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Old 01-29-2011, 10:27 AM   #1
Some Dude OP
what attitude problem???
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Joined: Dec 2003
Location: Woodstock, GA
Oddometer: 4,758
BMW HP2 WP48 Fork conversion kit

Okay, so I've been working on this project after inspiration from Ebrew over a year and a half ago and have just now got it to a production level "kit".

From the beginning,.............I have had wet dreams about the HP2 Enduro from the first teaser video BMW had put out prior to it's release. As luck would have it I managed to have the first dealer delivered HP2 in the USA and the love affair was consumated.

Through the few years of ownership now I have used the bike in many forms and fashions with it spending most of it's time with the SM wheel kit. I had used the bike in a couple of Rally events and did very well with it in the road events. However I constantly had to ride around the level of suspension performance. As soon as there was a good progressive stiffer front fork spring I installed it and then played with oil viscocity and level to attempt old fashion fork tuning. That helped but still left alot to be desired for on road and aggressive offroad performance. I actually like the air shock for dual sporting and touring as it's the most comfy and gets the best traction out of any rear shock I've tried offroad, but it has very distinct limitations when pushed and particularly lack of rebound adjustment on the road when stabbing at the front brake in traffic or on a closed course. At that point I upgraded to an Ohlins rear shock since we are able to fully service and tune them over the Wilbers. The Ohlins rear shock definitely helped stabilize the bike in all conditions and improved the on road performance drastically. I gave up a little traction on off-road technical sections, but gained rebound control which made for a more stable chassis and result from my inputs.

At this point it I started to look back at the front forks. I had ridden 2 different HP2's with OEM forks that had been massaged by well known tuners, but they still weren't meeting my expectations. Some would say (such as Wunderlich) that the OEM triple clamps were to blame with too much flex, others say the front fork angle is suspect and then many would say the 45mm non-Shiver Marzocchi suspension is the biggest issue. Well I can say I've seen 45mm Zokes to very well on G450X's after some tuning, but they are a much more conventional designed valving configuration.

In come's the option of a fork swap. I installed WP48's on my G450X over a year 1/2 ago and loved what it did for my bike (even BMW races the G450X with 48mm WP's or 52mm Zokes on the Rally bikes). I spoke with Ebrew a few times and it appeared his Machinist wasn't interested in reproducing 1 or even 4 more of the lower triple clamps of the 1 he had made prior. Top that with good design but could have been better and we moved on to a different machinist. I was in the process of rebuilding my bike after a couple of mishaps fending off Jonah Street (not too succesfully I might add and that turd was on a Husa 570 instead of a big bike ). The fork clamps were already off and I sent them out to a machinist in Oklahoma,.........well 5 months later I finally had 4 clamps (really long story, but kind of relates to the whole US Highland fiasco), I then started figuring out the parts necessary to install some WP48's. I did my research and found that the KTM 950 SE along with maybe 2004 KTM 950 Adventue S models use the longest travel and most overlapped fork WP makes. This also makes that fork the longest overall, however the 950SE has a fork to fork width the same as their single cylinder dirt bikes where the BMW HP2 E has a width identical to the KTM 950SM's (210mm center to center). That means I couldn't use OEM KTM 950SE axle or wheel and needed to adapt the OEM BMW wheels to the WP forks, which is what I wanted to begin with as I have more BMW HP2 wheel combinations then most could imagine.

Back to the WP fork options,.... A KTM 950SE fork is approximately 960mm from top cap to top of axle. The KTM WP fork found on all current generation single cylinder bikes is approximately 920mm while the BMW HP2 E Zokes are approximately 900mm. Fortunately all of the KTM WP48mm forks with single brake rotor have the same feet for axle diameter and brake hardware. The right side of the BMW front axle is the same diameter as the right fork leg of the WP48's and the left fork leg foot is 1mm larger then the BMW's axle. We took a piece of stainless and carefully machined it to make a shim that is approximately .5mm thick (actually a tad less) and with a slit so that the axle clamp can do it's job. Once I had the axle and wheel installed in the new forks, it was time to center the wheel. I had a couple of wheels so we tried them all and measured the average to get a new wheel spacer for the brake rotor side of the wheel that will center the wheel. Fortunately this did not offset the axle so much that we needed to make a new axle, however with the bigger diameter of the WP48's left axle clamp/foot and the 1-2 thread we gave up re-centering the wheel it was deemed a good idea to make up a new axle bolt as the factory OEM axle bolt has been an issue since day one with taking recommended torque and not shearing off the flange, this will not happen with the new axle bolt I had made and there is now plenty of thread engagement as well. Now we have the wheel and axle firmly installed and centered, it's time to move onto the stoppers.

For brakes I discovered the 950SE utilizes the same caliper/pads as the BMW HP2 E, however the use a different caliper support bracket to mount that caliper to the WP48mm, SCORE! This made life very easy with one small exception. Once I got the caliper bracket installed we discovered the caliper/pads were not centered on the rotor and would bind if the bracket was tightened down to the fork leg mounts. So we made up a few machined washers/spacers to tackle that issue and wala. Next hurdle was to clearance the new Brembro/KTM 950SE bracket so that the brake rotor hardware would clear it, 10 seconds with a grinder takes care of that as the interferance is minimal. I also discovered the KTM 950SE lower fork protectors accomodate the factory brake line just fine, however with the extra length and travel of the WP48's from the 950SE I decided to shove the forks up in the clamps by about 35mm. This still has the bike sitting 3/4" taller as there is a stiffer spring in the WP's and the fork is still functionally longer/taller then the OEM BMW HP2 E Zokes. With standard WP48's off of a KTM single cylinder, running the fork caps close to flush with the upper triple would be just a tad more ride height then stock. The biggest difference in length with the 950SE fork is the amount of upper fixed tube and overlap between the sliding stanchion. For instance the 950SE upper fixed tube is 610mm long vs the HP2 Zoke's at 573mm and KTM single cylinder WP48s at 575mm.

The second production run of 10 units is now in process and scheduled to be complete within the next 2-3 weeks, however a few of those units are already sold and awaiting delivery.

$850 is the price for the following:

New lower custom triple clamp clear anodized
New wheel spacer
New modified brake caliper braket and 2 spacers with bolts
New axle shim to adapt OEM BMW axle to WP48 forks
New axle nut for more thread engagement, much stronger oversized flange.

You'll need to decide which WP48mm fork suits your needs. 950SE forks are the preffered drop-in fork IMHO, however any WP48 with single brake rotor from a KTM since 2000 or so model year will work wonderfully after a proper spring and re-valved along with setting them up for the proper travel desired (270mm to duplicate OEM Zokes and I wouldn't go over 290mm myself). I've seen 2003 take off forks for less then $400, add another $200 for springs and re-valve and you're now set!

For anyone interested in new KTM 950SE forks, they are approximately $1900 and better sourced through your local dealer then myself, but I'll be glad to help out where I can!

For Advriders in the continental 48 states I'll include free ground shipping and a T Shirt!

Big thanks to Mav for hosting my pictures on his Smug Mug, I've not been able to open them or do anything but email the originals.
Just some dude on the internet,..

Some Dude screwed with this post 03-15-2011 at 02:49 PM
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