Rear Sprocket bolts all sheared off

[Mobius]

1) Turn the sprocket back the right way and get a proper spacer made to go between the sprocket & carrier.

This is a winter time job I think. But it is much more complex than simply doing that, as CB discovered with his D250. I'll see how this works, and if it doesn't break, I won't mess with it.

2) Check the alignment between front & back sprockets. Anything over 1mm needs attention.

It's 2mm. Engineers I have spoken to outside of this forum, including a guy who worked with chains for 20 years says "2mm over a reach that long is a non-issue."

3) Loose the washers.

I think loose washers isn't such a good idea. I'll just not use any at all.

Thanks everyone - for all your input. I have learned several valuable lessons here!

1) Don't just tell a bike shop to do some modification without doing any research first, or at least looking at the parts for myself.

2) Don't trust a bike shop to use an appropriate bolt. It was they who installed the cap-screws instead of bolts with shanks.

3) Don't replace bolts without first checking to see if the bolts are appropriate for the job.

4) Don't use grease on bolts. Use locktite instead.

5) Don't add parts unnecessarily. I added washers. Probably a bad idea.

6) Do use the proper torque wrench to apply the correct torques.

Does that cover it?

[higgy]

2) Don't trust a bike shop to use an appropriate bolt. It was they who installed the cap-screws instead of bolts with shanks.

It is always a good idea to get to know your tech and check all work they do before you ride off into the sunset ( shit happens even to the best of techs)

Cap screws are the proper bolt, if the shankbolts are used and the shanks are longer than the sprocket(or spacer and sprocket) is wide you will strip the threads out of the carrier...not good
A few additional comments after taking 3 different 906 rear wheels apart

1) the bolt holes in the sprocket have absolutely nothing to do with your failure. The fact that you did not torque them is why they failed, nothing more to it than that. All three wheels had cap screws of medium strength, no shanks. Three different sprockets, two had the standard recess,one had none. Not one of the sprockets fit any where near tight to the capscrews

2) It is the clamping force provided by the cap screws along with a tight fitting center hole of the sprocket to the carrier that keeps the sprocket from shearing the bolts. The center hole centers the sprocket not the capscrews to the carrier. Now if you install a sprocket with out a tight fitting center hole you will need some other way to center the sprocket to the carrier

3) safety wiring will not in itself keep the bolts torqued properly, It may or may not keep them from falling out, if the bolts come loose enough to allow the bolts to shear it will make it easier to find the sheared off heads as they likely will still be wired together It does however look good

4) in order to use a larger bolt, you will need a different nut but it can be done without modifying the carrier.
It would also have the side benefit of being a taller style nut which would fit the carrier better and make assembly much easier and most likely stay torqued longer

[Mobius]

All, ship-shape now I think. Odd for a motorcycle I know.

[paso750]

looks somehow like before, doesn`t it ? With a few additional holes
Are those bolts 8.8 or 10.9 grade ?

G.

[giocast]

What a shame.. pretty well knew this would happen...

Cap screws are the proper bolt

but bolts with a shank are FAR better

1) the bolt holes in the sprocket have absolutely nothing to do with your failure. The fact that you did not torque them is why they failed, nothing more to it than that.

complete and utter twoddle.

2) It is the clamping force provided by the cap screws along with a tight fitting center hole of the sprocket to the carrier that keeps the sprocket from shearing the bolts.

I don't know if this Forum has a swear filter but I feel strongly enough about this subject that I am happy to risk a ban - You are talking Bollocks Higgy and I think you're out of your depth here mate - if you want to compare credentials in a P.M. then i'm up for it son! It's this sort of mis-information that usually ends in me not posting anymore, so you will win in the end, no doubt about it.

[higgy]

What a shame.. pretty well knew this would happen...
higgy wrote:

Cap screws are the proper bolt
but bolts with a shank are FAR better
higgy wrote:
1) the bolt holes in the sprocket have absolutely nothing to do with your failure. The fact that you did not torque them is why they failed, nothing more to it than that.
complete and utter twoddle.
higgy wrote:
2) It is the clamping force provided by the cap screws along with a tight fitting center hole of the sprocket to the carrier that keeps the sprocket from shearing the bolts.

I don't know if this Forum has a swear filter but I feel strongly enough about this subject that I am happy to risk a ban - You are talking Bollocks Higgy and I think you're out of your depth here mate - if you want to compare credentials in a P.M. then i'm up for it son! It's this sort of mis-information that usually ends in me not posting anymore, so you will win in the end, no doubt about it.

Bolted Joint Design

Introduction

A most important factor is machine design, and structural design is the rigid fastening together of different components..This should include the following considerations..

* Assembly
* Accuracy of positioning
* Ability to Hold components rigidly together against all forces
* Requirement to separate components
* Retention of fastening over time

There are many methods of fastening items together including

* Bolting
* Rivetting
* Pins
* Keys
* Welding/Soldering/Brazing
* Bonding
* Velcro
* Magnetism


These notes relate primarily to the bolted joint. The bolted joint is a very popular method of fastening components together. The prime reason for selecting bolts as opposed to welding, or rivets is that the connection can be easily released allowing disassembly, maintenance and/or inspection..

The bolts /screws are generally used in groups to fasten plates together. A bolt is a screwed fastener with a head, designed to be used with a nut. A screw is a fastener designed to be used with a formed female thread in one of the components being attached.

These notes generally relate to bolts and nuts and hex headed screws..

Bolt loading

A bolt can be loaded in one of three ways

* Tension
* Shear
* Combined Shear and Tension

Note: Conditions where bending loads are imposed on the bolt e.g. non-parallel bolting surfaces, should be avoided.

A bolt is primarily designed to withstand tensile loading while clamping components together. Ideally the bolt should only be loaded in tension. Any forces tending to slide the clamped components laterally should be withstood by separate means..

Holes for bolts are generally clearance holes and the best design of bolt is one with a reduced shank diameter (waisted shanks). Joints in shear depending on the bolts to withstand the shear load are not really rigid. Significant relative sideways movement must take place before the bolt shank can take any shear load (hole clearance). It is also likely that in the case of components attached by a number of bolts that one bolt would be loaded first and this bolt would have to yield before the other bolts take their share of the shear load....

Bolts taking significant tensile and shear load need to be engineered to withstand the combined stress..

In structural engineering the codes identify the use of High Strength Friction Grip Bolts (Ref BS 4604 Pts 1-2:1970). The bolts are tightened to a specified minimum shank tension so that transverse loads are transferred across the joint by friction between the plates rather than by shear across the bolt shank.

In mechanical engineering / machine engineering, items are often accurately located using dowels /locating pins. When installed these dowels /locating pins should be engineered to withstand any traverse loads. A recent innovation is to provide dowel bushings. These are used in conjunction with bolts which pass through the inside of the bushing after it has been installed. Separate holes for locating pins are eliminated. The hardened bushings absorb shear loads, isolating the bolts from these forces.

If the choice is made that bolts/screws are to take shear load the joint should be arranged that the threaded portion of the bolt/screw shank is not taking the shear.
The notes on this page relate to the mechanical engineering industry.. In the aerospace industry joints are often designed to specifically load the bolts in shear. The screws and bolts used are high specification close toleranced items and the holes are also machined to close tolerances. The bolted lap joints are generally used for critical assemblies and joints designed with bolts loaded in tension are avoided.????


Strength of Bolts in Shear

Important Note:
The calculations below are based on the unrealistic assumption that there is no friction forces between the plates which are clamped by the bolts. The calculations are therefore conservative (safe)..
Strength of Bolts withstanding direct shear loading

For bolts joints loaded in shear - three stress areas result-

* The bolts are loaded in shear..Depending on the joint design the bolt can be in single or double shear...
* The bolt interface with the hole is compressively loaded. ( Crushing )
* If the hole is near to the edge of the plate the plate is subject to shear loading

Single Shear..

Shear Stress = 4 . F / π. d 2
Compressive Stress = F / (d . t)
Plate Shear Stress = F / (2.c.t)

Double Shear ..

Shear Stress = 2 . F / π. d 2
Compressive Stress = F / (d . t)
Plate Shear Stress = F / (2.c.t)

The stresses are adjusted based on the number of bolts / screws used for the joint..
Strength of bolts withstanding torsion generated shear loading

Consider a bracket taking an offset load F (N) at a radius R (m). The bracket is secure using a number of bolts each with a Area A(m2 ). The bolts are located around a centroid position each with a radius from the centroid of rn(m) and a horizontal/vertical position relative to the centroid of hn /vn (m) . ( bolt is designated by the subscript "n". )


Location of Centroid...
The location of the centroid of the bolts can often be determined by inspection as in figure above. If the bolts are not arranged around a convenient centre then the centroid is determined by ..
x position = sum of the moments of area of all the holes about a fixed horizontal position divided by the total hole area
y position = sum of the moments of area of all the holes about a fixed vertical position divided by the total hole area


The offset load is equivalent to a vertical force (F) + moment (F. R) at the centroid of the bolts...

Each bolt is withstands a vertical shear force Fnv = F / No of Bolts.
Each bolt also withstands a shear load Fnm = F.R. rn / (r12 + r22...rn2)
The total horizontal force on each bolt Fth= Fnm . vn / Sqrt(hn2 + vn2 )
The total vertical force on each bolt Ftv= Fnv + Fnm . hn / Sqrt(hn2 + vn2 )
The total shear load on each bolt Ft= Sqrt (Fth2 + Ftv2)
The resulting bolt shear stress τ t = Ft /A


The shear stress in each bolt is calculated to ensure the design is safe..
Strength of bolt joints withstanding bending forces

Each Bolt withstands a shear Force Fs = Fv / (Number of bolts)
The resulting shear bolt stress τ n = Fs /A

Note: Each bolt is assumed to withstand the same shear force.

If there are x bolts( numbered n = 1 to x). Then the tensile force withstood be each bolt is designated Fnt i.e F1t,F2t, F3t....Fxt
A selected bolt (n) withstands a tensile force of Fnt = ( Fv. Rv + Fh. Rh) . Vn / (V12 + V22....Vx2 )
The resulting tensile bolt stress sn = Fnt /A
Maximum principals stresses in the bolt resulting from combined loading

The notes on this page Assuming all stresses developed only as a result of bracket loading i.e zero preload and zero residual bolt torque...

Maximum principal tensile stress in the bolt

Maximum principal compressive stress in the bolt

Maximum shear stress in the bolt

Failure criteria: Refer to page Failure Modes

The notes on this page In order to estimate the design factors of safety it is necessary to consider the failure modes. The preferred failure criteria for ductile metals is the "Shear Strain Energy Theory" (Von Mises-Hencky theory). For a stress regime associated with a bolt i.e pure tensile stress sx combined with shear stress τ xy. The Factor of safety relative to the material tensile strength Sy..is calculated as follows

Factor of Safety = Sy / ( sx2 + 3 .τ xy2 ) 1/2
Preloaded Bolts : Refer to page Preloading

These stresses do not include for the stresses developed in preloading the bolts. The residual shear stress from bolt tightening should also considered (added). The actual tensile preload force should be considered following the principles identified on the pages addressing this topic

Dude, All you need to do to show me wrong on this is produce one single picture of a 906 that came from the factory with a shank style bolt used to locate the sprocket to the carrier. I took 3 different 906 carriers apart in an effort to help Mobius find the cause. Now it may be that my 3 are some sort of fluke and other possibilities are certainly possible OK show me My only point here was it was not the style of bolt Mobius chose that caused his carrier to come apart. It was the fact that he neglected to torque them properly regardless of the bolt the used. It also appears to me that at this point the factory for whatever reason chose to use the same style of bolt used every where else. Nothing more was intended or implied. I do however till such time as you or anyone else can show me different in this case stand by what I stated

But proper torque for the bolt is key!

I have absolutely no interest in getting into a pissing contest here. I am most definitely not your son, sonny boy


Giocast, no reason for you to get a gander up, there is plenty of room here for all of us and discussion is all part of it. I for one would hate to see you go

[Tamburinifan]

higgy wrote:
1) the bolt holes in the sprocket have absolutely nothing to do with your failure. The fact that you did not torque them is why they failed, nothing more to it than that.

higgy wrote:
2) It is the clamping force provided by the cap screws along with a tight fitting center hole of the sprocket to the carrier that keeps the sprocket from shearing the bolts.

So what is the correct info on this according to your knowledge, giocast?

[giocast]

Not even answering you yet Higgy as i'm still calming down.. Tamburinifan - I layed out all my thoughts in an earlier post - at the risk of wasting my time again (not talking about you T.F.) I can P.M. you with more info if necessary.

[higgy]

No problem Take your time, Mobius is on the road I for one as well as others here do enjoy a spirited discussion


There is a wealth of interesting reading on the subject here http://www.eng-tips.com/threadminder.cfm?pid=725

[higgy]

Gert,
The correct answer is the torque applied.

The style of bolt is a non issue unless of course you want to keep the bike as it was originally delivered. The style of bolt you use aside from that one issue is of course open to debate. In the end it comes down to the clamping force applied between the sprocket and the carrier. Bolts are not intended to locate anything or resist shear forces by them selves beyond the torque they apply, at least not outside of an aerospace application or possibly Formula racing where the need to keep things as light as possible is the main goal and not "generally acceptable and reliable engineering practice."
Outside of that it is always better to use a pin(s) to locate the sprocket and resist a failure due to improper torquing (or misalignment before torque is applied). It is simply a matter of good engineering practice especially when it comes to aluminium/steel combinations.
One additional note about using Loctite, when you use it you can not retorque the bolts or check the torque once the loctite is set,can be a good thing,but also can be a bad thing.

PS The issue with the Nordlock style washers comes down to the fact the washers are generally softer than the metals they join.

PSS you think I pissed off anyone else ?

[giocast]

PSS you think I pissed off anyone else ?

you obviously know how to use a spoon you little dear, but I think I ought to post you a spade because despite being a seasoned member on here, you will never earn total respect if you keep 'fanning the flames' as above. Life too short for me to continue defending what I know to be true. I refer all readers (those who GAF!) to my earlier post addressed entirely to you.

[higgy]

you obviously know how to use a spoon you little dear, but I think I ought to post you a spade because despite being a seasoned member on here, you will never earn total respect if you keep 'fanning the flames' as above. Life too short for me to continue defending what I know to be true. I refer all readers (those who GAF!) to my earlier post addressed entirely to you.

P.H.D.

Hex cap screws

ASME standard B18.2.1 -1996 specifies Hex Cap Screws that range in size from 0.25–3 in (6.35–76.20 mm) in diameter. These fasteners are very similar to hex bolts. They differ mostly in that they are manufactured to tighter tolerances than the corresponding bolts. The Machinery's Handbook refers parenthetically to these fasteners as "Finished Hex Bolts".[9] Reasonably, these fasteners might be referred to as bolts but based on the US government document, Distinguishing Bolts from Screws, the US government might classify them as screws because of the tighter tolerance.[10] In 1991 responding to an influx of counterfeit fasteners Congress passed PL 101-592[11] "Fastener Quality Act" This resulted in the rewriting of specifications by the ASME B18 committee. B18.2.1 [12] was re-written and as a result they eliminated the "Finished Hex Bolts" and renamed them the "Hex Cap Screw".

Until such time as anyone shows me evidence to the contrary The HEX CAP SCREW is what came from the factory..

Now here is another observation.. The carrier is threaded for a larger size bolt. For some reason At least on the 3 906 Paso's I took apart which btw came from 3 different countries. What ever the style (bolt/screw) was intended for these carriers was replaced with a socket head cap screw of the same quality used on other assemblies on the 906 and a nut installed .
One sprocket is still factory,the other two I can't say, however dimensionally they are the same other than two of them have no recess for the "bolt/screw"

One more question for you Giocast, Not meant to inflame or insult,just a question out of curiosity.Please don't read into it.........Get that bike running yet? What turned out to be the issue ?

Anyway I think this topic has been beat to death
Out of curiosity What type of fastener holds other 906 carriers together here? Anyone?

[Mc tool]

not to sure who is really fanning the flames here ( or perhaps waving a spade at them ) , but Higgy most certainly has my respect , and appreciation ( webberology is brilliant ), as do others here. I guess that when you get two ( or more ) experianced , clever guys from opposite sides of the world and put them in the same room , any discussion re their passions is bound to expose a difference of ( very good ) opinions, and long may it continue If we all agreed with each other we would still be living in caves and dragging women round by their hair ( I like that bit )
Love to all

[giocast]

Life too short for me to continue defending what I know to be true. I refer all readers (those who GAF!) to my earlier post addressed entirely to you.

[higgy]

No worries Mctool, its all in good fun.
and if it keeps even one more Paso from the parts sections of ebay it is well worth it



but then again,there are a few parts I need from time to time


btw, our Dyne is on the way so the final chapter of weberology should get underway soon..anyone got a line on a pair of F27's or a cheapo 750?


Hey Gio, wtf is GAF? This side of the pond it refers to "gay ass fag" Something you need to take outta the closet,.....buddy