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Yeah, we've seen that. Does your manual show this?




I believe that is referring to these:




The text for the section on removing the headers on the Bonnie confirms that those bolts marked above should be at 27Nm.

But can't find anywhere the torque listed for the clevis bolts. It's listed as 45Nm for the America, but nothing for the Bonnie in my manual. Passenger ones are listed as 27 Nm in the later chapters. I assume the bolts are 27 Nm as well. I had just assumed that when you did your closed form equations to determine that this joint was properly engineered that this torque value would have come up, and hoped you remembered.

My gut instinct, it does seem like 45 Nm is too high for that bolt, but that's just a gut instinct.
No, I have not calculated the tension in the bolt. I'll have to do a little research to find out the diameter and grade of this fastener. If memory serves, the suspect fastener is an M8. My Unbrako engineering guide recommends a seating torque of 35 Nm. Bear in mind that this is for a high toughness, high strength heat treated steel with a minimum yield stress of 940 MPa. This is probably a considerable upgrade to the bolts used on our Triumphs. So, a torque of 27 Nm looks reasonable to me. 45 Nm appears to be way too high.

With a torque of 35 Nm (310 lbf in) an M8 bolt (diameter 8mm or 0.315 in) and "K" value of 0.20, the preload on the fastener holding the two brackets together is over 4,900 lbf. I think that you can see that if the torque is not to recommended value, the preload will be considerably less.

My manual shows the torque for the Footrest to outrigger locknuts as 27 Nm for the Bonneville, Bonneville SE, and Bonneville T100. It shows 40 Nm or 45 Nm for the Outrigger to frame bolts depending on whether they are silver bolts or black bolts
 

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for Bonnies the riders footrest bolt is an M8, the same as the passengers. the FSM on page 1.43 and pg 9.42 nominate 27 Nm for the passengers so I think it safe to assume that would also be correct for the riders

27 Nm cross referenced to bolting torque charts suggests a property class of 8.8 with the the fastener torqued or tensioned to about 70% of its "proof" or tensile strength.

so there is an opportunity to upgrade to an 'Unbrako' low head capscrew. Unbrako fasteners have a greater property class and therefore can carry a higher load without the need to increase bolt diameter

70% of the strength of the bolt used in tensioning may sound like there isn't much strength left to carry the load of the rider, however as a bolt is tightened the mating surfaces of the joint are loaded up with compressive forces and therefore most of the load from the rider is carried by the joint faces, not the bolt

if the bolt torque, or pre-tension is reduced the compressive forces on the joint is also reduced and the riders load is therefore carried by the bolt. it is this reason why fatigue failures are often associated with low pre-tension

mating surfaces are important and I agree the existing surfaces are not ideal, but I think the underlying cause and most important factor is correct tension of the bolt. in other words a loose bolt aint going to support your weight
 

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Discussion Starter #83
So the design is perfect, as is, and doesn't need to be looked into? Then, the solutiin is for Bonneville owners to check for proper torque before every ride? Or, is there room for improved design that has.a better fail safe and reduces the chance for operator error? The current design might be good enough in theory, but, the reality of the situation is that there are many cases of them breaking. That's why I started this thread.
 

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Most Bonneville rides will never read this,so best of luck to all of them ! If this would ever cause a deadly crash the chances are no one would ever know what caused it.More than likely they would think the peg broke off in the accident. Yes they're MANY better designs than this one. Like on every bike I have ever owned before this one.
 

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Yes they're MANY better designs than this one. Like on every bike I have ever owned before this one.
I've been casually observing footpeg mountings for ages now, sad, I know, but the Bonnies is the weakest one I've seen so far. The only similar arrangement, on an Aprilia, uses an M10 bolt.

Triumph already make a fine all-in-one piece outrigger and clevis like on the Scrambler:



In case you think that Triumph expect people to stand on the footpegs because it's a kind of dirt bike, there's the Thruxton:



The only other Triumph (The Sprint) with a similar design of separate clevis has a much better arrangement, take a look at the Sprint where not only the clevis bracket has a wide shoulder on it that takes the load, but it's held with an M10 rather than an M8 bolt:

Parts 7 and 30 and bolts parts 29 (M10x30)

http://www.worldoftriumph.com/triump...block_03=10166

Can't find a picture of the Sprint's pegs but these LSL ones are made with the same raised bush part that goes through the outriggers as the OEM ones, you can see the superior design:

 

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So the design is perfect, as is, and doesn't need to be looked into? Then, the solutiin is for Bonneville owners to check for proper torque before every ride? Or, is there room for improved design that has.a better fail safe and reduces the chance for operator error? The current design might be good enough in theory, but, the reality of the situation is that there are many cases of them breaking. That's why I started this thread.
no. I'm not saying the design is perfect. just highlighting the importance of correct bolt tension that this design requires.

I would check it periodically. and do, but if it's tensioned correctly and the bike has not been in an incident should be ok

an easy upgrade would be to change the bolt to an Unbrako low head capscrew, and the designs used on the Thrux and Scram as Forchetto shows are far superior
 

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for Bonnies the riders footrest bolt is an M8, the same as the passengers. the FSM on page 1.43 and pg 9.42 nominate 27 Nm for the passengers so I think it safe to assume that would also be correct for the riders

27 Nm cross referenced to bolting torque charts suggests a property class of 8.8 with the the fastener torqued or tensioned to about 70% of its "proof" or tensile strength.

so there is an opportunity to upgrade to an 'Unbrako' low head capscrew. Unbrako fasteners have a greater property class and therefore can carry a higher load without the need to increase bolt diameter

70% of the strength of the bolt used in tensioning may sound like there isn't much strength left to carry the load of the rider, however as a bolt is tightened the mating surfaces of the joint are loaded up with compressive forces and therefore most of the load from the rider is carried by the joint faces, not the bolt

if the bolt torque, or pre-tension is reduced the compressive forces on the joint is also reduced and the riders load is therefore carried by the bolt. it is this reason why fatigue failures are often associated with low pre-tension

mating surfaces are important and I agree the existing surfaces are not ideal, but I think the underlying cause and most important factor is correct tension of the bolt. in other words a loose bolt aint going to support your weight
Nice, well written, easy to understand post. You have provided some thought provoking information.
 

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Not that I recommend this for everyone, but I removed the bolts holding the outrigger to the bike and that let me get a torque wrench onto the footpeg nuts (and they were OK).
Ah, of course. I can't think of another way to do it besides this method. Thanks.


Sent from Motorcycle.com App
 

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so there is an opportunity to upgrade to an 'Unbrako' low head capscrew. Unbrako fasteners have a greater property class and therefore can carry a higher load without the need to increase bolt diameter

70% of the strength of the bolt used in tensioning may sound like there isn't much strength left to carry the load of the rider, however as a bolt is tightened the mating surfaces of the joint are loaded up with compressive forces and therefore most of the load from the rider is carried by the joint faces, not the bolt
Cool, consensus is on the 27Nm, I can buy that. So, if one were to change to an Unbrako would you continue to torque to 27Nm, which would still meet the load requirements of the joint and leave a larger % of it's capacity to carry any rider load?

Are these a Home Depot type product? All I've found online are packs of 200.

Even if this joint is properly engineered to the conditions it's designed for, and those conditions are sufficient to cover real life usage, and the engineer's design was adhered to, and there are no QC problems in the supply chain or assembly process, there are enough failures for me to think taking some action wouldn't be silly.

Under-torque causing some of these failures makes sense to me. What worries me is that possibility that the bike being on it's side can cause a silent condition where the bolt is weakened without snapping immediately, and putting the rider at risk down the road at some point.

Now, these joints apparently should be designed to take 400 lbs. The bikes weigh about 550 lbs, if if he bike is on it's side not all the weight is on that joint. It's hard for me to believe that a simple parking lot drop is a good enough excuse for the joint to fail down the road at some point.

But my bike's been on it's side twice. Once in the shop when I didn't handle taking it off the jack properly, and once for reasons I won't share. But I no longer make fun of people who forget to put their kickstands down at gas stations.

So, I suppose I should do something. I'm not just going to replace my footpegs with new OEM ones, I don't trust the design/implementation of the joint enough. If I'm going to pull the footpeg brackets re-check the torque I might as well as replace the bolt with a stronger one and throw some loctite on the threads while I'm in there. I might add that to my winter maintenance list.
 

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Unbrako socket head cap screws are usually sourced from industrial engineering suppliers

as they are property class 12.9 they would need to be torqued to 43Nm to give the desirable clamp force, which obviously would be a lot greater than the stock bolts.

knowing the property class (and diameter) is essential to determine the correct torque value

it would pay to confirm the property class of these if purchased as sometimes metric screws are supplied in property class 10.9 and the torque value then should be 38Nm. something to do with euro standards versus US standards (its complicated)

5/16" is very very close to 8mm and that size could be used instead. inch size unbrakos are always supplied to 12.9 and can be safely torqued to 43 Nm

and it has to be a low head capscrew as normal headed capscrew is too tall and will not fit between the clevis and peg

remember that torquing to the correct specification takes the load off the bolt by about 80-90% thus transfering and distributing the load to the joint. under tensioning places more load on the bolt
 

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Cool, consensus is on the 27Nm, I can buy that. So, if one were to change to an Unbrako would you continue to torque to 27Nm, which would still meet the load requirements of the joint and leave a larger % of it's capacity to carry any rider load?

Are these a Home Depot type product? All I've found online are packs of 200.

Even if this joint is properly engineered to the conditions it's designed for, and those conditions are sufficient to cover real life usage, and the engineer's design was adhered to, and there are no QC problems in the supply chain or assembly process, there are enough failures for me to think taking some action wouldn't be silly.

Under-torque causing some of these failures makes sense to me. What worries me is that possibility that the bike being on it's side can cause a silent condition where the bolt is weakened without snapping immediately, and putting the rider at risk down the road at some point.

Now, these joints apparently should be designed to take 400 lbs. The bikes weigh about 550 lbs, if if he bike is on it's side not all the weight is on that joint. It's hard for me to believe that a simple parking lot drop is a good enough excuse for the joint to fail down the road at some point.

But my bike's been on it's side twice. Once in the shop when I didn't handle taking it off the jack properly, and once for reasons I won't share. But I no longer make fun of people who forget to put their kickstands down at gas stations.

So, I suppose I should do something. I'm not just going to replace my footpegs with new OEM ones, I don't trust the design/implementation of the joint enough. If I'm going to pull the footpeg brackets re-check the torque I might as well as replace the bolt with a stronger one and throw some loctite on the threads while I'm in there. I might add that to my winter maintenance list.
I don't intend to make any modifications to the stock foot peg bolts on my T100. That seems like unnecessary overkill. Checking the torque; however, is a pretty easy thing to do. I plan to do that the next rainy day that I have without a lot of "honey do" projects that have higher priority.
 

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I don't intend to make any modifications to the stock foot peg bolts on my T100. That seems like unnecessary overkill.
I hear you. Doing it meets my internal risk/reward/cost/benefit requirements, YMMV. But I can't say I'm stressed over the issue or will stay off my bike until it's done. At least I haven't gotten to the point of indexing my plugs ... yet.


Unbrako socket head cap screws are usually sourced from industrial engineering suppliers
Fastenal carries Holo-Krome 12.9 grade low head cap screws, they as good as the Unbrako's you're recommending you reckon? I think they'll sell me two instead of a bag of 100.

Fastenal's site shows a note on the product: "Low Socket Heads are high strength, precision fasteners that are designed to be used in applications where head height clearance is a problem. Because of their reduced head height and smaller socket size, they normally cannot be preloaded as high as a standard socket head cap screw." That gives me pause, maybe back off from the 43Nm preload a bit?
 

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I hear you. Doing it meets my internal risk/reward/cost/benefit requirements, YMMV. But I can't say I'm stressed over the issue or will stay off my bike until it's done. At least I haven't gotten to the point of indexing my plugs ... yet.




Fastenal carries Holo-Krome 12.9 grade low head cap screws, they as good as the Unbrako's you're recommending you reckon? I think they'll sell me two instead of a bag of 100.

Fastenal's site shows a note on the product: "Low Socket Heads are high strength, precision fasteners that are designed to be used in applications where head height clearance is a problem. Because of their reduced head height and smaller socket size, they normally cannot be preloaded as high as a standard socket head cap screw." That gives me pause, maybe back off from the 43Nm preload a bit?
I would use the manual's recommended 27 Nm.
 

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I hear you. Doing it meets my internal risk/reward/cost/benefit requirements, YMMV. But I can't say I'm stressed over the issue or will stay off my bike until it's done. At least I haven't gotten to the point of indexing my plugs ... yet.




Fastenal carries Holo-Krome 12.9 grade low head cap screws, they as good as the Unbrako's you're recommending you reckon? I think they'll sell me two instead of a bag of 100.

Fastenal's site shows a note on the product: "Low Socket Heads are high strength, precision fasteners that are designed to be used in applications where head height clearance is a problem. Because of their reduced head height and smaller socket size, they normally cannot be preloaded as high as a standard socket head cap screw." That gives me pause, maybe back off from the 43Nm preload a bit?
yes, I would use Holo Krome if they are available

and you correct about a lower torque for low head capscrews
unbrako recommends a torque value of 35 Nm for these.

BTW I'm not stressed over the issue either. just make sure my peg bolts are tight. but I do refrain from standing on the pegs now.
 

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No , you want to torque to the bolts spec, not the bike. This is a really small diameter bolt for this application. In fact, nothing I have ever owned has used this small bolt diameter for a footpeg. Even my 125 Honda has bigger footpeg bolts. So that is the main problem. The bracket is also garbage, and yes I'm referring to the curve. A manufacturing shortcut that compromised the strength of the bracket to save a buck. Larger bolts and a new flat bracket is the cure. That said, the minimum I would do is replace the bolts with at least 8.8 if not stronger. The redundant bolts is also a great idea. Leaving this problem alone and waiting for a factory recall is not something I would do. I do stand on pegs from time to time, and to have one break at an in opportune moment is not something I wish to experience.
 

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Thanks bonza.

but I do refrain from standing on the pegs now.
I'm on my pegs a fair bit. When I have camping stuff on the back the only way to get on her is to get up on one of the pegs and kick the other leg over. On rough patches of dirt road gotta get up on the pegs and let the bike rotate as it will under me. And of course, avoiding spinal compressions on potholes. Gotta admit, I think of this issue every time.
 

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I'll just add for those considering low head cap screws. the head height for these in M8 is 5mm. the existing screw has a measly head height of 2mm

some have mentioned 10mm screws. the head height for these is 6.5mm and they could squeeze in ok if the peg clevis or socket head is filed down slightly and the bolt hole is drilled out. the head diameter is 16mm so there is plenty of room in the clevis. this would add considerable strength as the torque setting is 70Nm for these

alternatively you could use 3/8" low head capscrews, they have a head height of 4.9mm and are some where between M8 and M10 and maybe more easy to obtain

the existing bolt hole for the M8 screws are 9mm dia
 

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No , you want to torque to the bolts spec, not the bike. This is a really small diameter bolt for this application. In fact, nothing I have ever owned has used this small bolt diameter for a footpeg. Even my 125 Honda has bigger footpeg bolts. So that is the main problem. The bracket is also garbage, and yes I'm referring to the curve. A manufacturing shortcut that compromised the strength of the bracket to save a buck. Larger bolts and a new flat bracket is the cure. That said, the minimum I would do is replace the bolts with at least 8.8 if not stronger. The redundant bolts is also a great idea. Leaving this problem alone and waiting for a factory recall is not something I would do. I do stand on pegs from time to time, and to have one break at an in opportune moment is not something I wish to experience.
An 8mm bolt torqued to 27 Nm has a clamping force of approximately 3,800 lb (16,890 N).
Unless you are a rhino, why do you think that this is marginal?

Could you provide some kind of engineering rational for you opinion that the bracket is garbage because of the slight curvature of the mating surface?

Did it occur to you that drilling out the brackets to put in additional bolts may weaken the joint?

BTW, having a stronger bolt won't help if it is under torqued.

If you insist on putting in additional bolts or larger bolts, make sure that the bolt shaft does not touch the bracket. In other words, make sure that the holes are 2-3 mm greater diameter than the bolt shaft. Otherwise, you will be asking the bolt to sustain bending and shear loads (not designed to do) in addition to the tension load that this joint was designed for.
 

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Why would the proper torque for a bolt with one set of properties be optimal for a bolt with another set of properties?

I agree with duc on the torque to use. I'll use the one appropriate for the bolt I'm using, not what the bike manufacturer spec'ed for a different bolt. If bonza is correct that the spec'ed torque for that bolt is 35Nm, that's what I'm going to use.

Not sure what the engineering rationale is for using a lower torque. The rationale for using the specified torque is that, it appears, you want to stress the bolt enough that it begins to stretch and so begins to act like a spring, and therefore create proper tension on the nut.

27Nm is 20% lower than the spec'ed 35Nm, so it's not a minor difference. Maybe it's close enough to the optimal torque for the 12.9 grade bolt to be effective, maybe not. With all this emphasis on how critical the torque is, I'm not sure what the point is of double guessing the bolt manufacturer.
 
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