration or dynamic loads." That would be us. We'll see.
If they loosen then I will probably take off the Nord-Locs and use the split washer and Loctitle 243. Loctite 243 is on the list of chemical stuff that appears in the Rotax manuals although I don't find anywhere where they apply it to the engine mount bolts. But Loctite seems to be the way majority of the industry has gone. I doubt that combining the Nord-Locs and Loctite would be appropriate, but without expert design, who knows?
In rereading the Shroud Modification notice (its not a SB), it looks like Van's feel they have done enough and it is our responsibilty to comply with all Rotax maintenance requirements. I doubt if they are going to propose anything further.
It will be educational to see how the various solutions work out, guys, please keep posting your experiences.
Tony
P.S. Loctite 242 and 243 are both "blue" medium Loctite. I find 242 in the hardware store. I had to order 243 on the internet. 243 is marked "industrial" and has almost twice the break loose torque of 242. They are both in a small inexpensive tube, in a bubble wrap.
Well, maybe, Marty, and part of the reason for the 2" high sign we see when we climb aboard.
With the present design, every time I head out across the Straight of Juan De Fuca I would be visualizing those bolts jiggling loose like in the video you posted. Not going to go that way.
According to their website Nord-loc washers have been available since 1982, but are apparently not well known in the experimental aircraft world. My DAR ogled the bolts on the brake caliper and asked why they were not safety wired. And again on the prop bolts. I had to explain that they use the Nord-Loc washers, that the bolt heads were not drilled, and that I was not instructed to safety them. I am not sure he had heard of the Nord-Locs.
I have ordered the Nord-Loc washers and if they fit in the holes, will try these, without Loctite. This will allow checking the torque on a frequent basis like you do on the Nord-Loced prop bolts, and with a torque wrench. Nord-loc claims "NORD-LOCK washers positively lock the fastener in a joint which is subjected to extreme vibration or dynamic loads." That would be us. We'll see.
If they loosen then I will probably take off the Nord-Locs and use the split washer and Loctitle 243. Loctite 243 is on the list of chemical stuff that appears in the Rotax manuals although I don't find anywhere where they apply it to the engine mount bolts. But Loctite seems to be the way majority of the industry has gone. I doubt that combining the Nord-Locs and Loctite would be appropriate, but without expert design, who knows?
In rereading the Shroud Modification notice (its not a SB), it looks like Van's feel they have done enough and it is our responsibilty to comply with all Rotax maintenance requirements. I doubt if they are going to propose anything further.
It will be educational to see how the various solutions work out, guys, please keep posting your experiences.
Tony
P.S. Loctite 242 and 243 are both "blue" medium Loctite. I find 242 in the hardware store. I had to order 243 on the internet. 243 is marked "industrial" and has almost twice the break loose torque of 242. They are both in a small inexpensive tube, in a bubble wrap.
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MartySantic
Well Known Member
Sure wish we could get some indication from Van's if more is forthcoming? But, as you have stated, Van's has not issued anything as of yet. DR has a good web-crawler and found the file before any "real" or "official" mother ship notification. A simple yes or no would go a long way to remove some of this tension.
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Agree
I agree...Van's is done with the issue...they are not in the business of guarantees. Mine is down for the conditional so I will be very interested in the nordlock results. In fact, I'll probably just go ahead and order them while I've got everything apart. They're not cheap but we don't need that many. And like you said, they do a pretty darn good job of holding my prop on.
I agree...Van's is done with the issue...they are not in the business of guarantees. Mine is down for the conditional so I will be very interested in the nordlock results. In fact, I'll probably just go ahead and order them while I've got everything apart. They're not cheap but we don't need that many. And like you said, they do a pretty darn good job of holding my prop on.
Pete, I don't see how Van's can ignore this, even if all they do is issue a statement that these bolts need to be checked regularly.
Nobody is going to sue a manufacturer for alerting purchasers to the need to check something, but they probably will if the manufacturer has been made aware of a potential problem and takes no action to prevent an accident, even if the action is simply to issue a maintenance recommendation.
In fact they haven't ignored it because they have issued a modifcation to the shroud to make sure owners can access the fourth bolt. They just haven't said why they now think the bolt needs to be accessible, even though everybody here is well aware of the reason.
However, if as others have said, this is not a new problem with Rotax engine mounts and there are acceptable solutions out there, then I would expect Van's to modify their plans to incorporate a suitable fix.
Incidentally, if you use Loctite and then have to remove the bolts some time in the future, can you simply re-Loctite them?
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Oh no, I don't think they have ignored it all. I just think they are done with it. They posted a letter on their website recommending that everyone follow the Rotax guidelines of checking each 100 hours after the first 25 and before the next flight if you have not been. They do not favor adhesives, most likely because they change the torque values required for the same effectiveness. Do I think they may experiment with other washer systems, sure and maybe change their plans to reflect it. The Red one and the Blue one have flown more hours than any RV12 and have not lost a bolt. Personally, mine is complete and now a registered experimental. I like the Nordlock's that are on my brakes and my prop. And I'm probably as curious about my prop staying on as I am about my engine.
You may well be right, but it would be nice to know if they are planning to make any changes to their design. The Nordlocks look good to me, but I have the same concerns as you regarding how Loctite will affect the correct measurement of bolt torque.
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yankee-flyer
Well Known Member
Torque values for Nordlock washers
I'd be a bit worried about uysing standard torque values for the Nordlock washers, too. If I understand how they work, the bolt is strteched (i.e., higher torque applied) until the wedges snap past each other, decreasing the thickness of the washer and reducing the amouny the bolt is stretched. I think that's why the torque values Sensenich specifies for the prop bolts is higher than the standard torque. If you apply the "standard" torque to a bolt with the Nordlocks, once the washers have "locked" the actual torque-- or more correctly, the tensile force on the bolt-- will be less than the recommended value-- I think???
But I'm an aero engineer, not a mechanical with a materials background.
Wayne 120241/143WM
I'd be a bit worried about uysing standard torque values for the Nordlock washers, too. If I understand how they work, the bolt is strteched (i.e., higher torque applied) until the wedges snap past each other, decreasing the thickness of the washer and reducing the amouny the bolt is stretched. I think that's why the torque values Sensenich specifies for the prop bolts is higher than the standard torque. If you apply the "standard" torque to a bolt with the Nordlocks, once the washers have "locked" the actual torque-- or more correctly, the tensile force on the bolt-- will be less than the recommended value-- I think???
But I'm an aero engineer, not a mechanical with a materials background.
Wayne 120241/143WM
Nord-Lock washers form one thicker flat washer
The reason that split-ring lock washers do not work very well is because their spring action tends to push the bolt in the same direction as the load.
Loosening prop bolts with a wrench has convinced me that Nord-Lock washers are much better then split ring washers. As the bolt is slowly turned CCW, it becomes harder to turn the wrench (until the washer halves fall off the incline).
I am not saying that Nord-Lock washers are better than Loctite, but they are much better than split ring-lock washers.
Joe
That is true when the bolts are removed. When the bolt is tightened, the wedges are either already meshed together, or they will easily mesh together without snapping while the bolt is tightened. When using Nord-Lock washers, the bolt can be tightened to any desired torque value as if using flat washers. In fact, a pair of Nord-Lock washers do form one thicker flat washer while the bolt is tightened. And the Nord-Lock washer pair remains meshed together until the bolt is turned ccw (either by a wrench or by the force of joined parts). As the bolt is turned CCW, the two halves of the Nord-Lock washer slide past each other and increase the distance between each other, thus stretching the bolt and making it more difficult to turn ccw. It requires more force to loosen the bolt than it does to tighten it. That is because the bolt has to stretch while the washer halves are separating. Mechanical parts obey the laws of physics. As the bolt turns, it comes to a point where the force of the load pulling on the incline of the bolt threads is equal to the force of the Nord-Lock washer pulling on the incline of its wedges. The bolt then stops turning (unless addition force is added, i.e., with a wrench). A bolt should not be overtightened because it will be stretched even more when loosened.
The reason that split-ring lock washers do not work very well is because their spring action tends to push the bolt in the same direction as the load.
Loosening prop bolts with a wrench has convinced me that Nord-Lock washers are much better then split ring washers. As the bolt is slowly turned CCW, it becomes harder to turn the wrench (until the washer halves fall off the incline).
I am not saying that Nord-Lock washers are better than Loctite, but they are much better than split ring-lock washers.
Joe
Can not recommend
I am no expert at bolt strength or torque values. Therefore I am not recommending anything. But I intend to use Nord-Lock washers and tighten the engine mounting bolts to the torque specified in Van's plans. The bolts will not be stressed any more then when using flat washers. The bolts WILL be stressed more when removed. But hopefully I will never have to do that.
Joe
I am no expert at bolt strength or torque values. Therefore I am not recommending anything. But I intend to use Nord-Lock washers and tighten the engine mounting bolts to the torque specified in Van's plans. The bolts will not be stressed any more then when using flat washers. The bolts WILL be stressed more when removed. But hopefully I will never have to do that.
Joe
Rotax recommended torque
Pete,
No, I did not read that. Thanks for pointing it out. The Rotax and Van's torque values could both be withing the recommended range for those bolts. Sometimes I am tempted to give it a little more for good measure. And sometimes too much can do more harm than good.
Joe
Pete,
No, I did not read that. Thanks for pointing it out. The Rotax and Van's torque values could both be withing the recommended range for those bolts. Sometimes I am tempted to give it a little more for good measure. And sometimes too much can do more harm than good.
Joe
MartySantic
Well Known Member
Pete is correct. The shroud modification .pdf file specially tells us to torque the capscrews per the value in the parts manual (360 in-lbs) vs the value in the plans (310 in-lbs). Scott McDaniels verified this item for me. The plans will be revised to reflect the new value.
WingedFrog
Well Known Member
Flabbergasted
I am flabbergasted by this issue and amazed by the wealth of information that is pouring out of this thread (and thankful to still be several months from torquing my engine mount bolts!). I have just one question:
Assuming that everybody torqued according to VAN's specification, how can you explain that some see screws getting lose and some (i.e. red and blue planes plus a few more I guess) don't?
One explanation I could offer is that some combination prop+engine are subject to more vibrations than others. This would not be unheard of as it is well known that some engines are better balanced just by the play of manufacturing tolerances and this is likely also the case for the props and therefore for the combination.
May be the solution to this issue is in focusing on the source of excessive vibrations rather than on the effectiveness of bolt locking techniques?
I am flabbergasted by this issue and amazed by the wealth of information that is pouring out of this thread (and thankful to still be several months from torquing my engine mount bolts!). I have just one question:
Assuming that everybody torqued according to VAN's specification, how can you explain that some see screws getting lose and some (i.e. red and blue planes plus a few more I guess) don't?
One explanation I could offer is that some combination prop+engine are subject to more vibrations than others. This would not be unheard of as it is well known that some engines are better balanced just by the play of manufacturing tolerances and this is likely also the case for the props and therefore for the combination.
May be the solution to this issue is in focusing on the source of excessive vibrations rather than on the effectiveness of bolt locking techniques?
Interesting, I found the 30 ft-lb torque value on page 28-3 of the Parts Catalog. A torque of 30-ft-lb corresponds within 3 ft-lb to the Nord-Loc guidelines for a zinc plated grade 8.8 M10 bolt, lubricated, using the zinc coated steel Nord-Loc washers.
I am still a bit concerned about the increase in torque required to undo the Nord-Loced bolt, since we don't want to damage the threads in the case, in the event we ever have to remove them.
Also I see in the illustration on page 28-2 of the Engine Suspension Frame that there is a thrust washer on the mounting bolts between the frame and the engine case. I wonder if that could be significant? The bolts are over an inch long, is it possible that without the thrust washer they could be bottoming? That would lead to rapid loosening.
I feel we are junior engineering this and we are over our heads but we are making progress.
Tony
I am still a bit concerned about the increase in torque required to undo the Nord-Loced bolt, since we don't want to damage the threads in the case, in the event we ever have to remove them.
Also I see in the illustration on page 28-2 of the Engine Suspension Frame that there is a thrust washer on the mounting bolts between the frame and the engine case. I wonder if that could be significant? The bolts are over an inch long, is it possible that without the thrust washer they could be bottoming? That would lead to rapid loosening.
I feel we are junior engineering this and we are over our heads but we are making progress.
Tony
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David Paule
Well Known Member
Is there any chance that a drilled-head bolt could be safetied to a hole drilled in the mount?
Geico266
Well Known Member
Let's not over think this. These are 4 cap scew engine mounting bolts with over 12 years of history of being loctited and torqued, and not coming loose again. I like the idea of the Nordlocs, but I am not going to take mine out to add them.
I added loctite and torqued to 26 ft pounds 70 hours ago and they are have not budged since. Torque seal is still there. I torque them to 20 ft lbs to make sure they are tite and all is good. Those bolt are not going anywhere with blue loctite.
I added loctite and torqued to 26 ft pounds 70 hours ago and they are have not budged since. Torque seal is still there. I torque them to 20 ft lbs to make sure they are tite and all is good. Those bolt are not going anywhere with blue loctite.
Torquing bolts
With all the recent discussion about torque values, this link might be of interest.
http://www.boltscience.com/pages/nutorbolttightening.htm
The indicated torque value is not always a good indicator of the amount of bolt tension you actually get. I'm a structural engineer, and when we specify that bolts have to be fully torqued, which means tensioning them (normally 20mm diameter grade 8.8 bolts) into the plastic yield range, we use either load-indicator washers or part-turn torqueing.
Load-indicator washers are fitted with three protrusions that deform a known amount when the bolt is properly tensioned, and this can be measured with a feeler gauge. In the part-turn method, the bolts are pulled up snug tight, marked, and then turned a further specified amount to achieve the required tension. Both of these methods use a direct measure of bolt extension to achieve a known bolt tension, and this eliminates the need to second-guess the effect of friction in the system.
As you can see from the pie chart, even small variations in friction between the contact surfaces can result in fairly large differences in the actual bolt tension for the same measured torque value on the wrench. That's why we don't usually allow the use of torque wrenches for tightening structural bolts, even though torque wrenches are commonly used in the automotive and aircraft industries.
However, the structural bolts we use are not the precision manufactured bolts that are used in these applications, and I would expect that more consistent results would be obtained with a wrench. However, if it hasn't been specified for your application, you need to be careful if applying any kind of lubricant to the threads or other contact surfaces, as it would be easy to exceed the required bolt tension.
Incidentally, the bolts we use can only be used once because they have been tensioned to their limit. If they have to be undone for any reason, they have to be replaced.
With all the recent discussion about torque values, this link might be of interest.
http://www.boltscience.com/pages/nutorbolttightening.htm
The indicated torque value is not always a good indicator of the amount of bolt tension you actually get. I'm a structural engineer, and when we specify that bolts have to be fully torqued, which means tensioning them (normally 20mm diameter grade 8.8 bolts) into the plastic yield range, we use either load-indicator washers or part-turn torqueing.
Load-indicator washers are fitted with three protrusions that deform a known amount when the bolt is properly tensioned, and this can be measured with a feeler gauge. In the part-turn method, the bolts are pulled up snug tight, marked, and then turned a further specified amount to achieve the required tension. Both of these methods use a direct measure of bolt extension to achieve a known bolt tension, and this eliminates the need to second-guess the effect of friction in the system.
As you can see from the pie chart, even small variations in friction between the contact surfaces can result in fairly large differences in the actual bolt tension for the same measured torque value on the wrench. That's why we don't usually allow the use of torque wrenches for tightening structural bolts, even though torque wrenches are commonly used in the automotive and aircraft industries.
However, the structural bolts we use are not the precision manufactured bolts that are used in these applications, and I would expect that more consistent results would be obtained with a wrench. However, if it hasn't been specified for your application, you need to be careful if applying any kind of lubricant to the threads or other contact surfaces, as it would be easy to exceed the required bolt tension.
Incidentally, the bolts we use can only be used once because they have been tensioned to their limit. If they have to be undone for any reason, they have to be replaced.
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ErichKeane
Well Known Member
Thats good to know! We haven't flown yet, so I red-loctited the bottom ones about a week ago, and plan on doing the same on the top ones.
If your blue is holding well enough, I know we don't have to worry
MartySantic
Well Known Member
Bob,
Do any of your structural engineer friends know the mean friction factor (or sometimes called the nut factor) if Loctite 242 or 243 is applied? (The nut factor for the dry case is usually assumed to be 0,2) I can find Loctite information for other grades of Loctite but not for 242 or 243 (the blue's). There is a lot of contradictory information on the web. Some of the websites indicate it is an adhesive, some indicate it is a lubricant, and some indicate it is neutral before it sets up.
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MartySantic
Well Known Member
Thats good to know! We haven't flown yet, so I red-loctited the bottom ones about a week ago, and plan on doing the same on the top ones.
If your blue is holding well enough, I know we don't have to worry
Erich,
SORRY but red may have been a BIG mistake. Please read all of the previous posts regarding the effects Loctite has on the capscrew and the threads in the engine block with respect to the pre-load applied.
Adding Loctite is NOT a simple science. An engineering solution is really required before the general population jumps at a solution.
