A good example are the AN5 prop bolts. Van's on plan page 05-10, tells us to toque 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. .
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?
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
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
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!!
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 or even a letter), 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.
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.
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.
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 bolt is strteched (i.e., higher torque applied) until the wedges snap past each other
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.
With all the recent discussion about torque values, this link might be of interest.
http://www.boltscience.com/pages/nutorbolttightening.htm
snip...
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.
..snip
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