center stand bolts sheared

[mig]

well an interesting thing happened to me yesterday. I was putting the bike on the centerstand and as it was going over center it leaned to the left on me. Just about fell over but the side stand saved the drop, but for the life of me I couldn't get the bike up and level. As i looked down I could see what appeared to be a bent center stand? I man handled the bike level and moved foward to get it off the center stand. Upon inspection it appeared that the left bolt had sheared inside the bushing nut. i played with the center stand and put it in the up position and decided to go to the dealer. I was fortunatley 3 blocks away. But as I crossed the first intersection I heard this noise and my bike jumped up. As i looked in my mirror I could see the whole center stand in the road. i made my way over to the curb and ran out to get the unit.

so it appears that both bolts had sheared and the spring was actually holding the thing up.

ordered the parts, 36 dollars and will come next week, so my question---- how often has this happened. i park my bike on center stand about 99% of the time. Freak venture or semi common occurence. its a 2007

thanks

Miguel

[dirtrider]

Afternoon Miguel

 

You are the second person with a 1200 hexhead that I have heard of that happening to. The other occurrence "we thought" was because the bike was trailered about 800 miles with the bike on the center stand (guy didn't know any better).

 

Interesting: now we all have something else to keep an eye on as our 1200's get older.

 

[mcollect]

The bolts need to be greased every so often, I noticed my center stand made funny noises so I removed the bolt and it was dry. I greased the bolts problem solved. One more thing to add to yearly maintenance.

[bobbybob]

I wonder if greasing is the answer? No mention of the condition of the old bolts, i.e. had metal been worn away to where they were noticeably smaller diameter, affecting their strength? Or were they normal in appearance but just sheared due to fatigue? If fatigue, BMW needs to address this issue. Could be a safety issue, whether riding or putting the bike on stand. The first bolt sheared when he placed the bike on the stand, and the other immediately after when it endured the full load of the bike by itself.

[mig]

i am wondering about the grease. The bolts ride in a bushing that is able to rotate. Not sure also because the bolts came locktighted into the bushing

[mig]

here is my attempt to post a picture

[OoPEZoO]

 

Non clicky version for you

[racer7]

There are a few reasons these bolts can shear but the basic one is that it a 10 mm and ought to be a 12 mm for the stresses it sees. Also the threads are shear loaded, a recipe for breaking bolts as anyone who passed fasteners 101 knows. To top it off, if you are in the habit of turning the bars while the bike is on the centerstand you are imposing tremendous twisting forces on this improperly designed bolt system (listen for the sidetand popping around on the pavement and you'll understand this point).

 

You were very foolish to ride the bike with a broken stand and lucky it didn't end up in the rear wheel and pitch you off, a problem that has been noted by others...

 

I understand the limits of the design and don't twist my bars while using the centerstand. I also carry spare bolts just in case- a couple 10MM X 30MM from the local autoparts store for about a dollar rather than the factory ones which IIRC were a bit pricey just to have rattling areound as spares.

[Frustrated_Diver]

So far in 54,000 miles i’ve had two center stand bolts sheer off. Now that i have several replacement bolts in stock, i don’t expect to ever have the problem again. 

 

Each night as i gently put the bike up on the center stand (well as gently as one can heave that much weight around), i wonder how such a wimp as me could break such a hefty looking bolt. Thanks for the explanation of the poor design. Putting the spring back on is the hard part.

 

[lkchris]

Currently being discussed on Pelican R1100S forum where consensus is breaking is result of bolt being loose. Check tightness often. Latest bolts arrive from BMW with encapsulated thread lock applied. "Poor design" conclusions are amusing at best. When the screw is properly tightened, the stress is on the taper, not the threads.

[Alfred02]

"Poor design" conclusions are amusing at best. When the screw is properly tightened, the stress is on the taper, not the threads.

+1

These failures are rare at best.

If we go by that, then every single part of every motor vehicle ever build is a "poor design", as you will find that "all" of them have broken at some stage.

 

[racer7]

Bolts are intended to be compression fasteners and carry loads in tension. In the case of the RT stand the load can indeed land as shear on a threaded part of the bolt. Twisting the centerstand is what makes it a lot worse.

 

If you want a lesson on how to design a bolt system the easiest place to start are Carroll Smith's ubiquitous texts on race car design. I believe the "Design to Win" volume has the most info on various fastener systems though it is a bit dated on proprietary systems. Race cars and motorcycles share the need to deal with two common issues- the need for lightness and the need to withstnad extrmes of vibration and shock compared to say, a softly suspended street car...

 

Yes many existing aystems use bolts simultaneously in both tension and shear and good ones make sure any shear load cannot land on a threaded part of the bolt. Reason is simple - threads create stress risers. Doesn't take nearly as much abuse to shear a bolt at a thread. If it loosens a little it will certainly get even easier.

 

The bolts provided by the factory are low grade IIRC (metric 8 which is not the same as our grade 8 but more like our grade 5). And some degree of flex is neeeded for the system to work at all. The current design doesn't allow for easy inspection either.

 

The fact the a reasonable number of these have failed in ordinary use is sufficent to call it a not very good design. Obviously 10 mm bolts are not being broken by the almost non-existent tension load they see in the factory design. I suspect 12 mm bolts would be strong enough to prevent tihs but the design is still a wrong use of that fastener. Anyone ever have any centerstand ever fail on any other bike you've owned where it wasn't damaged by a hit of some sort?

 

To keep the stock system intact use it only on suitable surfaces and avoid twisting the bars once the load is on the stand. Essentially you're trying to distort a triangle doing that- the leverage on those 10 mm bolts is huge. Resisting side movements while the bike is trailered on the centerstand would do the same thing as twisting the bars re putting stress on those bolts.

 

 

[EddyQ]

if you are in the habit of turning the bars while the bike is on the centerstand you are imposing tremendous twisting forces on this improperly designed bolt system (listen for the sidetand popping around on the pavement and you'll understand this point).

 

Yup, I'm one of those. But not anymore. . .

 

So, where did you get a better than OEM bolt? I'm tempted to pull mine out just to check it and replace with a stronger grade bolt.

[Joe Frickin' Friday]

In the case of the RT stand the load can indeed land as shear on a threaded part of the bolt.

Only if the bolts are loose (see below).

 

Twisting the centerstand is what makes it a lot worse.

Worse, but not "a lot" worse (no really, see below).

 

And some degree of flex is neeeded for the system to work at all.

Nope. Nothing needs to flex in order for the stand to rotate on its pivot pins.

 

The fact the a reasonable number of these have failed in ordinary use is sufficent to call it a not very good design.

Do we have reports numbering anything close to (for example) the number of oilhead final drive failures, or hexhead fuel boss cracks? The OP is one, and Dirtrider has pointed to another. So far that makes...two (that I'm aware of).

 

Obviously 10 mm bolts are not being broken by the almost non-existent tension load they see in the factory design.

There's plenty of tension (seriously, see below).

 

Oh good, you've made it below! It's time for an engineering analysis of what's going on in those bolted joints.

 

R1200RT with full tank of gas weighs about 600 pounds. When up on the centerstand, the front wheel is still carrying about 50 pounds of weight, so the centerstand is bearing 550 pounds of motorcycle deadweight.

 

If the rider climbs aboard, he's sitting pretty much directly above the stand, so let's add 225 pounds: now we have 50 pounds on the front wheel, and 775 pounds on the stand. That makes 388 pounds of shear force on each of the centerstand's two bolted joints.

 

Can those bolted joints resist that shear force solely through the static friction between the stand and the pivot pins, without incurring any bending loads in the bolts?

 

Each bolt is a microencapsulated M10, tightened (hopefully) to 42 N*m. The formula for calculating bolt tension as a function of tightening torque is:

 

F = T/(K*D)

 

where:

T = bolt torque

D = bolt diameter

K = friction factor

 

The friction factor for a clean, unlubed bolt coated with threadlock compound, according to these guys, is 0.2. So:

 

F = 42/(0.2*0.01)

 

F = 21000 N, or about 4720 pounds of tension on each bolt.

 

OK, so that's how tight each bolt is squeezing. We still have to figure out how much shear force the joint can take without slipping. According to these guys, the coefficient of friction for steel on steel can vary anywhere from 0.16 to 0.8, depending on whether the joint is lubricated or not. Assume the worst: that somebody disassembled your stand and dipped it in oil, then reassembled it, so the coefficient of friction is a paltry 0.16. This means that under the worst circumstances, each bolted joint can resist 0.16 * 4720 = 755 pounds of shear load before it shifts and starts applying side load to the bolt. We established up above that each joint sees about 388 pounds of shear load when the rider is sitting on the bike, so we've got a safety factor of about two. Not bad.

 

What about if the rider is twirling the handlebars? Well, there's 50 pounds of downforce on the front tire when it's on the stand. The front tire's contact patch is 33 inches from the centerstand. Assume the tire's coefficient of friction is 1, so it can exert as much as 50 pounds of sideways force. So it can apply 50*33 = 1650 inch-pounds of twisting moment to the centerstand. The two bolted joints are ten inches apart, so each bolted joint would see 1650/10/2 = 83 pounds of shear load from handlebar-twirling. Since that load is directed horizontally, and the deadweight load is directed vertically, we add them as vector quantities to get SQRT(83^2 + 388^2) = 397 pounds of shear load on each bolted joint, which is still giving us a safety factor of about two.

 

Bottom line? As noted above, if the bolts are properly torqued, then all of the foreseeable shear load is taken up by the bolted joints, and none of it by the bolts themselves. Even if the rider is actually sitting on the bike and casually twisting the handlebars back and forth.

 

Note, however, that if the pivot pin lube dries out, it's possible that one pivot pin could exert a loosening torque on its bolt when the bike is being put up on the stand, and the other pin could loosen its bolt when the bike is coming down off of the stand. Once the bolts begin to loosen, the above analysis no longer holds - the bolts will bear bending loads and are likely to snap at some point. This points to the importance of maintenance: the centerstand should be removed and lubricated periodically to insure that those pivot pins don't dry out and bind in their sockets.

 

 

[hopz]

 

F = T/(K*D)

 

where:

T = bolt torque

D = bolt diameter

K = friction factor

 

The friction factor for a clean, unlubed bolt coated with threadlock compound, according to these guys, is 0.2. So:

 

F = 42/(0.2*0.01)

 

F = 21000 N, or about 4720 pounds of tension on each bolt.

 

 

So it can apply 50*33 = 1650 inch-pounds of twisting moment to the centerstand. The two bolted joints are ten inches apart, so each bolted joint would see 1650/10/2 = 83 pounds of shear load from handlebar-twirling. Since that load is directed horizontally, and the deadweight load is directed vertically, we add them as vector quantities to get SQRT(83^2 + 388^2) = 397 pounds of shear load on each bolted joint, which is still giving us a safety factor of about two.

 

 

 

I love it you talk like that....

 

 

[dirtrider]

 

 

As Mitch mentioned those 10mm flat head bolts should have plenty of strength if properly torqued & remain tight through out use. Even a plain 10mm 8.8 bolt should have well over 6000 lbs shear capability each not to mention the joint friction of the bushing tightly clamped to the stand.

 

Problems can arise in both PROPER torque & bolt quality. Seeing as those bolts are flat head (tapered seating) & also micro encapsulated, applying a proper torque value when installing is difficult at best as the micro encapsulation can cause torquing issues as well as the angles of the tapered head bolts vs matching angles in the stand can cause torque measurement issues due to high bolt head friction. Basically flat head bolts are difficult to torque properly during initial assembly but even more difficult to torque correctly at re-assembly during service. Then add in the micro encapsulation to make it even more difficult to achieve proper assembly torque while assembling or servicing.

 

In looking at the center stand to frame attachment it is obvious the major loading or force that joint sees is during the placement of the bike (on) the center stand. The pivot stop for the stand is only about 25mm from the bolt/bushing center with the lower leg having an extension length from the stop of about 250mm.

That is one heck of a leverage ratio & can significantly load that bushing & bolt as the heavy mass of the bike hits that stand stop at velocity through that tremendous leverage ratio.

 

I would think the forces involved when moving the bike around on the center stand would be very low compared to the moving bike mass hitting the center stand stops when placing the bike on the center stand. Even if sitting on the bike while moving the bars around the imparted forces would be very low compared to the initial placement of the bike on the center stand. To make it even worse if the added weight of full top box & full side panniers as well as a full camping gear load on the back seat is figured in the bike + gear moving mass hitting the center stand stops through that lever ratio must be tremendous.

 

Obviously there are very few failures even on high mile 1200RT bikes so BMW must have done their calculations somewhat right or we would have seen many more failures by now.

 

On the very few failures we have seen (or heard about) who knows if it was due to a simple defective bolt, or an improper re-assembly from service work, or inadequate (or excessive) original assembly torque, or corrosion in/on the bolt or bushing interface causing excessive bolt tension, or ????.

 

[EddyQ]

centerstand should be removed and lubricated periodically to insure that those pivot pins don't dry out and bind in their sockets.

 

Nice analysis Mitch. However, I not only twist the handlebars while sitting on the centerstand, I never took it apart.

So it will come apart soon. But if I do have it apart and there is a stronger grade bolt, I sure would like to install it. Save the old one as a spare. So anyone know where I could get such a bolt?

[dirtrider]

Evening Eddy

 

We don't know what the BMW OEM bolt strength is so to go stronger is a guess.

 

I would imagine the OEM is either an 8.8 or a 10.9. (but this is just an educated guess)

 

That would mean that getting a flat head 10mm X 30mm 1.5 thread pitch with a 12.9 rating should be stronger than OEM.

 

If those bolts are kept tight the grade shouldn't be a big deal as the bushing to stand friction should take the loading not the bolt shear strength. If you are relying on the bolt shear strength then the bolt isn't torqued properly.

 

If using non OEM BMW bolts be sure they are corrosion resistant & use some Loc-tite on the threads (the OEM have micro encapsulation as a factory Loc-Tite. Seeing as the bushings have blind holes put a dab of Loc-tite on the internal threads as well as the bolt's external threads (blind holes tend to push the Loc-Tite back out along the threads as the bolt threads in due to pressure build)

 

[EddyQ]

Thank DR. Yeh, a lot of socket head higher grade bolts are black oxide and likely rust up quickly. However, I did quickly find a zinc grade 12.9.

 

Link

[dirtrider]

Afternoon Eddy

 

That link shows a cap screw I believe you are looking for a flat head (flat head tapered seating).

 

 

[EddyQ]

Gee, I finally found a place that sells a 12.9 rated flat head 10mm X 30mm.

 

Bolt Depot

[Joe Frickin' Friday]

I'm glad this thread came to the surface again. My bike was only three years old the last time I saw this thread; now it's seven years old, and I still haven't disassembled my centerstand to re-grease the pivots. Now I know what's next on my to-do list...

[Bernie]

I am also glad this has come up also, I have retighten the bolts several times, but never removed and greased them.

Would you guys recommend using a thread locker and which kind should I use? Blue?

And is 42 nm torque the desired tightening value with the thread locker?

Thank you.

[EddyQ]

I'm glad this thread came to the surface again. My bike was only three years old the last time I saw this thread; now it's seven years old, and I still haven't disassembled my centerstand to re-grease the pivots. Now I know what's next on my to-do list...

 

Same here . . .

[lkraus]

I've been intending to tackle this for a couple years. Every time I look at it, I realize the entire exhaust system has to come off before I can get a wrench on the center stand bolts. (This little step is not mentioned on the RepROM.) So I just look it over, give it a wiggle, cuss out the engineer who did not put the bolts on the other side, and think, "Maybe next time..."

[Bernie]

Larry, you should at least check the tightness of the bolts. With the bike on the side stand, you can get a 6mm allen wrench into the bolt from the exhaust side and then you can use a 22mm open end wrench on the bushing face from the outside to tighten the bushings.

On my RT, the right side is the only side that ever comes loose.

[Joe Frickin' Friday]

I've been intending to tackle this for a couple years. Every time I look at it, I realize the entire exhaust system has to come off before I can get a wrench on the center stand bolts. (This little step is not mentioned on the RepROM.) So I just look it over, give it a wiggle, cuss out the engineer who did not put the bolts on the other side, and think, "Maybe next time..."

 

I haven't looked, but does the exhaust really have to come completely off? To remove the rear wheel (as for a tire change), the exhaust has to swing out of the way, and I would have thought this would also be enough to access the centerstand's left pivot bolt. Swinging it out of the way is relatively easy: one hanger bolt comes off (near left passenger footpeg), and then loosen the clamp bolt upstream of the silencer. Wiggle a bit as you twist the silencer down and the left.

 

Does/Would this not give you the access you need for the centerstand?

[Indy Dave]

I've been intending to tackle this for a couple years. Every time I look at it, I realize the entire exhaust system has to come off before I can get a wrench on the center stand bolts. (This little step is not mentioned on the RepROM.) So I just look it over, give it a wiggle, cuss out the engineer who did not put the bolts on the other side, and think, "Maybe next time..."

 

I haven't looked, but does the exhaust really have to come completely off? To remove the rear wheel (as for a tire change), the exhaust has to swing out of the way, and I would have thought this would also be enough to access the centerstand's left pivot bolt. Swinging it out of the way is relatively easy: one hanger bolt comes off (near left passenger footpeg), and then loosen the clamp bolt upstream of the silencer. Wiggle a bit as you twist the silencer down and the left.

 

Does/Would this not give you the access you need for the centerstand?

 

unfortunately, that section of the exhaust is aft of the center stand. Here you can see the location of the 6mm bolt Bernie was mentioning. The second photo show the forward mounting point of the center stand - but I don't believe those are suspect?

 

BTW - My bolts were tight.

 

[/img]

[Bernie]

I was able to reach both bolts without having to remove or drop the complete exhaust system. Just dropping the cannister would not provide any extra room.

Of course if you try to get a socket with a torque wrench on the allen bolt, you would have to drop the complete exhaust system, to make room.

Or you maybe able to use a 22mm crowfoot socket to torque the bushing and hold the bolt with a l-shaped allen wrench.

I decided to just make it tight, as 42 mn is pretty snug on a small bolt like this one.

But I think I will keep a closer eye on it and start checking my bolts with the 6K services. Just my 2 cents.