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

[HPMGuy]

what alloy are you using for these? Just curious.

6061-t6511

[R-dubb]

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.

[R-dubb]

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.

[Airhead Wrangler]

Originally Posted by R-dubb

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

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.

[R-dubb]

Originally Posted by Airhead Wrangler

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.

[Airhead Wrangler]

Originally Posted by R-dubb

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.

[ontic]

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

Originally Posted by R-dubb

The stem bore will be 30mm (rather than the 28mm which is shown) and will take a KTM stem press fit.
A KTM stem and nut will fit if turned (0.5mm+/-) to accept BMW head bearings.

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,

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

[R-dubb]

Originally Posted by Airhead Wrangler

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

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.

[R-dubb]

Originally Posted by ontic

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

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)

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.

[Airhead Wrangler]

Originally Posted by R-dubb

The stem from an old LC4 won't work. The ones to use are from the RFS models.

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

[SOLO LOBO]

Originally Posted by R-dubb

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.

Hi R-Dubb, good to see you 'round again...

Just to be clear here, are you saying the 640 WP 50mm triple stem won't work with HPMGuy's triples?

[R-dubb]

Originally Posted by Airhead Wrangler

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

Jeez, you guys expect me to give up all my secrets

Give me a day or so. Will post all the info you need.

[SOLO LOBO]

Originally Posted by R-dubb

Jeez, you guys expect me to give up all my secrets

Give me a day or so. Will post all the info you need.

Thanks!

At least three of us have stems that are from the stock WP Extreme triple clamps (me, ontic and walking bear)... need to know if these stems would work if the ID of the triple could be changed and if HPMGuy could even change that ID at this point.

[R-dubb]

Originally Posted by SOLO LOBO

Thanks!

At least three of us have stems that are from the stock WP Extreme triple clamps (me, ontic and walking bear)... need to know if these stems would work if the ID of the triple could be changed and if HPMGuy could even change that ID at this point.

Good news!

It looks like the KTM stems, until very recently, are the same part number (which is the one needed). LC4's & RFS from the WP 50mm Extreme days throught the WP USP 43 and the 48's all use the same 30 x 244mm stem.

50101033100 FORK TUBE L=244 '91 80.49

You'll also need the cap.

54801036000 STEER.HEAD SCREW M20X1,5 WS=27 11.49

Just to refresh, the idea here was to use BMW bearings because they fit the frame. Then we designed the triple clamps to make a 248 +/- mm sandwich with the 244mm stem. This leaves around 4mm for preload and stack tolerance. The stem modification is only required because the BMW bearings are a little smaller in the waste line.

Below is the drawing. Guy needs to bore the lower clamps for a 30mm interferance fit like he did last time. They were a little tight but worked with a heavy press and some heat. The vertical transitions can move around to match the KTM stem as it is not critical where the tapers start and stop. They just need to catch the bearings. The bearing tapers shown on the drawing are too big in diameter. I'm a little dumb and 28.10mm is way too large to slide a 28mm bearing over even with heat. Needs to be more like 28.03mm. Not a big deal, but if you heat the bearing and try to stretch it on there it will never come off!!...DAMHIK. So that should also be adjusted accordingly.

I would not be afraid to make these modifications to the stem using a drill press and a file. Worst that can happen is you mess it up and need to buy a new stem, assuming the measurements are taken somewhat seriously. My recollection is that KTM uses 29mm ID steering bearings, meaning that to take off half a milimeter all the way around is not a big deal. Someone else will be able to measure these and report back. My machinist did about six of them for me last time. Took no time at all. I like the KTM stems because they are hollow, strong, and match up perfectly.

Thats about it for now on the stem front.

[R-dubb]

The bosses on the top clamp were designed to match up with a standard BRP submount.

The model I ordered from them on the phone (won't come up on web site) is:

model number: SMO-9018P3 - 90mm spread; 18mm offset.

It looks like this (very nice!!):



Works with Fat bars and a Scotts Submount Stabilizer



Any generic 12mm bolt, two piece, bar clamp set will also work.