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Engine mounting bolt sheared

Jeff Vaughan

Well Known Member
This is why we do inspections. While doing my condition inspection I found the M10x110 engine mounting bolt was loose when I went to check the torque. Well it wasn’t just loose it had seared off on the case. Not sure how this can happen but it is going to be a Bitch getting the 1-1/4” rest of the bolt out of the case. Total Time 320 hrs
https://vansairforce.net/community/attachment.php?attachmentid=42335&stc=1&d=1684010036
 

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With such a long length maybe there is a resonance problem ? Might try putting some silicone around the mid point of the unthreaded shank, that may damp vibrations and prevent it breaking. Tracy Crook had this issue with the long bolts used to hold the rotary engine layers together.
 
To get bolts like that, I use a gradual, escalating approach.

Start out grinding a screw driver slot in the end with a Dremel wheel. Make the slot big enough and deep enough to get a screw driver that is the full width (10mm)?

Usually it will just screw right out with a screw driver because there is no longer any pre-load tension in the bolt. Try putting a Crescent wrench on the flat blade of the screw driver to get more torque.

If that won't work, next try drilling a medium-sized hole in the end for an Easy-out. It is probably a fairly hard bolt (Socket-head cap screws are usually the equivalent of SAE grade 8 or better), but it will drill ok in the middle, low RPM, high pressure.

If an easy out won't get it, the final step is to drill out the bolt in successively larger steps until you are almost at the thread tap size. From there, sometimes you can grab the end of the thread and pull it out with needle-nose pliers, letting it unwind like a coil spring.

Finally, chase the thread out with a tap. It is really important to get the tap started into the original thread though.

"Every 20-minute job is one broken bolt away from becoming a 2-day ordeal."
 
Thanks Steve for your removal hints. The broken part of the screw is approximately 80 mm in the hole. Ugh
Looks to me that this bolt goes all the way through one side of the case then into threads in the other half. This is in direct line with the hole for the other side engine mount screw which is only 30 mm in length. Just a thought that Rotax saved a manufacturing step by only threading one side of the case needed in the long 110 mm screw on the one side to go all the way into the other half.
Maybe not the best decision on their part if that’s what they did.
 
Thanks Steve for your removal hints. The broken part of the screw is approximately 80 mm in the hole. Ugh
Looks to me that this bolt goes all the way through one side of the case then into threads in the other half. This is in direct line with the hole for the other side engine mount screw which is only 30 mm in length. Just a thought that Rotax saved a manufacturing step by only threading one side of the case needed in the long 110 mm screw on the one side to go all the way into the other half.
Maybe not the best decision on their part if that’s what they did.

If that hole goes all the way through, is there a chance that you could remove the opposing bolt and drill the broken bolt from the other end? That end of the bolt will be smooth and easier to keep the drill centered. Maybe use a transfer punch to start. And the right hand turning drill would help unscrew the broken bolt.
 
Did you do the nose wheel upgrade? I was thinking you could maybe get a collar made like the ones used to match drill the new nose gear. The idea being you have a 1" or 2" metal rod that's the same diameter of the existing hole, with another, smaller (e.g. #40 or #30) hole down the center of the rod. This would ensure that when you try drilling into the remaining portion of the broken bolt, the hole is centered and squared.

It really sucks that you ran into this issue!
 
Just out of curiosity how often do you re-torque those bolts? I remember the initial issue of them coming loose, I put a little loctite in when I installed them. So far so good.

The old dual carb 912 vibration machine strikes again. Need to figure how to turn it into a brass cleaner.
 
Jeff, tough issue - -
You did not ask, but I would select an easy out that could be attached to a 10mm bar to turn it, then make a drill guide sleeve and insert in the hole to drill to an appropriate depth for that tool. Might even see if an extended length of a left turning bit were available to do the job. Then after drilling and cleaning back out the stub. 90% chance that it is not stuck, just fatigued and failed.

I just looked and only found 6" aviation RH bits, but might experiment and silver braze a bit in a long rod for an extension to "make" a left hand bit. Might have to do the same for the screw extractor.

If it is a case bolt, then a good discussion regarding potential case shear and fretting. Even so - -if not leaking and after removing the tip, if the free movement of the crank remains then would leave it. The crank motion should be checked at TDC so piston/ring friction is not included.

May luck be with you!!
 
When a bolt is torqued to correct value then any cyclic tension forces, less than the pre-stretched tension, are not seen by the bolt. Conversely, if a bolt is under less than designed pre-stretched tension then it sees repeated forces that lead to failure. This is why cylinder head bolts and connecting rod cap bolts never fail if torqued correctly.

Another possibility is wrong grade bolt was used. Metric cap screws come in different grades. Grade 8 has less tensile strength then grade 12.
 
Rotax MMH from September 2022 states that the M10x110 bolt must be of strength category 10.9 and goes on to specify that the bolt is torqued to 44 ft. lbs. using LOCTITE 243. See 71-00-00 page 20
 
Rotax MMH from September 2022 states that the M10x110 bolt must be of strength category 10.9 and goes on to specify that the bolt is torqued to 44 ft. lbs. using LOCTITE 243. See 71-00-00 page 20

Hmm. That’s interesting…. The same size, and 10.9 grade, bolts are used on the 12iS mount, yet the MMH 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?

Edit: Received this response from the Rotax dealer that monitors the Rotax Owners forum:

“It seems that the 912iS manual may be incorrect and not updated regarding the bolt torque specification and the inclusion of Loctite. The Rotax 915iS manual reflects what the 912 and 914 manuals state for the bolt torque (60 NM) and the use of Loctite.

We have also encountered a similar issue with the valve cover bolt torque specification for the 912iS.”
 
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I'm confused also. I've looked at the latest MMH for 912iS that I could find and the torque value is 29.5 (sometimes in NM) with no mention of LOCTITE. The iS MMHs are older than the September 2022 912ULS one I cited. This is what the MMH I cited said at the bottom of each page: "Effectivity: 912/914 Series" Maybe in Rotax speak that means all 912/914. Maybe Scott from Vans can help us out here.
 
If we can’t get an authoritative answer here, I can post the question on the Rotax Owners forum.

Edit: Received this response from the Rotax dealer that monitors the Rotax Owners forum:

“It seems that the 912iS manual may be incorrect and not updated regarding the bolt torque specification and the inclusion of Loctite. The Rotax 915iS manual reflects what the 912 and 914 manuals state for the bolt torque (60 NM) and the use of Loctite.

We have also encountered a similar issue with the valve cover bolt torque specification for the 912iS.”
 
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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.
 
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.

Edit: Received this response from the Rotax dealer that monitors the Rotax Owners forum:

“It seems that the 912iS manual may be incorrect and not updated regarding the bolt torque specification and the inclusion of Loctite. The Rotax 915iS manual reflects what the 912 and 914 manuals state for the bolt torque (60 NM) and the use of Loctite.

We have also encountered a similar issue with the valve cover bolt torque specification for the 912iS.”
 
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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.
 

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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.
 

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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.
 
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.
 
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.
 
I do follow directions so I am positive I installed per Vans/Rotax instructions and used 243 loctite. Confirming the bolts are 10.9
 
Scott, thanks for the info regarding the KAI telling us where to find the torque values on these bolts. It's been about 12 years since my partner and I hung the engine and I can't find the original Vans KAI, however the KAI from 2014 says: "Torque the mount screws to the value found in the ENGINE SUSPENSION FRAME ASSY. Section 28 of the Rotax Illustrated Parts Catalog." The IPC shows the value to be 30 ft. lb. I didn't look at every version of the KAI or IPC, but I believe the value to be 30 without any reference to LOCTITE. I still can't find an explanation for why the torque value in the MMH is different from the IPC.
 
Torque check v locktite

I don't believe a Loctited bolt is the same as a Dry bolt for the purposes of a torque check. Once the Locktite is broken it will impose a stiff running torque on the bolt but it may not be the same as a dry bolt.
I was a main player in the original loose bolt issue when the issue first arose. My original KAI drawings for the motor mount installation actually specified a torque value for the bolts - 26 ft-lb. Vans probably regrets ever having done that. Now they refer to the Rotax installation manual. As Scott points out, the torque value should have been 30 ft-lb. But, in addition, the later KAI drawings were revised to show that the powder coating is to be scrapped off of the engine mount at the mating surfaces to the engine. The original drawings did not so state. I believe that the low bolt torque of 26 ft-lb contributed to fretting wear of the powder coating on these original installations, like mine, and resulted in loosening of the bolts.
Back then, there was a lot of back and forth discussion of using Loctite. My thinking was that it would not be possible to check torque on the bolts if they were locked in with Loctite. The function is in the name!
Also, if there is fretting wear at the mating surfaces, then a Loctited bolt could be loose and torque seal and even a torque wrench may not reveal that.
Am I over thinking this!?
Anyway, I see the Rotax installation manual now states Loctite 243. Without doing a lot of fruitless research I don't know if the Rotax instructions included that requirement back 13 years ago, but I doubt it I also don't know how you check a Loctited bolt without breaking the seal, does Rotax speak to that somewhere?
 
In 2013 I did my first annual. I had torqued the engine bolts to 18 ft-lbs during my build and found them loose. At that time ROTAX changed the torque to 30 ft-lbs. I torqued them to the new value, and they haven’t budged since when I check them at annual.
 
I don't believe a Loctited bolt is the same as a Dry bolt for the purposes of a torque check. Once the Locktite is broken it will impose a stiff running torque on the bolt but it may not be the same as a dry bolt.
I was a main player in the original loose bolt issue when the issue first arose. My original KAI drawings for the motor mount installation actually specified a torque value for the bolts - 26 ft-lb. Vans probably regrets ever having done that. Now they refer to the Rotax installation manual. As Scott points out, the torque value should have been 30 ft-lb. But, in addition, the later KAI drawings were revised to show that the powder coating is to be scrapped off of the engine mount at the mating surfaces to the engine. The original drawings did not so state. I believe that the low bolt torque of 26 ft-lb contributed to fretting wear of the powder coating on these original installations, like mine, and resulted in loosening of the bolts.
Back then, there was a lot of back and forth discussion of using Loctite. My thinking was that it would not be possible to check torque on the bolts if they were locked in with Loctite. The function is in the name!
Also, if there is fretting wear at the mating surfaces, then a Loctited bolt could be loose and torque seal and even a torque wrench may not reveal that.
Am I over thinking this!?
Anyway, I see the Rotax installation manual now states Loctite 243. Without doing a lot of fruitless research I don't know if the Rotax instructions included that requirement back 13 years ago, but I doubt it I also don't know how you check a Loctited bolt without breaking the seal, does Rotax speak to that somewhere?

Thanks Tony. I agree and have always thought the purpose of loctiting a bolt was prevent vibration and other forces from loosening it. I see re-torquing as breaking the loctite seal that you set up to help prevent those forces from causing the problem in the first place.

I'll let you engineers debate the finer points. I'm just a dumb pilot....if I pull back on this thing it goes up right?
 
Thanks Tony. I agree and have always thought the purpose of loctiting a bolt was prevent vibration and other forces from loosening it. I see re-torquing as breaking the loctite seal that you set up to help prevent those forces from causing the problem in the first place.

I'll let you engineers debate the finer points. I'm just a dumb pilot....if I pull back on this thing it goes up right?

For instance... You don't remove cylinders from engine to check connecting rod cap bolts. The bolts are assembled at required torque specification and then cotter-keyed and remain so until engine overhaul.
 
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?
I'm right at the point of mounting the 912iS Sport engine. The KAI directed me to the MMH 70-00-00 but when going there I had to specify the engine model and serial number. Is it possible that the MMH is different for the 912ULS vs the 912iS. I don't have a ULS serial number to check if there is a difference. As of today it specs "Tightening torque of M10x110 and M10x35 hex screws is 40 Nm (353.92 in lb.)"
At the bottom of the page is this: effectivity: 912 i Series; Edition 1/Rev. 0; page 24; July 01/2012. (!) The date is troubling because they didn't have the injected engine then.
 
I'm right at the point of mounting the 912iS Sport engine. The KAI directed me to the MMH 70-00-00 but when going there I had to specify the engine model and serial number. Is it possible that the MMH is different for the 912ULS vs the 912iS. I don't have a ULS serial number to check if there is a difference. As of today it specs "Tightening torque of M10x110 and M10x35 hex screws is 40 Nm (353.92 in lb.)"
At the bottom of the page is this: effectivity: 912 i Series; Edition 1/Rev. 0; page 24; July 01/2012. (!) The date is troubling because they didn't have the injected engine then.
No mention of LocTite that I can see either.
 
I don’t know how many of the ~800 flying 12’s Scott referenced are iS, but I have to assume all of us used the 40 Nm value referenced in the MMH, since that’s where the KAIs tell the builders to find the mounting torque value. It’s also the value I use during my CIs to verify tightness. I can’t speak to the 2012 publication date, but it’s been revised since then, 2018 most recently, and that section obviously wasn’t changed. So, right or wrong, I’ll continue to check them at 40 Nm. And I’ve not found any loose since my last CI at 200 hrs. I’ll be starting my 300 hr Rotax inspection and CI next week, so will hopefully not have to eat my words.

Edit: Received this response from the Rotax dealer that monitors the Rotax Owners forum:

“It seems that the 912iS manual may be incorrect and not updated regarding the bolt torque specification and the inclusion of Loctite. The Rotax 915iS manual reflects what the 912 and 914 manuals state for the bolt torque (60 NM) and the use of Loctite.

We have also encountered a similar issue with the valve cover bolt torque specification for the 912iS.”
 
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Just to update on my question about the proper torque value on the engine attach bolts, I sent a request to Rotax with that question. Here's the response.

"Hello! I'm Alex with Motive Aero, the Rotax ISC for the Western United States.

I received your question regarding torque values on your Rotax 912 ULS from my friends over at Rotax proper. I have confirmed that in this instance the 44 ft-lb value with loctite is correct, and I would always defer to the maintenance manual if there's a question or apparent conflict.
Feel free to contact me with other questions or I can be of further assistance, I should be able to at least track down someone who can help.

The latest documentation for all Rotax engines can be always be found at https://www.flyrotax.com/p/service/technical-documentation, for Rotax parts, support, and training our website is Motive.Aero"
 
Happiest RV 12 owner this week

Sorry for the 90 degree photo. Never had this issue B4.
So Today I tackled the dreaded sheared bolt.. I waited till I had all the right tools.
I made a drill guide and purchased a drill bit extension for a 7/64 left handed drill bit. I also ordered a tap extension that would fit into the 10mm hole. I squirted Kroil penetrating lubricant with silicone into the hole 24 hours B 4. I new that the bolt had moved out of the hole by about 1-1/8” before it sheared so I was hoping it would easily come out. It actually moved out slightly when I was drilling it. Maybe a 1/4”. With Ez out in place it backed right out! Phewwwww
Happy dance done along with shots of my Manatawny Still Works Whiskey.
Tomorrow I will clean out the hole real well. From the looks of the thread it looks like I am the cause. Some threads had wider spacing which is typical of an over torque. Interesting that it backed out. Maybe it broke in place and then backed out. Ok now to put it back with Blue Loctite and 44 lbs of torque.



https://vansairforce.net/community/attachment.php?attachmentid=42844&stc=1&d=1684965741
 

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Great idea to use a left hand bit. I wouldn’t have thought of that. I’ll remember that if I ever have a similar issue.
 
Jeff, Excellent result. Happy to see that stud in the light.

Your grin says it all . . . .
 
Nm vs. Ft-lb.

Maybe it broke in place and then backed out. Ok now to put it back with Blue Loctite and 44 lbs of torque.


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Please be careful. The spec of 44 Newton meters is not the same as Ft-lb. The spec in Ft-lb is 30 Ft-lb.! 44 Ft-lb of torque would badly over torque the bolt.
 
To close the loop in this thread regarding the discrepancy between the ULS 60 Nm and iS 40 Nm mounting-bolt torque values, I received this response on the Rotax Owners forum from the Rotax dealer that monitors that site. And I went back to my associated posts on this subject to add this information for those researching it in the future:

“It seems that the 912iS manual may be incorrect and not updated regarding the bolt torque specification and the inclusion of Loctite. The Rotax 915iS manual reflects what the 912 and 914 manuals state for the bolt torque (60 NM) and the use of Loctite.

We have also encountered a similar issue with the valve cover bolt torque specification for the 912iS.”
 
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As one of the earlier builders my bolts were torqued to 30 ftlb as per the recommendations at the time. I also used Loctite 243 for added security. So the question is, do I re-torque them to 44 ftlb?
I would have to undo the bolts and try to remove all the Loctite from both the bolts and engine case threads, which probably wouldn't be easy.
Alternatively, do I leave things as they are in the absence of any apparent problems during the last 8 years and the fact that I used the correct torque at the time.
If Rotax issued an SD requiring the higher torque, I would comply, but how critical is it? There must be a lot of 12's flying with the lower torqued bolts, probably including Vans own demonstrators.
 
At the very least… use torque seal inspection lacquer to mark the bolt head for future inspection to verify bolt has not loosened in use….
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As one of the earlier builders my bolts were torqued to 30 ftlb as per the recommendations at the time. I also used Loctite 243 for added security. So the question is, do I re-torque them to 44 ftlb?
I would have to undo the bolts and try to remove all the Loctite from both the bolts and engine case threads, which probably wouldn't be easy.
Alternatively, do I leave things as they are in the absence of any apparent problems during the last 8 years and the fact that I used the correct torque at the time.
If Rotax issued an SD requiring the higher torque, I would comply, but how critical is it? There must be a lot of 12's flying with the lower torqued bolts, probably including Vans own demonstrators.

I'm in the same boat, Rob. The builder made a note that he had torqued them to 30 ft lbs using blue Loctite. My machine has been flying for a similar time to yours and has just ticked over 700 hours - torque seal still in place. I plan to leave well enough alone. If they were going to loosen, it would have happened a long time ago. Bolts usually get harder to move over time, not the other way round.

Jack
 
At the very least… use torque seal inspection lacquer to mark the bolt head for future inspection to verify bolt has not loosened in use….
-

In the context of what started this thread, that seems like a great way to skip over a broken bolt and assume everything is good because the colors are lined up.

If you are checking that a bolt that has been in service and you can't see anything about the faster on the other side, the only way to know is to put a tool on it.
 
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