An Unholy Union III: WP 4860 USD Forks on an Airhead

[hpnbobo]

Originally Posted by igormortis

FYI, here are the bits I used to make the GS wheel fit the KTM forks with HPM/R-dubb clamps.



From left to right:

- Monolever road bike axle. 30mm, 25mm (mine was from an ’85 R80)

- standard axle spacer. 11mm
- standard axle spacer, machined down to approx 17mm (spacers and axle came from the same road Mono bike)

- steel sleeve, 0.5mm thick to bring the BMW axle up to the KTM’s 26mm. Split to allow tightening. Approx 58mm in length, with about a 4mm “hat” to keep it located. This is against the inside of the axle clamp and acts as an additional spacer.

- steel shim. This is what the hat part of the sleeve tightens against when the axle is pulled into position by the end bolt.

Not pictured: Axle end shim and bolt. These are standard items from the above Monolever bike.

Thanks for sharing your great project!!
Mine is here: http://www.bmwgsclub.nl/forum/viewtopic.php?t=50020

[hpnbobo]

First new bearings:

The SWT special parts and wp 4860

stronger springs

Final

[hpnbobo]

Originally Posted by igormortis

FYI, here are the bits I used to make the GS wheel fit the KTM forks with HPM/R-dubb clamps.



From left to right:

- Monolever road bike axle. 30mm, 25mm (mine was from an ’85 R80)

- standard axle spacer. 11mm
- standard axle spacer, machined down to approx 17mm (spacers and axle came from the same road Mono bike)

- steel sleeve, 0.5mm thick to bring the BMW axle up to the KTM’s 26mm. Split to allow tightening. Approx 58mm in length, with about a 4mm “hat” to keep it located. This is against the inside of the axle clamp and acts as an additional spacer.

- steel shim. This is what the hat part of the sleeve tightens against when the axle is pulled into position by the end bolt.

Not pictured: Axle end shim and bolt. These are standard items from the above Monolever bike.

It works well!!

ride like new!!

[hpnbobo]

Husaberg 6 piston brake cal.
Homemade disk adapter
disk 310mm braking made for a ktm supermoto
ufo fork protector
SWT sports Y yokes
16mm magura bmw brake piston Ex R100RS
5Nmm springs from s tech

The first ride was great!! the disk gets a blue color.

[Airhead Wrangler]

I finally assembled my front end onto my bike a few days ago and everything fit up well. The steering head bearings were a tight fit on the stem, but nothing that some freezing and heating couldn't cure. Removing them will be a PITA some day though. The only problem I'm seeing now is some EPIC stiction. I've gone through the recommended method of wheel installation to minimize it, but was wondering what other setup tips anyone might have for installation and alignment of 4860s. This is just a pair of ebay forks that I haven't opened up yet, so it's entirely possible that the internals are hosed and in need of a rebuild, but I'd just like to eliminate all other possibilities first.

[Prutser]

Those forks do have a lot of stiction. Most of the time its caused by the seals. And shimming the bushing helps a lot.
But thats a lot of work. And give the bike some more sag to give the inner en outer tubes more overlap.
Don't tighten the bottom triple bolts to much.

The SKF seals are an enormous difference. But they are expensive compared to others.
For your fork they have 2 types. One of them is a set with tighter dust seals.(for wet conditions) and give more stiction again.

[hpnbobo]

most important are the spings not to hard or soft, for the beemer you need the hardest. 5 N/mm

if its not good already try spacers. my best setting is 7cm in. thus 23cm is left over.

fill chambers with new sae5 oil

take a ride with combustion en rebound with the max. setting.

if he still drives like a jojo its time to change shims.

[hardwaregrrl]

Originally Posted by Airhead Wrangler

I finally assembled my front end onto my bike a few days ago and everything fit up well. The steering head bearings were a tight fit on the stem, but nothing that some freezing and heating couldn't cure. Removing them will be a PITA some day though. [/IMG]

Looks good!!!! I had to have my stem buffed and sanded down just a tad in order to get the bearings to fully seat.....keep that in mind when setting preload, but I guess you won't know until you ride that beast!

[ontic]

Originally Posted by Airhead Wrangler

The only problem I'm seeing now is some EPIC stiction… This is just a pair of ebay forks that I haven't opened up yet, so it's entirely possible that the internals are hosed and in need of a rebuild, but I'd just like to eliminate all other possibilities first.

Looking good. I had epic stiction too when I put my WP50's on. Like someone kindly told me, don't stress yourself about it or wheel alignment or problem shooting until you open them up.
This was mine- and that filth was even more packed between the oil seals and the tubes.


And yeah, I think you followed our bearing and stem issues in the WP50 thread? Preload is important, and the KTM instructions how to get there kinda irrelevant (IMO), so is using at the least the correct thickness bearing covers- I got into a bit of trouble not doing that. I think that ktm stem and short alu blind nut are running pretty close to their design limits in putting the right torque on our bmw bearings.
If you have an older longer thread alu blind nut available, that felt a lot better. Alternatively if you have a welder handy and a spare swing arm bolt and nut then you could make a nice steel one which feels even better again. There really is a huge difference in how it feels to torque up that short thread blind nut compared to either of the longer thread ones.
I was going to make a few to send over for Solo and Jenna but my welder is still broken

Long thread nut and washer left, then the newer short thread style, then steel DIY and what the steel one started like.

[R-dubb]

Originally Posted by AntonLargiader

OK. Dunno if the 4354 has a different axle offset (I sort of doubt it's significant) but the last diagrams I see in his design thread show 35mm offset and the clamps are made to 38mm, so clearly there was some more work done.

Anyway, you sort of confirm my suspicion that this clamp may not be optimized for my wants. I'll just have to do a bunch of figuring and see where the trail ends up on an R100GS.

Anton, if you are still paying attention this may help your understanding.

I finally got around to reading this thread and though I would chime in on the subject of offset. It's all fairly controversial, and probably less significant in the performance than we all think it is. After all, the airhead has tremendous rake by modern standards. When I saw other airhead fork adaptations, including HPN, were using clamps with very small offsets, this just didn't make sense, unless one was willing to steepen the head angle in order to use them.

The design intent was to produce a clamp that would work with standard rake. I also assumed that if the front were raised for more travel, the rear would be raised an equal amount. Now having said that, I can't remember exactly how I ended up with 38mm of offset. There was plenty of discussion in the design thread at the time. Ultimately, I believe the offset was bumped to 38 in an effort to sharpen steering given that a better suspension doesn't need quite as much trail to behave well. The stock offset numbers are easy to come by also.

According to my measurements the WP4357 and the 4860 both have 36mm at the axle. So, the total is offset is 74.

[naginalf]

Does 4860 mean 48mm top diameter, 60mm bottom? Just wondering because I'm considering getting a set of HPMguy triples, and it looks like he's doing a run of both 50s and 4860s. I prefer the 50s and have a line on some , however the 4860s are much more common and modern. So my crazy brain is thinking, why not get a 4860 bottom clamp and a 50 top clamp, machine up a 5mm aluminum collar for the 50s to fit the bottom clamp, and if I ever get a set of 4860s, I can simply use a 1mm shim on the top clamp. Feel free to tell me I'm a crazy idiot , but at least assuage my ignorance in the matter .

[LukasM]

Originally Posted by naginalf

Does 4860 mean 48mm top diameter, 60mm bottom? Just wondering because I'm considering getting a set of HPMguy triples, and it looks like he's doing a run of both 50s and 4860s. I prefer the 50s and have a line on some , however the 4860s are much more common and modern. So my crazy brain is thinking, why not get a 4860 bottom clamp and a 50 top clamp, machine up a 5mm aluminum collar for the 50s to fit the bottom clamp, and if I ever get a set of 4860s, I can simply use a 1mm shim on the top clamp. Feel free to tell me I'm a crazy idiot , but at least assuage my ignorance in the matter .

That's not how it works.

You need to differentiate between upside down and conventional forks:

50mm Extremes are conventional, so both upper and lower triple clamps clamp to the 50mm slider/stanchion (the chrome part on top).

The 4860 are USDs that use a 48mm slider (the chrome part on the bottom). Their upper tube/stanchion measures 60mm where the bottom triple clamp clamps to and 54mm on top.

Clear as mud?

[naginalf]

Originally Posted by LukasM

That's not how it works.

You need to differentiate between upside down and conventional forks:

50mm Extremes are conventional, so both upper and lower triple clamps clamp to the 50mm slider/stanchion (the chrome part on top).

The 4860 are USDs that use a 48mm slider (the chrome part on the bottom). Their upper tube/stanchion measures 60mm where the bottom triple clamp clamps to and 54mm on top.

Clear as mud?

Thanks for the quick reply. I understood the USD vs conventional thing (oh yeah, duh, I get where the confusion is there, 48mm stantion, 60mm tube), but a clamp is a clamp, right, just gotta hold it tight? Anyway, doesn't matter for those measurements, my idea is bunk if the top is 54. I wouldn't mind using a 5mm collar, but a 2mm one is just too thin for front fork stress, and I'd like to have at least one of the clamps directly on the fork tubes. Sorry, just trying to get 2 for one but thanks for setting me straight.

Although, if you'll humor me for one more question, how much would you trust a 5mm bottom AND a 2mm top, machined aluminum collar (with a compression gap of course) to hold a set of 50mm conventionals in set of 4860 triples?

[LukasM]

1. I am not a mechanical engineer
2. The smart solution would be just to buy the correctly engineered clamps for your application, and to sell the ones you don't need if you change them later, then it won't cost you all that much.

That being said, if you really wanted to use the same clamps in both applications, I think a shim with 2mm wall thickness would not be a problem since they are just clamped in between.

What I would definitely do however is to machine them with a lip on top and bottom so that there is no risk of them slipping out of the clamps. That, and roughing up the surface on the inside so that they don't slip on the chrome sliders of the conventional forks. Doesn't have to be anything crazy, just not a smoothly machined finish.

[Box'a'bits]

I you look on the Boxer Supplies site, you'll see some triple clamps for sale, as well as some inserts to accomodate different fork tube sizes. So the concept is good & already out there.