No, as I understand it, not even the early 2013 LC bikes, but later ones are - contact your dealer who should be able to tell you.
Fork Stanchion Issue... some perspective?
- Thread starter Edmund Kean
- Start date
No, as I understand it, not even the early 2013 LC bikes, but later ones are - contact your dealer who should be able to tell you.
MrMcNamara
Registered user
& you continue to comment on issues that you are not technically qualified to comment on - a dangerous practice indeed. - Stick to electronic issues, if indeed, you have the qualifications & experience to answer. otherwise leave the mechanical issues to those of us who are technically qualified & experienced in, to comment safely
Meanwhile back on the tracks......
I forgot to post up that mine was seen to last month, ended up with the full replacement parts rather than the bolt on sleeve, not entirely sure why. I just phoned up and asked if they had any warranty repair kits in stock.
No visible gap on the forks but the chassis number is on the list so.........
I forgot to post up that mine was seen to last month, ended up with the full replacement parts rather than the bolt on sleeve, not entirely sure why. I just phoned up and asked if they had any warranty repair kits in stock.
No visible gap on the forks but the chassis number is on the list so.........
I am perfectly qualified to comment.
MrMcNamara
Registered user
bollocks! your track record of idiotic / potentially dangerous comments speaks for itself, you are a self opinionated fool
If you have some useful and relevant information about the fork issue then we’d all be pleased to hear it, but if not then please leave to those of us who do.
Troppo
Bemused observer
What discipline is your degree in? Electrical or mechanical?
Will one of the ‘mechanical experts’ on here please calculate the change in angle between the fork sliders and the top triple clamp as the suspension travels through its entire range? An accurate geometric drawing showing the calculation would aid understanding enormously.
Is there anyone on here who can do this?
Is there anyone on here who can do this?
I can't, or rather I'd have to hark back a long way and do a fair bit of revision. Fortunately, there's a bloke at BMW who does this for a living so I'm just gonna have to leave it to him and hope that, after spotting an issue, they got the fix for it right.
fred_jb
Registered user
Sorry I can't do this, and the nearest I've been able to find online is this: http://www.dynamotion.it/eng/dinamoto/8_on-line_papers/Telelever or forks/Telelever_eng.html
However, I think we can conclude two things. Firstly the longer the suspension travel then the bigger the angular movement at the top mounts of the stanchions at extremes of suspension movement, and therefore the more likely it is to exceed the flex available from the rubber bushes in these mounts, and put strain on the weakest point of the stanchions, which is the crimped joints at the top. From this I guess the RT and the GS are less at risk than the GSA, and the lowered versions of the GS and GSA would also be less susceptible than the standard versions.
The other conclusion I would come to is that the so-called "fix" does not actually do anything to solve the root cause of the problem, which is an unavoidable issue of geometry. It just attempts to address the symptoms by stopping the flex from happening at the top of the stanchion which is what causes the crimps to degrade. This need to flex, albeit only at high suspension loadings, has not gone away, so presumably now takes place at the next weakest point. Maybe the stanchions will now bend slightly lower down to provide the extra give needed, and in doing so may cause binding on the sliders and possible extra wear in their bearings.
I think what is really needed is some sort of arrangement, such a spherical bearing in the top mounts, which would provide more freedom of movement than the current rubber bushes, though I guess the danger with this is that it could reduce rigidity in the steering, making it unacceptably sloppy, as steering motion has to be transmitted to the wheel via the stanchions and therefore through these very same top mounts. In this respect I think Telelever is a bit of a compromised design compared to other alternative front ends such as BMW's Duolever and the similar arrangement in the new Honda Goldwing.
fred_jb
Registered user
Thinking about this some more, it seems like bad design for it to even be possible for the stanchions, which are essentially the steering mechanism, to take suspension loads which I thought in this design are supposed to be exclusively handled by the front swing arm and shock. Maybe the evolution in terms of increased maximum suspension travel in these bikes has just exceeded what this design can handle - if you want more travel you can't avoid more angular movement at the top mounts. I had wondered why there is not a hard stop of some sort in the spring and suspension arm movement which would prevent the stanchions from ever reaching the limit of angular deflection which is allowed by the rubber bushes in the top mounts, but maybe this would just be too limiting in terms of allowable suspension travel.
fred_jb - isn’t there a metal spherical bush at the top where the slider joins the top clamp? A rubber bush would be less precise wouldn’t it?
I will have to prise those plastic caps off and have a look.
I will have to prise those plastic caps off and have a look.
fred_jb
Registered user
I found a reference somewhere to the fact that the HP2 had spherical bearings, but I'm pretty sure the current bikes don't. When I looked at this before I'm sure that on the parts diagram it is shown as a bush which looks like it includes both metal and rubber. I'm not sure if there is a rubber layer between the inner and outer tubular sections, but it looks like it from the following video. I used to look at this sort of stuff on Rainbow's very useful parts ordering website, which shows diagrams and part numbers, but can't seem to get to it anymore. Maybe they are revamping their website. However, I found this on a USA website, and I think the part which provides some limited movement is called a joint link, part no 2 in this diagram:
http://parts.bmwmotorcycles.com/a/B...6_5831558/Upper-fork-cross-brace/31_1035.html
The plug which goes into the top of stanchion seems to have a rounded section below the retaining screw/bolt that goes up through the joint link, but I don't think this is a spherical joint. You can see that part here:
http://parts.bmwmotorcycles.com/a/BMW_2017_R1200GS/_51506_5831297/STANCHION/31_1038.html
It seems that the crimped stanchion is made up from three parts, the stanchion, something described as an ISA screw, and an O-ring.
The following picture of this is included in a useful article here: https://www.bennetts.co.uk/bikesoci...7/july/bmw-r1200gs-and-gsa-fork-safety-recall
This is a difficult one to solve without affecting steering precision as I think you need to allow movement within the joint in a wide range of directions dependent on how much steering lock is available. This is because as far as I can imagine it, when the steering is not in the straight ahead position the angular movement of the stanchion under suspension deflection is nevertheless still going to be aligned with the longitudinal axis of the bike, so is effectively requiring a sideways freedom of movement with respect to the top mount fixing.
Fred
fred_jb, from those pictures it looks like the ‘bush’ isn’t really designed to allow any significant repeated movement - I am no mechanical expert 
but I would imagine if there was a continuous changing of the angle as the suspension moved up and down then a spherical bush would be essential - you see the reason for me asking about the angle calculation.
Any clearance in a spherical bush might be felt in the steering, I don’t know how accurately these things can be made.
So the design is still a bit of a mystery to me - I’d love to be able to understand the details because I can’t believe that the BMW Engineers would design something that wasn’t thoroughly understood.
but I would imagine if there was a continuous changing of the angle as the suspension moved up and down then a spherical bush would be essential - you see the reason for me asking about the angle calculation.Any clearance in a spherical bush might be felt in the steering, I don’t know how accurately these things can be made.
So the design is still a bit of a mystery to me - I’d love to be able to understand the details because I can’t believe that the BMW Engineers would design something that wasn’t thoroughly understood.
fred_jb
Registered user
fred_jb, from those pictures it looks like the ‘bush’ isn’t really designed to allow any significant repeated movement - I am no mechanical expert
Any clearance in a spherical bush might be felt in the steering, I don’t know how accurately these things can be made.
So the design is still a bit of a mystery to me - I’d love to be able to understand the details because I can’t believe that the BMW Engineers would design something that wasn’t thoroughly understood.
I don't see why there would be any problem with repeated movement of the inner part of the bush with respect to the outer, so long as the rubber in between is sufficiently durable. You get this sort of design in all sorts of applications, such as suspension components and engine mounts in cars.
Where I think there is a problem is when the angular movement is so extreme that all the give in the rubber part is used up, and the inner metal part is so tilted that it locks against the outer. At that point, as well as potentially damaging the rubber, any further deflection of the suspension cannot be absorbed by the bush, so is now putting a bending load into the whole stanchion and slider assembly, which I presume is the cause of the crimps degrading, though I am sure this will only happen to bikes which regularly experience the maximum possible suspension deflection, perhaps doing jumps and hitting ruts at high speed off-road.
Still - the bike is advertised as capable of that sort of activity, so the BMW designers evidently overlooked this weak point in this design, while using it in bikes with ever more suspension travel. What I can't understand is why the lower arm and shock is not designed to put a hard stop in place to limit movement to less than that which would take the bushes beyond their limits of angular movement, and the designers must be culpable in allowing this excessive movement to ever happen.
On the other hand, maybe it was a deliberate design decision, and they were relying on stanchion flex to allow more suspension travel than the bush design could handle, but perhaps they didn't realise that this flexing would degrade the latest design of crimps, though I would regard relying on stanchion flex as a poor engineering decision, which compromises the separation of steering and suspension loads which this design is supposed to give.
MrMcNamara
Registered user
You are a first class penis, CHANGE YOUR TAG you are an embarrassment to genuine practicing engineers - try the self opinionated Knob - everyone will still know who you are without having to be associated with you
fre_jb, interesting but surely the BMW Engineers would have calculated the extremes of travel and made sure that those bushes weren’t the ‘hard stop’ that caused stress to the crimps? That seems too obvious even to an electronics engineer - are we sure that the shock doesn’t provide the hard stop?
If we assume for a moment that the shock has a hard stop, could there be another cause for the crimps working lose, a large horizontal force to the front wheel, e.g. hitting a high kerb hard, the suspension then doesn’t move upwards but rather the stanchions try to rotate about the lower ball joint and stress the crimps that way?
If we assume for a moment that the shock has a hard stop, could there be another cause for the crimps working lose, a large horizontal force to the front wheel, e.g. hitting a high kerb hard, the suspension then doesn’t move upwards but rather the stanchions try to rotate about the lower ball joint and stress the crimps that way?
fred_jb
Registered user
Well my background is electronics and IT, so I'm not qualified to say anything definitive about this either - this is just speculation on my part, though hopefully logical. It would really need someone to remove the spring and then manually move the suspension to its extremes in order to determine whether the bushes are providing a hard stop or not. However if they are not, and there is still compliance in them at the extremes of suspension deflection, then I don't see how the crimps could be sufficiently loaded to fail, at least not in normal operation.
The other possibility, as you suggest, is abnormal loads, such as hitting kerbs, etc, or maybe just extreme braking loads, but at the end of the day even these should generally get translated into either up or down deflection, or if head on, taken by the lower suspension arm, so I still think such loads should be absorbed without putting bending stresses into what are essentially just a pair of telescopic steering arms. Because it is free to shorten or lengthen as required, I find it hard to see how the stanchion and slider assembly could be stressed other than through excessive angular deflection.
Just been out to the garage to take a look at the front shock on my LC, it does have a hard rubber ‘stop’ fitted - does this limit the travel sufficiently?
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