HPMGuy/R-Dubb triple clamps Group buy - KTM forks on your Airhead!

I got a quote for a recommended-by-someone suspension guy to rebuild my set of WP50's. He said Aus$400-450 for re-springing and revalving (with some test-riding and tuning as part of the process). Around $200 of this price was what he was going to have to pay for springs alone- so your figure of US$150 for springs seems about right (even though our dollar is worth more than yours at the moment, it should be assumed that we would get screwed for parts regardless).
Not sure yet if I will fork out for this quote on the forks or attempt such a thing myself.

On one level I wish I could wrap my head around USD forks on an airhead... For good or worse I just can't. Sure, in their own way the USD's look pretty sexy, but just not the sexy me or my airhead are after
I even got offered a set of 4860's from a 950 adventure for a reasonable price (compared to the cost of wp50 forks and a re-springing)- given the weight of the 950 they might be sprung adequately. Twin discs would be really nice too!
But, even though I have had moments of real doubt and strong leanings towards 4860's, I am just going to stick with the good old conventionals. These forks seem to have mostly good reviews. Hopefully they can be tuned-in to work really well. I am hopeful that a decent single disc and caliper can be made to work well too. I plan on finding some gaitors for the beasts to try overcome the leaky seals syndrome.

I picked up my ktm front wheel and axle the other day,
Tomorrow morning I leave on the R90 for a two day ride up through the high country to pick up my WP50 forks then ride on to stay at a friends place a night before riding back the next day. Great excuse for an adventure!
Brakes will be next and I am not quite decided on what to get yet.
The front end is coming together. Can't wait for these triples.

Looks like 5 now for the WP50's, maybe by the time I am back we will have the numbers!
Cheers,

Boomshaka

See? Those KTM guys aren't all bad.

Just their taste in bikes.

The 50mm guys just about have the quantity to make a run, I will post final pricing including anodizing shortly (waiting for a quote) and also the drawing of the triples for review. When everyone is satisfied, I will order the material and get these in the queue.



As for the 4860 group, it looks like there is some interest beyond the couple who are on the list here, so a run will be likely. From the dimensions above, it looks like the 4860s will use the same top triple as the 43mm forks, with a 54mm bore, so no redesign is necessary. I will rework the lower triple design to accept the 60mm bores, and post the revised design here later this week.

In the meantime, Airhead Wrangler, if you want to pick up a set of the 4860 clamps/stem and send them this way that would be great. I could verify the above dimensions and take a look at what needs to be done to modify the stem. PM me and I'll give you shipping info when you're ready.

Here are the triple clamp drawings for the 50mm Magnums consolidated on one page:

10-4. PM sent.

Guy - is there a way for you to make me a stem and send me the whole thing - triples plus stem, all put together? If not, I'll have to find a KTM stem and send it to you for modifying and installation as well. I want to make this as plug-and-play as possible.

BTW I am in for a set of 4860's, think I already said that though.

dc

Sounding good Guy,

I've tried zooming in on that image and also downloading it and zooming in on it but there doesn't seem to be enough detail to actually read measurements or anything.
Would it be possible for you to email me the high resolution versions of these images- either as one or two images would be fine.
I'll PM you my email address.

Having had a play with my ktm triple clamps and stem within a bmw frame, I have a few questions/issues I want to make sure of/mentally resolve with these clamps.

I won't bother wasting time or space with these queeries until I can have a good look over the final plans.

Thanks,

FYI, I bought a KTM bottom triple and stem on ebay last night and they should be on their way to HPMguy for measurement soon.

Airhead Wrangler is sending over a lower triple/stem assembly. When it arrives, I'll have a better idea of how feasable it is to modify vs. build new stems. I'm open to either....

For some reason the quality of the image degrades when I post it here, I will resolve this issue and re-post the drawings soon.


Got the quote for black anodizing which comes to $18/pair bringing the total for the 50mm magnum triples to $368.

Pricing for the 4860s should be the same + ~$10 for additional material charges needed on the lower triple.

Which just raised the question in my head, what alloy are you using for these? Just curious.

6061-t6511

Glad to see there is interest in making a new run. Very cool!

I happen to have one extra set of the 50mm clamps and forks with a narrow wheel. I might have stem and axle, maybe a rotor. The clamps are from the first run, bare polished aluminum, not anodized. The fork has not been lowered, resprung or revalved. If anyone is thinking about this but does not yet have a fork let me know via PM since I don't mean to hijack this thread.

Also, I'll be happy to answer questions relating to the design if there still are any.

Since some are having trouble reading the images, here are the original plan links. Hole dimensions are for the 43mm USD, which are not being used. On both the upper and lower plans the dashed inner bores are the 50mm holes.

What options are open for bar risers on these triples? Why 6061-T6 and not something stronger like 7075? Why only the 15 degree (or thereabouts) angle of the slit into the leg holes? If it were increased to 30 or so you'd have a larger solid section for the leg to sit in. As is, fore/aft pushing/pulling of the legs loads the threads on the clamp bolts. This loading could be decreased with a larger angle from slit to leg center to X axis. That was tough to put into words. I hope it worked.

Great comments!

All I can say is that these clamps are uber strong. Guy knows much more about the material, but 6061 is cheap, strong and machines beautifuly.

Slit position is all about keeping a clean look that is still very functional. I see your point, but have no concern in this regard.

The bar riser layout matches KTM LC4 spacing and is designed to work with BRP/Scotts stabilizer undermount or any tall, fat bar clamp that uses a pair of 12mm bolts.

Got any pics of what you built? Did you sell your airhead or something? You kinda disappeared from old school.

I've also got a design question.

It is about how you modified the stock KTM stem to fit these clamps.
About the turning it down to fit, and also if any shortening was required.

I recall in a post of yours saying

Was your comment in the above quote 'final' or were their further revisions back to 28mm as shown in the pictures you just posted?
Did you use 30mm stem bores on the upper and/or lower clamps?
I am assuming it was not used on the upper clamp as the bmw bearing has an ID of 28mm and couldn't fit over a stem designed to fit a 30mm bore... I suppose it might seem obvious but I just had to ask,:huh

In short, my question is, what was the final stem bore diameters for upper and lower clamps?
(I am guessing something like 30mm lower, <28mm upper)


I've done some basic measurements on my KTM stem (from a 1999 400SX)
its diameter seems to have a few variations, basically going from fat at the bottom where it presses into the lower clamp, and skinny at the top where it is clamped in the upper clamp.
I don't have an exact measurement (which I should get) but the KTM stem is longer than a stock bmw one.

Sorry for the ramble below-

my rough-ish measurements, from bottom to top of stem where this:

diameter 1 where the stem is pressed into the lower triple = 32mm
diameter 2, interference fit for lower bearing = 29mm
diameter 3, middle section that is less than diameter 2 so lower bearing slides easily into position= 28.5mm
diameter 4, interference fit for upper bearing (same as diameter 2) = 29mm
Diameter 5, interference fit for upper triple clamp = 28mm

Has anyone else measured their KTM stem?
From WP50 forks are they all the same? Does this sound about right?

If these Triples manage to use the standard KTM length of the stem, and if the upper stem bore is 28mm (or smaller)(and the lower stem bore anything less than 32mm) I see no problem using this stem by getting it turned to fit.

Sorry for the long winded ramble,
I'm just trying to get his all straight in my head.

Cheers,



P.S. R-Dubb, Excellent to have you back answering questions!
It would be great to hear your story, and also any feedback you may have received from all the people who have used these clamps and the 50mm extreme forks.
I am particularly interested in how some may have re-sprung and re-valved these forks, and other more general set-up procedures (different oil weights, etc) for their use on our beemer pigs

I dropped out of ADVrider altogether for a few years. Got unemployed, started a new biz and had no time or money for motorcycles. Still no money but have a little more time...

Anyhow, I abandoned the airhead project midstream. I've still got enough stuff to build two, maybe three bikes. I've got one rolling frame. It's been fully reinforced, has an extended swing arm (+100mm), and a 50mm fork with fat bars and a submount. No motor, no nothing yet. I'll get back to it, maybe sooner than later.

My really sweet R100, McPeeDee, crashed and was abandoned on the way to Bolivia. Still crying over losing that one.

The stem from an old LC4 won't work. The ones to use are from the RFS models. I'll dig up a part number for that also. Ill also measure the bore on the finished clamps. Pretty sure it did get changed to 30mm. The correct KTM stem sells for about $80 and can be potentially turned down on a drill press with a file if a lathe is not handy. Somewhere I have a sketch for that too, but it is super simple to do. The bore we ended up with was about a thousanth tight, but with a big press the stems went in. It is the BMW bearings that require a close shave to the shaft.

RFS? I'm not up on my KTM acronyms.