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Old 05-01-2012, 01:23 AM   #556
ontic
 
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Quote:
Originally Posted by SOLO LOBO View Post
That said, I wouldn't be suprised if the pre-load stays where it is now. Fingers crossed at least.
Assuming the stem pinch bolts are tight, hopefully it stays put.
Since reducing the interference on my stem I think I'll be leaving my blind nut torqued up! When it comes time for the 'final' time to put it back together, I might even dribble a little loctite retaining stuff down the top bearing/stem before torquing it up.
Do you have a beam type torque wrench? 35-40 ft-lbs is quite a lot to achieve on my Bahcho 1/2" shifter without extending the handle with a breaker bar- I really only mentally noted this last it as it is much easier to reach on my big long beam torque wrench.
When I put my front end back together, maybe tonight if I don't get home too late, I'll try to get a good measurement of what my 'typical bmw preload' gets to.


Quote:
Originally Posted by hardwaregrrl View Post
Sorry Hans!! As you were posting, I was disassembling.



No way to really measure it. My needle was also apart and was visabley bent at the tip. But you'd have to roll it to see....
No problems Jenna. So, another rebound needle separated from its adjuster- were both needles (the bent and the unbent) like that?
Solo, did you ever take your rebound needle out, and if so, was it whole?

Jenna, I glued mine in all the way like yours is pictured- it does seem like the logical way to do it don't you think?

Quote:
Well, I just did the rebound side tonight. And I made a fucking mess!!!
Tell me about it, I've emptied fork legs three times now and most of it ended up on the floor.

what I can't believe is the parallel evolution here. I make a set of on-the-fly adjusters and lament my innability to knurl them. You find their knurled twins on the other side of the world. I really want to see how they attached the knobs to the adjusters.








Quote:
Originally Posted by redboots View Post
Ok, not to muddy the waters but hopefully as a help, this is the page from my 250excf manual.
As you can see, it says to tighten the stem nut to 10nm and also to loctite the stem pinch bolt.


Happy spannering.
The sun is shining here this morning after 14 straight days of rain so I'm out for a road test on mine ... too wet for any tracks on this tank though

Cheers,
John
Thanks for posting that John. 7.4 ft-lb aint much, but since getting my top bearing to slide down it might be about right.
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Old 05-01-2012, 04:50 AM   #557
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Hey Hans, the "new" rebound needle was not seperated, just the old one. I'll take a pic of the adjuster knobs on may way out for a run.

Bummer is my knobs are pretty big and inhibit the bleeder screw, so I probably wont be able to put a bleed valve in. Did you ever find one to fit?
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Old 05-01-2012, 05:31 AM   #558
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Hey Jenna, I am just previewing a big post I am about to unleash after this one

Yeah, I did find speed bleeders, I've just bought some and they are on the way to Solo's to meet up with a few other bits for the 'next shipment'.
Maybe you could turn your adjuster knobs down a bit more so you can fit speed bleeders?

I went with the System Tech Racing bleeders- they are a bit pricey but they seem like they are well designed and the last thing I want is problems. They are also very small and compact.
http://www.systemtechracing.com/Articles.asp?ID=143

slavens' has a good page for them, worth reading,
http://slavensracing.com/products/kt...-bleed-buttons


Basically after measurements and photos it was confirmed by STR that we need 5mm ones as used on "Honda, Yamaha, Kawasaki,Suzuki, Husqvarna w/KYB or Showa"

at least my forks with these bleeder screws do



next post coming up
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Old 05-01-2012, 05:39 AM   #559
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dug a bit deeper in the rebound fork,

eewww



aside from a heap of muddy rusty crud around the dust and oil seals, things didn't look too bad.
Cleaned it all out and put it back together, including installing the glued in rebound needle and filling it up with ATF to match the other side.
Of course, no seal driver...
KTM triple clamp to the rescue!



The first move was to just use the triple clamp- the lip on the bottom easily drove the oil seal below the rim of the slider, then I destroyed a spray (rattle) can lid and with that between the triple clamp and placed on the strong bit of the oil seal, that drove it the rest of the way home.

With some garage bouncing up and down it looks like the worst of my stiction is gone- post pull or push with the front brake on the forks return to the same spot now It is still a bit grabby but then so are most other forks.
Now all I have to do is drain the compression fork... again... and give it this level of a clean. The oil was a lot better in them and there was no rust, but I didn't clean under the dust or oil seals- most likely they are similarly clogged like the rebound fork... but I've had enough oil for tonight.

I also re-checked the torque on the blind nut (I'm starting to appreciate the name of that thing). Solo was right on the money- 35-40 ft-lbs is the point where I can begin to feel the steering tighten towards typical bmw preload. I am not even sure if I am there yet but I don't want to take it any further. That is a lot of torque on this dicky little aluminium nut.
Is there something we are missing here?
In my mind there is no way that 7.4 ft-lb of torque and a love tap on the triples is going to give the bearings enough preload









So, after a little headscraching, I have a theory to float. Someone who understands this stuff needs to check my thought train.

The KTM and BMW headstock bearings are different. They are both tapered roller bearings of course, and designed to carry axial and radial loads, however they have different contact angles.
Put them side by side and you will see- the rollers on the BMW bearings are 'steeper', the KTMs 'smaller'.

pic from this google book



SKF have a nice basic write up about this stuff and this where the images below are from




the higher figure a (or the more like a BMW bearing) the higher the ability to deal with axial loads, the lower figure a (the more like a KTM bearing) the higher the ability to deal with radial loads.


Of course the bearings aren't hugely different- obviously they will both deal with radial and axial loads. What is different though is what preload is required for tapered roller bearings with different contact angles.

I've dug through pages of literature trying to find something of authority that says simply what my instinctual understanding tells me, but I haven't found it yet.
Basically it seems very obvious to my mind that steeper the contact angle (the more like a BMW bearing) then the more preload that bearing will need/want (just imagine an extremely steep angle bearing and how much more preload it would need- or a very small angle bearing and how little preload would be required).

So, in my mind, what we have here is a KTM style triple clamp designed for a smaller angle tapered roller bearing that requires a lighter preload and lesser torque on the blind nut than the BMW style bearings we have put in them- what that means to me is that the torque spec of listed in the KTM literature is irrelevant to preloading our bearings correctly. What that also means to me is that this aluminium blind nut, with it's very short thread into the aluminium stem, may not really be up to the task of correctly preloading our bmw bearings.
How to deal with this I am not sure.

What do people think of this argument?
I for one am going to stick the older longer thread nut I have into my stem. With more thread I feel confident I can torque it up a bit more (and last night proved to myself that I can actually tighten the steering with that nut).


Currently I've done like Solo and after torquing up to around 40ft-lb tightened the pinch bolts down and then slightly loosened off the blind nut to around 20 ft-lb.
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ontic screwed with this post 05-01-2012 at 05:45 AM
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Old 05-01-2012, 05:59 AM   #560
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Old 05-01-2012, 09:50 AM   #561
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Quote:
Originally Posted by ontic View Post
What do people think of this argument?
Don't like it.
Been reading my BMW manuals and for the early type like that now fitted to my bike, it describes the procedure of removing all free play. No more. The top nut is then torqued down to large figure to hold it all together. Not to exert a load.
The later models have a different adjuster that carries the top bearing. This is just a large "saucer" with a knurled edge so you can adjust it by hand.

I think the idea of the different types being able to accept more or less "preload" is not valid and refers to the loads exerted after fitting (correctly).

I have just been for a ride on mine and they were a little on the tight side... it felt like there was a steering damper on there... remember the old screw down ones people used to fit to Triumphs... (Nortons never needed them)
Its a little better after 100 miles but I think I will back it off a CH. Try the KTM way. Get a helper to slowly turn the blind nut while you hold the forks and rock them fore and aft to feel for movement. Stop when there is none and lock it all off.

Writing that may have just put the light on!
The blind nut. IS IT THE RIGHT ONE? There should not be a washer used.
Looking at rdubs(?) drawing of the top clamp, its the same as the KTM system. The pinch-bolt not only pinches to the stem, but also the blind nut. This is what locks it all together... Not torque... or am I talking bollox


Cheers,
John
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Old 05-01-2012, 10:14 AM   #562
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First road test and I like it
I put a wire-tie on the stanchion before riding it and after a few ham fisted applications of the brake, I managed to push it up by 153mm, leaving me 54mm "spare". I may drop the forks down a bit more as that seems a lot



The bike tracks really well and soaks up rough roads a treat.
I have some problems with the lack of steering lock. I will have to grind some of the cockpit away to clear the top of the legs unless I can slide enough through the top triple.

Looks good as well... impo





Also need to lengthen the side stand a bit and I think I may have a front wheel bearing on the way out...


Cheers,
John
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redboots screwed with this post 05-01-2012 at 01:08 PM
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Old 05-01-2012, 03:51 PM   #563
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Looks nice, John!!! What will you do for gaiters??
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Old 05-02-2012, 12:44 AM   #564
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Originally Posted by hardwaregrrl View Post
Looks nice,
Thanks very much I wanted to keep it looking a bit like it should. Thats why I didn't go for USD forks.

Quote:
Originally Posted by hardwaregrrl View Post
What will you do for gaiters??
Thinking about something like these: http://www.dirtskins.com/
I have one on the rear shock and they make them to the sizes you want.

Cheers,
John
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Old 05-02-2012, 04:39 AM   #565
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Looking great John, congrats
Looks like a lovely spring day too- it was raining and cold and miserable today (and most days) here.

now back to the bearing stuff,

Quote:
Originally Posted by redboots View Post
Don't like it.
Been reading my BMW manuals and for the early type like that now fitted to my bike, it describes the procedure of removing all free play. No more. The top nut is then torqued down to large figure to hold it all together. Not to exert a load.
Technically the top nut does actually exert a small load, because when you torque it up properly it pushes the crown nut down to the other side of the threads- that is one of the reasons the adjustment on that older style bmw stem (like on my R90) is a bit fiddly- if you set it 'right' with the crown nut, then torque up the top nut, it gets too tight. The later (GS etc) style system set about 'fixing' this issue. I think Antons site goes into this, but that is beside the point.
I also believe that technically there is meant to be some preload, wether or not the bmw manuals decide to call it that. Not a great deal but a little bit- it does go beyond removing free play- and comes down to setting the 'fall away' (the point where the bars will fall once turned)- the fall away point is determined by the drag on the bearings and the drag is produced by preload... and for me, what is important here is that the steeper the contact angle of the bearing, the more torque will be required to remove play and get to the correct preload that will give you this correct fall away.
That was a mouthful.

Quote:
[/I]I think the idea of the different types being able to accept more or less "preload" is not valid and refers to the loads exerted after fitting (correctly).
My argument (based for the moment on limited understanding and gut feeling) is that in order to fit tapered roller bearings into steering heads 'properly' they need to be preloaded correctly and that the steeper the contact angle on the bearing, the more torque and/or preload is required.
Try to think about it in terms of an extremely steep angle vs an extremely small angle tapered roller bearing.



I know how to set the right preload on an airhead (my R90)- that is I have had the experience of both too loose and too tight bearings and I now have a way (eliminating play, testing the drag on the bars and setting the fall away point, and of course feeling how the bike rides after all this) of setting this preload in the middle- which to me is right. There is no way that I could get the torque required on the crown nut by twisting it by hand- it taks a good deal of leverage on the crown nut with the special tool to get to this point.
What I find it very hard to do is to reach this same point on my G/S with these same bearings but a different stem and tightneing method. I can get there, but like I said, it comes from torquing up that blind nut to 35-40 ft'lb, not 7.4 ft-lb, not even close.



Quote:
I have just been for a ride on mine and they were a little on the tight side... it felt like there was a steering damper on there...
see, that is just my point It is virtually impossible for me to (currently) get to that too tight point that you just easily and accidently got too.
For me, I think hitting 40ft-lb on that aluminium nut just started to feel like it was heading into the too tight zone, and this was well and trully into the torque zone that felt too tight for the aluminium blind nut (not the bearings)



Quote:
Its a little better after 100 miles but I think I will back it off a CH. Try the KTM way. Get a helper to slowly turn the blind nut while you hold the forks and rock them fore and aft to feel for movement. Stop when there is none and lock it all off
Call me dubious but I've already sanded one step out of my stem from (I can only assume) the steering head having too much play and hitting speed bumps for a couple of hours hammering them back and forward. Considering we are using bmw bearings in the steering head, I am more inclined to use the tried and tested method of removing play, and setting the (very slight) drag and the 'correct' fall away point of the bars. The KTM instructions don't get me there.

Quote:
Writing that may have just put the light on!
The blind nut. IS IT THE RIGHT ONE? There should not be a washer used.
Looking at rdubs(?) drawing of the top clamp, its the same as the KTM system. The pinch-bolt not only pinches to the stem, but also the blind nut. This is what locks it all together... Not torque... or am I talking bollox
here are two blind nuts- the one of the left is the new ones that have a washer built in- the thread, the washer and the nut head are all one piece of metal. Good observations! You might be right in that the triple might pinch the washer as well as the stem- at 7.4 ft-lb of torque on the nut I suppose that is a good thing as loosening out might be possible?
The other one with more thread is an older one from my ktm triples that came with the forks, it has a seperate washer which won't do a thing if pinched, however it has more thread and felt much better being torqued up to 40 ft-lb than the other one did...



I don't know, this might all be a storm in a teacup. If my idea of different contact angle bearings needing different torque to reach no play and the right preload (for steering head application) is correct, hopefully we have enough redundency built into the ktm stem/nut system to get to where we need to be on the bmw bearings (without stripping the stem/blind nut threads in the process).

What I can only repeat is that 7.4ft-lb torque on the blind nut, no matter how much you pound the triple clamps and shake the forks, TO ME (and I might be doing something wrong), does not feel anywhere near enough preload on the bearings, and it gives a fall away point that is pretty much a fraction of a degree off from center (ie, falling too soon in my experience).


Sorry for the long tedious posts peoples. Hopefully it is of some interest or use, even if it is just for an engineer type to step in and completely discredit everything I am thinking. I'd like to get this right,

Cheers,
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ontic screwed with this post 05-02-2012 at 05:27 AM
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Old 05-02-2012, 06:33 AM   #566
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Sorry for the long tedious posts peoples. Hopefully it is of some interest or use, even if it is just for an engineer type to step in and completely discredit everything I am thinking. I'd like to get this right
Its ok. Sometimes just writing it down will clarify things... or not

John
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Old 05-02-2012, 11:54 AM   #567
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So....$120 bucks later!!!!! My stem was too large for the inner race to slide down. It took him quite a while to remove the lower bearing race. Stem and bottom clamp are in the freezer and bearings are greased and under a low watt bulb. I should be back on the road in a few hours!!! Well, maybe by 9pm est.
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Old 05-02-2012, 02:37 PM   #568
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So....$120 bucks later!!!!! My stem was too large for the inner race to slide down. It took him quite a while to remove the lower bearing race. Stem and bottom clamp are in the freezer and bearings are greased and under a low watt bulb. I should be back on the road in a few hours!!! Well, maybe by 9pm est.
Ouch. What, does he turn them down with gold chisels and polish them with diamond powder, that he grinds up himself, from big diamonds?

I'm baffled how you got your bearings on in the first place!
Good luck this time, I hope it goes well.
Maybe we could talk about fall away angles- mine (preloaded at 35-40ft/lb) falls at a very slight turn of the bars- like the very front of the tyre moving 5cm or less to one side (which is very little at the bars).
Off to work, hoping for good news when I get back,
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Old 05-02-2012, 03:35 PM   #569
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Ouch. What, does he turn them down with gold chisels and polish them with diamond powder, that he grinds up himself, from big diamonds?

I'm baffled how you got your bearings on in the first place!
Good luck this time, I hope it goes well.
Maybe we could talk about fall away angles- mine (preloaded at 35-40ft/lb) falls at a very slight turn of the bars- like the very front of the tyre moving 5cm or less to one side (which is very little at the bars).
Off to work, hoping for good news when I get back,
Yeah, I think I wanna be a machinist when I grow up! He also repaired the threads in the stem and on my 2 blind nuts, and he removed the inner race of the bottom bearing off the stem. Have a good day at work!
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Old 05-02-2012, 03:44 PM   #570
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Hey, what are you guys using for torque value on the pinch in the lower, upper clamp and at the stem.??
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