XB Rear Engine Mount Warning

[ElliottM]

Hey all,
I am studying mechanical engineering currently and recently we did a Finite Element Analysis on the rear engine mount used in all XB's. (We were able to do this since the company is no longer producing the motorcycles).

Basically, the rear engine mount is prone to failure, sometimes catastrophic. For the normal everyday rider this is no problem, however if you like to do wheelies or happen to get into a front end collision you may want to take this into consideration.

The yield strength for standard aluminum alloys is approximately 40 ksi. In my analysis it was found that doing wheelies at 30 mph has the potential to surpass this yield strength, meaning the mount will begin to permanently deform. This is not good.

For the most part, the mount performs fine. However I would suggest getting it checked out every once in awhile if you enjoy your trick riding. This way you won't end up breaking the mount while riding it and end up taking it down on the road, which has happened.

After I had told a friend of mine about this, he suggested I should post something on here just to let people know. There is no reason for us to stop riding our Buells. I am keeping my 05 Firebolt till the day I die, however I am glad to be at least aware of the rear engine mount.:D

On side note, this was an undergraduate project that I worked on, but I am by no means an expert in the field. My professor, however, is an expert in the field and makes loads of money because he is good at what he does. He has tried many times to get me to stop riding my XB12R, I just refuse.

[konarider94]

wanna post some screen shots of the mesh and the von mises stress. im curious to see what you did. what program did you use? ive used abaqus quite a bit.

im curious how you determined the load on the mount while doing a wheelie. sounds like a pretty cool project.

[ElliottM]

I was trying to figure out how to get pictures up... as soon as I can I will post them. I used ANSYS Workbench.

[konarider94]

click the my pics tab up near the top and upload some, they have to be jpeg. then in the post click add your photo and all of your uploaded pics will come up. just click what you want to post. and what school do you go to?

[Livers]

Great work. I seem to remember threads across the boards maybe last season about failure of these mounts. After a lot of discussion and even more speculation, it came down to 100% of the failures occurred on bikes that had been wrecked.

[squidbuellie]

so basically your saying that our bikes are great looking engineered pieces of artwork. that can only handle casual bike riding? or that

it came down to 100% of the failures occurred on bikes that had been wrecked

[bfletcher]

My professor, however, is an expert in the field and makes loads of money because he is good at what he does.
There is an old saying, "Those who can't do, teach" Careful holding him on the pedestool.

[kyle_dewald]

I do know the rear mount will fail when a car hits you in the right rearset and swingarm, I did a study on it but mine was real world. haha I don't do wheelies and all that but it's good to know what can happen.

[Livers]

Here are the discussions I remembered:

BuellXB (http://www.buellxb.com/Buell-XB-Forum/Buell-Lightning-XB12S-XB12Ss-CityX-XB12Scg/Rear-Engine-mount-broke---crashed)

Buelletinboard (http://www.buelletinboard.com/forums/showthread.php?13034-Rear-Engine-Mount&highlight=motor+mount)

And BadWeb here (http://www.badweatherbikers.com/buell/messages/32777/522852.html?1261140790) and here (http://www.badweatherbikers.com/buell/messages/32777/517072.html?1264638981).

[ElliottM]

Here are a couple screenshots of my analysis using ANSYS Workbench...

http://www.buellxb.com/buell_images/9351_20110319012117_L.jpg
http://www.buellxb.com/buell_images/9351_20110319012211_L.jpg
http://www.buellxb.com/buell_images/9351_20110319012522_L.jpg

@konarider94
I am a senior at Milwaukee School of Engineering in Milwaukee, WI. The loading due to wheelies was based off of assuming the engine mount experienced an acceleration due to the weight of the engine while moving at certain speeds. (i.e. 1.5Gs)

@squidbuellie
I am just saying it is something that riders should be aware of. Anyone with a mechanical engineering background will look at the engine mount and wonder why the engineers allowed for massive stress concentrations on a vital part of the motorcycle.

@bfletcher
Haha I am very familiar with that saying, especially at my school. However this one professor I know for a fact is a very successful engineer and therefore he taught for about 3 years and is now vice president of a company that deals in engine design. (Admittedly, I forget the name of the company...[smirk])

Also, you will notice that only half the part is shown in the screenshots. This is due to the symmetry of the part that was accounted for in the analysis.

[Baal]

This is pretty cool. I appreciate the heads-up.
[up]

[onelogue]

The yield strength for standard aluminum alloys is approximately 40 ksi.
Whats ksi? Is this number a constant? Because i figures the units would be (... /...)

[RudiRulez]

I can already envision a fix, slightly longer bolts and a bridge that joins A to B and could possibly even slot into the recess below C.

That way not all the stress is concentrated on the inside corners next to the bolt holes.

Hmm, wonder if its worth firing up the old CNC mill!

[dave_xb12r]

Why not just make one out of steel?

[RudiRulez]

yeh can do if someone can recreate the casting or has a 3+ axis mill :) , i only have 2 axis on my mill so wouldnt be possible for me. :(

[Livers]

Guys, it's $64 retail, still available. If in doubt, replace it.

http://www.lshd1.com/servlet/Detail?no=776258

[squidbuellie]

right on thanks for the heads up.

[ElliottM]

Yeah there are a couple ways to go about redesigning it, and personally I made a redesign with this project that could be cast (Lost Foam) and require little machining other than bolt holes.

Also, ksi is 1000 psi (lbs/in^2).

You should be able to check it fairly easily, and I would look right around the recesses for the bolts for any signs of cracking or failing. And of course if in doubt it might be better to replace it.

[Stevenc150]

Been here since '08 and a member on 3 Buell forums. Seen LOTS of wrecks caused by cars, other bikes, trick riding, flat out stupidity, etc. - have yet to see or remember seeing a single case where specifically, the rear engine mount suffered a catastrophic failure or otherwise.

Don't get me wrong, I agree it's good to be informed and this post is definitely worth a read. But I'm also a Mechanical Engineer that started as a Machinist. One thing you Cannot predict with exact accuracy, is how metal (especially alloys) will act in the Real World. It's like trying to predict weather or the wave height of a tsunami - there's simply too much information that isn't considered or isn't even yet to be understood.

[americanthunder]

sweet post thank for the heads up [up]

[konarider94]

Don't get me wrong, I agree it's good to be informed and this post is definitely worth a read. But I'm also a Mechanical Engineer that started as a Machinist. One thing you Cannot predict with exact accuracy, is how metal (especially alloys) will act in the Real World. It's like trying to predict weather or the wave height of a tsunami - there's simply too much information that isn't considered or isn't even yet to be understood.

maybe not exact but its pretty damn close. we have a very good understanding of alloys. its not like the composition of alloys change now, we have a pretty good control over materials. even composites are becoming very well engineered. this is why cars and airplanes are getting lighter every year. its fea programs that help us optimize designs. i too am a ME that started as a machinist. I realize im a young engineer but i also understand the newest technology very well.

[Stevenc150]

I understand that, do failure analysis on a fairly regular basis concerning support structures (automotive door pillar beams and suspension). Thing is we do the stress test, get the nice colored renderings showing likely failure points - then I have it machined/formed and do a "real-world" test and it's different. You cannot account for everything because we don't understand everything.

Edit: Again, yet to see/hear of any rear engine mounts suffering catastrophic failures in the "real world". No matter how much analysis is put forth, until something is physically proven - it remains a theoretical outcome.

[BRatigan]

Will hardening the exterior surfaces through type 2 anodization help with distribution of stress loads? Might make the difference.

BR

[ElliottM]

Again, yet to see/hear of any rear engine mounts suffering catastrophic failures in the "real world". No matter how much analysis is put forth, until something is physically proven - it remains a theoretical outcome.

Unsure if you read above posts, but there have been cases where specifically the rear engine mount has failed catastrophically, which I understand as the part breaking completely off of the engine itself, thus causing riders to crash their bike. So far this failure has only be linked to previous accidents, although the possibility of wheelies eventually causing a similar outcome is there.

[kyle_dewald]

Mine broke in a wreck but didn't break causing a wreck.

[boosted]

Will hardening the exterior surfaces through type 2 anodization help with distribution of stress loads? Might make the difference.

BR

Probably not. The stress concentrations will exist regardless of the surface finish. In addition the Anodiziation will, if anything decrease the tensile strength and fatigue resistance due to micro cracks in the coating.

[BRatigan]

I did not know that. This is another good thread.

BR

[hobby10k]

I hit a pot hole on a trip recently, and the bike started to slightly vibrate more than normal. It seemed different but I wondered if it was just in my mind. I quickly checked over the tires and belt etc when I stopped, nothing out of the ordinary.

well I continued on the trip and one my way back it started to vibrate more. so I stopped to really inspect the bike. Thats when I noticed the rear motor mount was broke off. It seemed like it would be ok to at least get back home if I took it easy, so I took it easy and continued on. After I got home thats when I noticed the front motor mount was broke too!! that could have been very very bad!!

so yeah it is prone to failure and that was just from normal riding, I don't wheelie or race, and have never wrecked the bike.

I will post pictures if anyone is interested.

now I need to find a couple motor mount replacements.

[DualSportDad]

I think we would all be interested in pictures. Also year and model of the bike.

[hobby10k]

I dont know how to get a darn picture to show up...I'll try and get the rear up


front:
http://i30.photobucket.com/albums/c332/hobby10k1/PicsArt_1435238593057_zps25ni99s7.jpg

[DougH]

You can upload to photo bucket then get the direct link. Paste thate in the popup when you click image on here.

[dmopar1]

I just want to confirm this rear mount failure, I have an 04 XB12r with 2900 miles on it, never been dropped or in an accident, did probably a dozen wheelies on it, then was on my way to work and hit a pot hole, rear mount snapped the 2 top bolts off on the crankcase and snapped the ears off the mount on the bottom. I'll try to upload some pictures.

[thrstrmech]

never had an issue with mine over the 9-1/2 yrs and 70k plus miles...'03 9s

[TPEHAK]

I just want to confirm this rear mount failure, I have an 04 XB12r with 2900 miles on it, never been dropped or in an accident, did probably a dozen wheelies on it, then was on my way to work and hit a pot hole, rear mount snapped the 2 top bolts off on the crankcase and snapped the ears off the mount on the bottom. I'll try to upload some pictures.
Please upload pictures. I recently hit a pothole so hard even the license plate had been bended by the rear wheel. But the muffler has no marks which is strange. Do you have scratches or dents on the muffler?

[Chicknstripn]

I believe your failure/broken rear isolator is an anomaly.

9+ years on my Buell, and I've put it through some hell, and I've had zero issues. 4 years as a member on the forum and since joining in 2012 this is the first rear isolator failure I've read about.
I've hear of the front isolator having issues but that has also been pretty random.

The study that's referenced in the beginning of this zombie thread doesn't account for all the other systems on the bike that share in the load/stress/strain that the chassis is subjected to in a "typical" riding environment.
The suspension, rear isolator, tie bars(top,rear and front), the V bracket and the front isolator all share the load/stress/strain of everyday riding.

So, to answer your post dmopar, you're that lucky one in one thousand.
It's a crappy feeling. I know. I felt the same way when my crank bearing failed.
It's just the luck of the draw.

Are you the original owner of the bike?
Are you sure the bolts were properly torqued prior to hitting the pot hole? If the isolator bolts were over or under(loose) torqued that would dramatically reduce the service life of the isolator.