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Author Topic: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback  (Read 6501 times)

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Online Welsh

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #40 on: February 11, 2014, 10:38:33 am »

6) DO NOT USE COPPASLIP on this nor on the wheel bolts!

There was a similar spate of rear wheels falling off 1150's they could all be traced, to incorrect torquing (as in not at all) or people using coppa slip on the bolts they should be fitted dry!!!  

I started using copper slip on my rear wheel bolts when I snapped the torx bit trying to remove the wheel.
Previous torque was done when I replaced tires, now I torque my own wheels.
I use very little copper slip and mark the screw when tightened to the correct 60Nm.

Is the 1150 screws also countersunk?

Yes, but only 4 of them, and first torqued to 72Nm then to 105Nm the 1150 is "chunkier"  :biggrin:
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Offline lecap

Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #41 on: February 11, 2014, 11:20:49 am »
I think the bolts dimensions and thread size are chosen a bit unluckily.
An M8 standard thread bolt of grade 8.8 won't stomach much more than 25Nm of torque.
Neither will the corresponding thread in caliper mounting bracket (which I assume is aluminium?)

There is not much of a margin between not tightening these bolts enough and damaging the bolts or threads by over tightening them.
The price you pay for a lightweight bike :-\
There is little margin from the tension on the tightened bolt to its yield strength.
The price you pay for a pencil pushing accountant telling the engineer in the factory that he can only use a standard engineering grade fastener and not the slightly more expensive HT one ::)


If you want to  play it safe you will have to check the bolts for tightness and for correct function of the rear caliper on a regular basis.

Additionally you can fit grade 12.9 HT bolts which have an almost 70% higher yield strength. This should eliminate the possibility of a sticky caliper stretching and loosening the bolts.

I have M8x1.25 x 25mm allen cap screws in HT 12.9 in stock. With very pretty and corrosion inhibiting mil grade yellow cadmium plating for R 10 a pop.

I don't think it's a design flaw. You can not engineer everything to the point that it becomes impossible to break no matter what. You can even break a five pound hammer if you just try hard enough.

If you use liquid thread locking compounds use the correct one. On your bike something like Loctite 242 will usually do the job.
Don't use the high strength varieties like Loctite 271 and 290 unless it's specified and unless you can apply heat for disassembly without causing collateral damage.
When redoing a thread locked connection you have to clean off the old product properly before applying new product and assembling.



Re. the myth or not using of using grease or copper compound on wheel stud nuts or wheel bolts.

It is perfectly fine to use a lubricant on wheel studs or bolts.
The lubrication of the threads serves the purpose to guarantee a constant low torque being required to turn the nut or bolt and achieve the prescribed tightening torque, mostly by preventing corrosion and surface damage.
It also helps to prevent corrosion of the threads.

Reason:
A corroded thread will cause a significant portion of the tightening torque being lost to turning the bolt and not actually tightening (elastically stretching) it.

More important:
Whilst the sliding friction coefficient (which is always quoted because the difference looks oh so impressive) of lubricated steel on steel is only some 20% of the coefficient for dry steel on steel the difference between the limiting friction for lubricated and dry steel to steel (or aluminium) contact is nearly identical.
Sliding friction is irrelevant for breaking loose a tightened fastener.
The limiting friction is all that counts and it is only some 10% to max. 20% lower for a greased fastener as compared to a dry one.

I don't think BMW would only allow for a 10% to 20% safety margin between a wheel and no wheel at the back of your bike ???
How close would the inaccuracy of a standard torque wrench (like 5%) get you to disaster ???
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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #42 on: February 11, 2014, 11:31:37 am »


If you want to  play it safe you will have to check the bolts for tightness and for correct function of the rear caliper on a regular basis.

Additionally you can fit grade 12.9 HT bolts which have an almost 70% higher yield strength. This should eliminate the possibility of a sticky caliper stretching and loosening the bolts.

I have M8x1.25 x 25mm allen cap screws in HT 12.9 in stock. With very pretty and corrosion inhibiting mil grade yellow cadmium plating for R 10 a pop.


I fully agree, this would be a good idea.



Re. the myth or not using of using grease or copper compound on wheel stud nuts or wheel bolts.

It is perfectly fine to use a lubricant on wheel studs or bolts.
The lubrication of the threads serves the purpose to guarantee a constant low torque being required to turn the nut or bolt and achieve the prescribed tightening torque, mostly by preventing corrosion and surface damage.
It also helps to prevent corrosion of the threads.

Reason:
A corroded thread will cause a significant portion of the tightening torque being lost to turning the bolt and not actually tightening (elastically stretching) it.

More important:
Whilst the sliding friction coefficient (which is always quoted because the difference looks oh so impressive) of lubricated steel on steel is only some 20% of the coefficient for dry steel on steel the difference between the limiting friction for lubricated and dry steel to steel (or aluminium) contact is nearly identical.
Sliding friction is irrelevant for breaking loose a tightened fastener.
The limiting friction is all that counts and it is only some 10% to max. 20% lower for a greased fastener as compared to a dry one.

I don't think BMW would only allow for a 10% to 20% safety margin between a wheel and no wheel at the back of your bike ???
How close would the inaccuracy of a standard torque wrench (like 5%) get you to disaster ???

I cannot find fault with the logic, and particularly at the Coast (had some issues with my car wheels back when I lived in Mossel Bay), however BMW do not recomend it and I would limit it to a small amount, I also believe torquing correctly is the real answer.  8)
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Offline katana

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #43 on: February 11, 2014, 07:59:29 pm »
Unless I missed it, can someone tell me the torque value of said bolts?
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Offline Jondu

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #44 on: February 11, 2014, 08:04:01 pm »
Die versekering betaal darm my skade. Ek is nogal bly,want dit is n R14K werk. Ek sal maar gereeld moet kyk, maar dit maak my maar bekomerd.
 

Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #45 on: February 11, 2014, 08:07:42 pm »
Unless I missed it, can someone tell me the torque value of said bolts?

On my initial post. 24Nm

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Offline Raka

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #46 on: February 11, 2014, 08:39:24 pm »
Unless I missed it, can someone tell me the torque value of said bolts?


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Offline katana

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #47 on: February 11, 2014, 09:08:31 pm »
Unless I missed it, can someone tell me the torque value of said bolts?

On my initial post. 24Nm

Dankie   :thumleft:

Next question, how serious is the difference in torque between say 20Nm and 28Nm?  Which would be seriously wrong?
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Offline lecap

Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #48 on: March 06, 2014, 12:49:18 pm »
28Nm is 40% more than 20Nm.

20Nm is the standard permissible torque you are allowed to use on an M8x1.25 threaded bolt (or screw) of 8.8 (engineering grade) tensile strength.

The 40% difference between 20Nm and 28Nm might be the difference between intact and stripped or snapped.


Be careful in some cases you have to consider the strength of the material and the geometry of the part a bolt is threaded into too. You might pull an M8x1.25 stud out of a poor quality aluminium cast or out of a shallow thread if you apply the "standard" 20Nm.
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Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #49 on: March 06, 2014, 12:54:23 pm »
I have unfortunately not received the response yet from the gentleman this happened to (which initiated this post), but I can assure everybody this is a completely separate instance from any other caliper issues discussed on this forum or on the BMW forum.

I see this thread has been incorrectly associated with those incidents.

This person's bike was worked on by a BMW dealer.

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Offline BiG DoM

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #50 on: March 06, 2014, 03:37:50 pm »
Just changed KDX200 rear brake pads ... guess what ... noticed even the Japs use fully threaded bolts  :peepwall:
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Offline Garfield

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #51 on: March 06, 2014, 03:43:12 pm »
I have unfortunately not received the response yet from the gentleman this happened to (which initiated this post), but I can assure everybody this is a completely separate instance from any other caliper issues discussed on this forum or on the BMW forum.

I see this thread has been incorrectly associated with those incidents.

This person's bike was worked on by a BMW dealer.

Unfortunately that does not guarantee bolts were torqued to the correct specifications.

Found this out when I checked the torque of the rear wheel bolts after my bike being worked at by a BMW dealer.
 

Offline Heimer

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Re: BMW R1200 GS rear brake Caliper screws design issue. Warning & feedback
« Reply #52 on: March 06, 2014, 03:50:32 pm »
I have unfortunately not received the response yet from the gentleman this happened to (which initiated this post), but I can assure everybody this is a completely separate instance from any other caliper issues discussed on this forum or on the BMW forum.

I see this thread has been incorrectly associated with those incidents.

This person's bike was worked on by a BMW dealer.

Unfortunately that does not guarantee bolts were torqued to the correct specifications.

Found this out when I checked the torque of the rear wheel bolts after my bike being worked at by a BMW dealer.

That is exactly what I suspect happened to this person. - incorrect tightening by cowboy
« Last Edit: March 06, 2014, 03:51:47 pm by Heimer »

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