1000SFC Yoke Bolts

[Laverdalothar]

see - everything will be good at the end... 

 

[CLEMTOG]

I would not ride a bike if I knew it had those yolks fitted to it, save them for posterity and get some "later" ones, ie after #0003

the helicoil repair sounds and looks bad, a waisted bolt (!!!) what kind of engineering lunacy is that, you would'nt pinch your forks with 5mm bolts would you? and bolts that have a safety margin built into them for destruction to protect something else, have a "waist" just like yours, in order to HELP them snap,I would want my pich clamp bolts torqueing not snapping.
welding the yolks through a hole will be difficult (much better to open a slot along its length),
but then the welding will distort and twist the yolk, which will require straigthening, and the temper from the cast alloy will be lost and nearly impossible to replace.

Make some new yolks from billet is what I would be looking to do/get done if useing parts from a previously broken up bike distresses.Why do people lambarst the breakers, and then use second hand parts?

CLEM

 

[Laverdalothar]

Why do people lambarst the breakers, and then use second hand parts?

CLEM

Hi Clem,

there is a difference between using used parts from bikes that are destroyed or beyond economic repair and braking perfect, original and runnig low-millage bikes to be able to sell maybe 20-35% of it...

I am not a metal expert, but would expect typically that a weld is stronger than a casting, no? Scott will find out soon, as when he tightens the bolt with a torque wrench, he will see if it will be able to stand the 60 Nm that are roughly necessary to fix the thing. If he can go up f.e. to 65Nm, there is enough strength in that thread. And no, he will NOT be making the bolt like it was. With the welded up and re-drilled seat, he will be able to use a standard M10 bolt.

This bike is something special as it is the first ever production RGS 1000 SFC. Keeping it original as much as possible is keeping its collectors value. Second to that, even if the upper yoke will give up and crack, the lower yoke will keep the fork-leg mostly in place to make you able to stop safely.

Sure your solution (new yokes made out of billet alloy) would be the best solution in terms of strength. Second to that would be the used parts I have here, but I understand Scott's decision and would go for it maybe, too, as I don't think it will be weaker than the solution that was built in - and that worked, too, at least for a while...  

 

[Grant]

The weld is stronger than the alloy, then the repair breaks adjacent to the weld as that is weakened.

 

[laverdakeith]

Interesting solution Lothar, tighten it up until it strips then back it off half a turn....

Welded repair will be fine, if done properly there will be no distortion as the weld is local and only plugging a hole.



    Keith

 

[Laverdalothar]

Interesting solution Lothar, tighten it up until it strips then back it off half a turn....


    Keith

that was not exactly what I said... I said if it holds at 65Nm, it is stronger than required, as that would be 60Nm (or 57? Not sure...). 

 

[Dellortoman]

he is going to fabricate four new bolts with the correct radius cut into the center to make room for the stanchions

Sounds like a crazy solution to me. If he's going to weld up and re-drill/tap the holes, then why not drill the holes in such a position that you don't need to cut a radius in the middle of the bolts.
Unless I misunderstand your solution, it seems that you're re-creating the problem you have now with the waisted bolts.

Cam

 

[andre g]

As This are the upper yokes, I do not see any problem. The load on these is not much.
The lower yokes are more loaded the upper just get horizontal forces.
Andre

 

[Rockitdoc]

Sounds like a crazy solution to me. If he's going to weld up and re-drill/tap the holes, then why not drill the holes in such a position that you don't need to cut a radius in the middle of the bolts.
Unless I misunderstand your solution, it seems that you're re-creating the problem you have now with the waisted bolts.

Cam

The amount of waisting required is very minimal.  The bolts are 10mm.  The amount of intrusion into the stanchion cavity is 0.005-inches (0.127mm).  The 'waist' will be cut along the same radius as the stanchion (41.7mm dia) making the bolt 9.746mm diameter at it's center.  The yield strength of the grade 5 bolts being used is 92ksi (tensile strength at failure is 130ksi).  This means the bolts will yield at roughly 47kN.  So, torquing them to 65N, as Lothar suggests should not stretch them too much.  The weakest link here is the thread strength, not the bolt.  I will work up the thread strength, too, but I bet Laverda got that right when they used the coarse 10mm threads.  So, as a result, I am not concerned about the repair.  However, that does not answer the question about how the castings were originally made, who made them, and what alloy is in the yokes.  I understand these fail occasionally?  

 

[Davo]

Finest Italian Cheesealloy

 

[laverdakeith]

The material the yokes are made from welds nicely, I've repaired a few stripped threads by welding and re machining as you are proposing to do as timecerting involves drilling a large clearance hole through the bolt seat it is the best way to repair, mill the top half of the threaded portion away root out the remains of the thread and get everything nice and clean then re build the area with weld. The failures are usually caused by overtightning, not really a fault with the component.. Ceriani types particularly crack around the bolt seat when tended to by the fists of ham, welded these too 

  Keith

 

[Rockitdoc]

Fists of Ham were certainly around this bike at one time.  Not referring to you, Lothar!  And, it's good to hear the welding is likely going to be successful.

 

[lemonjelly]

I d rather keep it original on the shelf

 

[Dellortoman]

The yield strength of the grade 5 bolts being used is 92ksi  ...
torquing them to 65N, as Lothar suggests should not stretch them too much.  

G'day Rockitdoc

Don't worry about the stretch (axial load) on the bolts. It's the shear stress from the spanner as you tighten them that will break them.


Root diameter of M10 thread is about 8.5mm, let's say you waist the bolts to 8mm.

A torque of 65 Nm  applied to an 8mm dia shaft produces a shear stress of 647 kN.

Your yield figure of 92 ksi = 634 kN. But the shear strength of steel is generally taken to be about 60% of tensile strength, which means your bolt will yield at 380 kN, so it will break long before you get to 65 Nm of torque.

I know a little bit about engineering, but you don't have to take my word for it. The above calculation is borne out by standard torque charts for bolts. http://electronicfilters.tpub.com/TM-10-4330-237-13P/css/TM-10-4330-237-13P_105.htm

I dunno where Lothar got the torque of 65 Nm from. If you look at the torque chart, that's well in excess of normal tightening for even a grade 8.8 M10 bolt (not waisted). It'll tear a grade 5 bolt apart. If you're using a grade 5 M10 bolt waisted to 8mm, you'd be pushing your luck at anything more than about 15 Nm.

I'd strongly recommend you use at least grade 8.8. If you leave them full diameter (also strongly recommended) you can take them to 50 Nm. If you waist them to 8mm don't go beyond 25 Nm. If you waist them any skinnier than 8mm, then you're asking for trouble. There's actually not a lot of point in waisting the bolts. If you're re-drilling and tapping anyway, and can't achieve the clearance for a 10mm bolt, just use a skinnier bolt. The additional strength of a larger diameter thread gives you no advantage if you can't tighten the bolt because it's waisted.

BTW, I don't agree with Andre that the upper triple clamp is only loaded horizontally. When all bolts are nipped up tight, the upper annd lower triple clamps become part of a rigid system, so vertical and torsional loads are distributed across both sets of clamps. If they only had to resist horizontal loads, they wouldn't need pinch bolts at all - they'd just need to be a sliding fit.

Cheers,
Cam

 

[Cosi]

Sounds like crazy talk to me, Stevie B has a luverly billet setup, if your intending on riding it in anger then I'd be shelving it for the rivet counters, but by the sounds of it youve resigned yourself to that class

As you were

 

[Simonr501]

There is nothing wrong with waisted bolts! Some of the poshest bolts/studs available are waisted!
The reason is very practical, it is sooooo much easier to calculate the tensile strength and stretch on a plain surface rather than a jagged one. If you think about it the 8.5mm root diameter of a 10mm bolt is actually at the heart of the strength of the fastener, the rest gives minimal advantage as the weak point is at the thread root.

EDIT: I have just checked my zeus book, a 10mm ISO Metric course thread has a core diameter of 8.16mm.

That said, in this application, the choice of a waisted bolt is very unwise.
The problem is that the bolt thread at the end is larger than the clearance required to the fork tube, if the bolt is not just loosened but totally withdrawn by an unsuspecting operative then the threads will be destroyed on the way out (assuming that they are not alerted by the bolt getting tighter on the way out).  

 

[Laverdalothar]

Guys, maybe I get that wrong here on my side, but I think Scott already decided to weld the wrongly made holes up and re-drill them at the original location so that a non-tapered/waisted screw can be used for all the good reasons you lot mentioned. My feeling is, that he is fully aware of any issue the setup as was could cause in terms of stretch of the screw, strength and forces going into it and their potential causes, hence he want to make a proper repair and decided for the weld and re-drill solution. Considering originality, cost and potential risks, that is the best balance for him I understand, which I agree to, considering his intentions.

So - please take it as given, that the repair will be executed professionally and tested accordingly. So - if it works, it works. If not, Scott will have the second option of putting the thing back on the shelve and take me up on my offer for one of the original, later series sets of yokes.

Cosi's tip regarding SteveB's indeed VERY nice billet yokes is good, but does conflict with Scott's intention to keep the bike as original as possible in a hard to accept way. This bike is to be ridden, but I doubt Scott will race it. So - at the end, it comes down to normal road usage forces, which the repair for sure will be strong enough for.

So - summing all options up with pros and cons, you will find 3 options basically:

A) repair of the original yoke. Pro: cheapest repair, closest to original. Con: potential risk of weakening the rest of the material to a grade where it could potentially snap. Chances are minimal though if done right, as confirmed by our expert Keith.

B) replacement with the original yokes I have. Pro: close to original, bolt-on-solution. Con: cost of goods and shipping higher, not fully original anymore

C) SteveB's brilliant billet yokes. Pro: probably the stiffest and nicest yokes for that bike available, right dimensions, bolt-on solution. Cons: delivery time is currently a bit longer, price is roughly 3 times the price of a set of used yokes from me and it is far, far away from original, which - I assume - makes it a no-go for Scott.

Anything missing?

At least we are staying on topic

 

[sfcpiet]

Normal torquing value for a steel M10 in aluminium would be around 35-38Nm.  A bit more than our M9 engine studs...

65Nm will not only stress the bolt, but it might well pull either the thread or crack the opposing part of the yoke, if the bolt holds up.

Also quite normal, and wise, practise to use coarse theads in soft alloy, results in more engaging surface area than fine pitch threads.

piet

 

[Laverdalothar]

Normal torquing value for a steel M10 in aluminium would be around 35-38Nm.   A bit more than our M9 engine studs...

65Nm will not only stress the bolt, but it might well pull either the thread or crack the opposing part of the yoke, if the bolt holds up.

piet

Might be I had the torque values from the Telefix Clip-ons in mind, which have the same M10 screw, also sitting in an alloy casting. see: http://www.telefix-products.de/attachment.php?id_attachment=72

6Kp/m => 59Nm

 

[Davo]

So - please take it as given, that the repair will be executed professionally and tested accordingly. So - if it works, it works. If not, Scott will have the second option of putting the thing back on the shelve and take me up on my offer for one of the original, later series sets of yokes. bouncing down the road on his head.

Fixed