Engine mounting bolt sheared

[rvbuilder2002]

Originally Posted by Bob Y

Hmm. That’s interesting…. The same size, and 10.9 grade, bolts are used on the 12iS mount, yet the HMMH for the iS (71-00-00, p 24) says to tighten to only 29.5 ft-lbs (40 Nm vs. 60 Nm). Big difference. Wondering why?

I wonder what the Rotax install manual states?
I believe that is what was used to specify the value in the KAI.
Something that has been an issue many times over the years related to things specified by Rotax is they started out with one spec, and then later on changed it. In some cases multiple times over quite a few years.
I the only way anyone at vans ends up finding out is when people ask why vans didn’t do what Rotax said to do.

As for the broken bolt, that was the cause for this thread, everyone should keep in mind the big picture when looking for an explanation for issues like this…
There is somewhere around 800 RV 12s flying now and as far as I am aware there has not been many reports of issues with engine mount to engine case attachment bolts with the installation process currently specified in the KAI.
This does seem to amplify the importance of following the inspection procedures, specified by Rotax, which includes checking the torque of the engine mount to engine case attached bolts, every 100 hours.

[Bob Y]

Yes, Scott, one would expect to find this data in the installation manual, but I sure couldn’t find it there. Even the KAIs point us to the MMH for this information. I’ve posted this question on the Rotax Owners forum and will report what I hear there.

[cactusman]

Originally Posted by rvbuilder2002

I wonder what the Rotax install manual states?


This does seem to amplify the importance of following the inspection procedures, specified by Rotax, which includes checking the torque of the engine mount to engine case attached bolts, every 100 hours.

I'm not sure it calls for the actual re-torque of the engine case bolts each year/100.

It details an "inspection" of the engine suspension and bolts. I don't re-torque them - I do inspect them for movement/black rings/signs of backing out/gaps. Original torque seal still there. My approach is to inspect and then re-torque if any signs of loosening.

Happy to be corrected if I am wrong.

[Bob Y]

I interpret this schedule to indicate a torque check every 100 hrs. I’m not sure how else to check for proper “secure fit”. And the Van’s maintenance check list is clearer.

[Jeff Vaughan]

https://vansairforce.net/community/a...1&d=1684333973

[cactusman]

Originally Posted by Bob Y

I interpret this schedule to indicate a torque check every 100 hrs. I’m not sure how else to check for proper “secure fit”. And the Van’s maintenance check list is clearer.

Earlier on (someone with better search abilities than I perhaps can find it..2012...2013...?), there was an extensive thread on these bolts backing out and being discovered on initial annual. Loctite was added to the KAI and I don't recall much reporting on this until now. Just saying that the annual re-torquing of these M10 bolts might have contributed to this failure, and I question whether that is completely necessary from an inspection standpoint. All actions have equal and opposite reactions... "You guys aren't rotating fast enough... 3 degrees per second..." certain VP of flight ops - 2 tail strikes later....nevermind.

[rvbuilder2002]

Originally Posted by cactusman

Earlier on (someone with better search abilities than I perhaps can find it..2012...2013...?), there was an extensive thread on these bolts backing out and being discovered on initial annual. Loctite was added to the KAI and I don't recall much reporting on this until now. Just saying that the annual re-torquing of these M10 bolts might have contributed to this failure, and I question whether that is completely necessary from an inspection standpoint. All actions have equal and opposite reactions... "You guys aren't rotating fast enough... 3 degrees per second..." certain VP of flight ops - 2 tail strikes later....nevermind.

It is a stickied thread at the top of the RV 12 forum. The issue at the time was that the KAI had a typo and the wrong torque value was specified. Once that was corrected and builders began using the correct torque value reports of bolts loosening up Dropped to zero.

[rvbuilder2002]

Originally Posted by cactusman

I'm not sure it calls for the actual re-torque of the engine case bolts each year/100.

It details an "inspection" of the engine suspension and bolts. I don't re-torque them - I do inspect them for movement/black rings/signs of backing out/gaps. Original torque seal still there. My approach is to inspect and then re-torque if any signs of loosening.

Happy to be corrected if I am wrong.

I don’t think that page would contain an Attention note stating “be sure to use the specified tightening torque” if the intent of the inspection process wasn’t to confirm the torque of the fasteners by using a torque wrench.

[Jeff Vaughan]

I do follow directions so I am positive I installed per Vans/Rotax instructions and used 243 loctite. Confirming the bolts are 10.9

[Bob Y]

I know you can find a lot of conflicting information on the web, but these values are close to our discussion values. It appears the wet (ULS Loctite application) vs. dry (iS guidelines) may be the answer. It does make sense regarding differing torque values. So once the Loctite is dry, I guess use the 60 Nm value? Now I wonder why Loctite for ULS but not the iS?