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Author Topic: WP Dakar front-end conversion  (Read 13757 times)

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Offline JAmBer

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WP Dakar front-end conversion
« on: February 09, 2009, 06:37:03 am »
When I realised that my entire front-end would need to be replaced following an accident last year, I started looking at options. New forks from BMW would cost over R15k (excl triple clamps which were also damaged). The Touratech kit for WP forks on the Dakar goes over R20k. This is the kit they fit to their Rallye F650. It uses USD WP 4357 MXMA forks with custom triple clamps and other goodies. It turns out that this is the very same model fork fitted to 200-500cc KTMs in the early 2000s. The early 640 Adv also used 'em, with different springs. What a versatile piece of kit! It is a nice upgrade to the Dakar: fully adjustable for rebound and compression damping (but you have to add spacers internally to adjust preload) and travel is around 250mm (std Dakar is 210mm).

This sparked an idea. I put out a request for parts on the forum and Rufus115 responded with forks and triples lying in his backyard from a 2001 KTM 250 EXC. The project was underway!

Our fantastic postal service (sorry, I forgot: sarcasm is the lowest form of wit) managed to send box 1/2 to the correct postoffice and box 2/2 to the other side of Cape Town. After retrieving all the bits myself, I did a trial fitment of the triples. There were two sizes of triple clamps available for these KTMS: 16mm offset and 20mm offset. These were 20mm... great, less twitchyness offroad!

Rufus115 had left the lower bearing on the steering stem and it seemed to mate perfectly with the BMW's outer race which was still in my frame. The forks were of similar length to the OEM Showas and had similar axle offsets (so steering geometry would't be too messed-up by the KTM's 20mm offset triples).  It looked like this was going to be the easiest conversion in history. Or so I thought...
« Last Edit: February 09, 2009, 08:14:43 am by JAmBer »
 

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #1 on: February 09, 2009, 06:40:15 am »
During the following weeks, it became apparent that the bearings weren't mating properly. And then it turned out that no suitable bearings were available. Modifications would be required. I'd also need a custom axle for the front wheel and a means to mount a brake caliper. The steering lock (ign key) wouldn't fit either and the steering end-stop arrangements weren't compatible.

I was heading down to PE for the Christmas holidays and decided to take some of this stuff with me to see how much I could get done before work started again.

I met an incredibly helpful retired fitter/turner, John West, in Greenshields Park PE who helped me with a lot of machining over the Christmas period. His garage contains a lathe, grinder and other required machinery to turn axles 'n things and his rates are very reasonable. Moreover, he helped me during the holiday week between Chritmas and New Years. "What a legend!"

It's been a fantastic project. I have had to machine custom parts, make a plan here and there and have met a number of helpful people along the way. Without further ado, here's the first report...


Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #2 on: February 09, 2009, 06:43:43 am »
Activity 1: Triple clamp mounting

As I mentioned earlier, the KTM's steering bearings were different from the BMW's (no surprise there, really). The KTM's shaft is ~30mm in diameter, whereas the BMW's one is 28mm. The BMW's steering stem requires a 52mm race. Both bearings are unfortunate sizes that are only obtainable from specialised shops (one of 'em is in the Imperial range! Metric anybody?). I wanted to keep to OEM as far as possible so that I could easily buy spares.

The solution involved machining down the KTM's central triple to accept std BMW 320/28 steering bearings. It meant shaving-off ~1mm around the shaft. We would have to remove the shaft from the lower clamp to machine it. And I'd have to remove the original lower bearing.

The bearing wouldn't be reused, so I just cut the cage and pried it off with a screwdriver and a bit of man-handling.

In order to get the shaft out of the lower triple clamp (it is a press-fit), we had to heat it and hit it with a big hammer. Hard. Holding the thing in a vice with wood shims to prevent damage to the soft aluminium is tricky.  After that, John machined the part to size. We were cunning: you don't want to machine the entire shaft to the same size, because then you have to hit the lower bearing over the entire length of the shaft to get it to the bottom. Instead, you machine the areas where the upper and lower bearings will mount to the desired size (28mm) and then machine the surrounding areas down a little more (27.9mm), so that the bearing will slide freely along those sections.

I put the shaft in the freezer for a few hours and the bearing in the oven to heat it before dropping it into place with a gentle tap. Beautiful. FWIW, the aluminium pipe from a pool net is the perfect size for a BMW steering bearing drift.

Unfortunately, the central shaft is about 4mm too short and so doesn't fully penetrate the upper triple's center clamp. Hopefully not a big deal, because there's more than 10mm of contact area and the shocks themselves will hold the assembly together once all is tightened up.
« Last Edit: February 10, 2009, 07:19:34 am by JAmBer »
 

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #3 on: February 10, 2009, 07:19:23 am »
Activity 2: Axle

The std KTM used a hollow 15mm axle. It didn't look strong enough to hold 195kg of Dakar over bumps and under heavy braking. The stock BMW wheel takes a 17mm solid axle (which I had bent spectacularly in my spill, btw). Rufus115 provided me with a KTM hub along with the forks and since I had to replace the entire wheel anyway, I had the option to go with a BMW or a KTM wheel.

Now I have an aversion to non-standard things. BMW use bog-standard 6203 bearings in their F650 hubs. This is the same part that you'll find in everthing from the Bosch alternator in a CitiGolf to the washing machine in your laundry. You can buy 'em at any hardware/autoparts store. The EXC's isn't.

I wasn't willing to forego the ABS since I believe this played a pivotal role in saving my life. Fitting the ABS sensor ring to the KTM hub would be painful. Also, the EXC's brake disc was much smaller than the standard Dakar's. So I'd be fitting a BMW wheel.

With that decided, I enlisted the help of a few friends, including a mechanical engineer to try'n come up with a plan to do this in the simplest way possible. Then I went to visit John again. He produced some high-tensile steel (from an old McPherson strut!) and we proceeded to make an axle: the one end is 20mm which mounts directly to the left-side of the WP forks. The right side requires a shim because it's larger (~25mm). The original KTM arrangement had one for the 15mm axle too. This was simply cut shorter and machined out to 17mm ID. We then cut a thread on the 17mm end of the axle into which screws an M10 bolt for locating the assembly.

Then we needed some spacers to correctly locate the hub in the center of the fork. It was only ~1mm off center, so I just used an ordinary flat-washer. Measuring this offset was a tricky engineering exercise that involved three T-pieces, 4 hands and lots of patience!

Offline letsgofishing

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Re: WP Dakar front-end conversion
« Reply #4 on: February 10, 2009, 07:27:53 am »
That's some project you've taken on there!
Hope it all goes smoothly for you  :thumleft:
There is nothing you can do about the past and you can't predict the future...all you have is the now...live it to the fullest.

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Offline lonerider

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Re: WP Dakar front-end conversion
« Reply #5 on: February 10, 2009, 07:34:03 am »
Interesting reading! Sounds like a great engineering challenge - congrats on all so far, hope the rest works out smoothly.
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Offline MrBig

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Re: WP Dakar front-end conversion
« Reply #6 on: February 10, 2009, 07:34:09 am »
I really admire this type of project - there are no definites and you need to be (or know) McGyver to make it work
Looking forward to the next installment   :thumleft:
 

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shark_za

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Re: WP Dakar front-end conversion
« Reply #7 on: February 10, 2009, 07:37:32 am »
Watching this thread in anticipation.
 

Offline the_BOBNOB

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Re: WP Dakar front-end conversion
« Reply #8 on: February 10, 2009, 09:32:06 am »
nice work - cant wait to see the end results
 

Offline growweblaar

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Re: WP Dakar front-end conversion
« Reply #9 on: February 10, 2009, 12:53:42 pm »
<subscribe>
 

Offline Iron Shark

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Re: WP Dakar front-end conversion
« Reply #10 on: February 10, 2009, 01:28:11 pm »
looking good!
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Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #11 on: February 11, 2009, 07:08:40 am »
Activity 3: Trial mounting and clearance checking

At this stage, both the wheel and the triples all fit together on the frame correctly, but I couldn't turn the handlebars to full lock 'cos the upper end of the WP's are much wider than the stock BMW stanchions. It was catching on the dashboard/headlamp frame mounting. It was only by a few mm, so I just ground it off with a pencil grinder and resprayed the area with primer and satin black.

A quick check of the other surrounding bits (radiator, plastic intake manifold, air duct for oil reservoir) revealed that their clearance was sufficient.

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #12 on: February 11, 2009, 07:15:13 am »
Activity 4: Brake caliper mounting

The BMW caliper bolts onto the front left shock with a different bracket to the KTM, but both are Brembo parts. In fact, the BMW F650, KTM640, 950 and 990 all seem to use the exact same floating Brembo caliper with different adapter plates to mount onto their respective forks. I was nervous about this part of the conversion because in the Touratech kit this was a custom manufactured part (and I figured they wouldn't custom manufacture something unless it was really necessary). I polled Touratech for a price: R2k for the aluminium bracket alone and it would take over a month to manufacture and ship to SA. That was out of the question: my budget didn't allow for it and I was too impatient.

So I started asking questions about having a suitable part manufactured locally. Turned out to be more trouble than it was worth. It would be of comparable cost to have it done properly. And I wasn't willing to take shortcuts with such a safety-sensitive component.

Then I decided to take a closer look at what KTM had done. First-up was the early model KTM640Adv. This had larger discs (320mm vs the Dakar's 300mm) and the bracket looked a little different in the pictures. But it turned out that the KTM950's two front discs are also 300mm and eyeballing the brackets at KTM CT looked about right. Secondhand KTM parts are scarcer than hen's teeth and I was rather dissapointed when, after finding one on ebay, I lost the bid in the last few minutes of the auction. Ordering one locally would set me back over R1k and would take 4-6 weeks to import from Europe. Eventually I bit the bullet and ordered one online for R750 and it arrived the next week in Brembo-branded (not KTM) packaging with instructions in Italian!

Everything bolted together without any hassles using standard M8 bolts. I would like to use stainless steel allen-cap bolts here too, but I need to be careful of the tensile strength of the chosen bolts, because this is a safety issue.

The remaining problem which I have not yet solved is the ABS sensor mounting. I think I'll manage it simply by bending a piece of steel plate and drilling a few holes. This will just bolt onto one of the existing brackets. The only trickery is that it needs to be mounted very close to the sensor ring (0.1mm to 0.9mm, apparently). Those are tight tolerances for me to achieve with a piece of steel and a 4lb hammer... I'll attempt this once the bike is assembled.


Offline bushclown

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Re: WP Dakar front-end conversion
« Reply #13 on: February 11, 2009, 06:58:22 pm »

Looking good
Going to be a great step up when done
 :thumleft:
 

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #14 on: February 12, 2009, 07:01:33 am »
Activity 5: Handlebar mounts

Now the BMW uses a thin ~22mm handlebar, but the EXC uses an oversize ~28mm bar. I wanted to keep the BMW handlebar because the heated grips require a little cutaway on the bar-ends for the wires, and I wasn't about to toss those babies - they're fantastic for those cold winter mornings! I couldn't find an oversize bar with the required cutouts at the time, so I decided to make a plan to refit the BMW bars.

Rufus115 included the KTM handlebar mounts in the suspension deal so I could mount the BMW handles by machining a couple of 22->28mm adapter shims. But the KTM bar mounts use only two bolts and I was worried that the forwards/backwards forces on the handlebars would produce too much torque on the narrow mating area. There are four holes in the upper triple clamp, but only two are used at any one time. This allows you to adjust the handlebar distance. My suspicions were confirmed when I took a closer look at the KTM upper triples and saw that the one end was angled and had become slightly rounded from a lot of forwards pressure on the handlebars.   I decided that I wanted to use all four together for extra strength.

A second reason for not using the standard KTM mounts are that the handlebars would be quite low. As it is, I've been mooning over a set of handlebar risers for many months. I figured this was a good time to kill two birds with one stone. Build suitable handlebar mounts that are stronger and higher!

I headed back to John for a solution. We cut up a thick aluminium plate to produce two pieces that would form an adapter. These bolt to the upper triple clamp using all the existing bolt-holes and form a flat base onto which the handlebar clamps can bolt. Then I ran to the nearest bike store and bought a set of generic 22mm aluminium risers. The upper half of these clamps were ground flat (they're offset by default) and flipped upside-down to mate with the custom baseplate and form the new handlebar clamp's lower cup. I then used my existing BMW parts to clamp the top of the handlebars. After spraying them black and purchasing some longer bolts, I had 50mm risers!

It occurred to me during machining that 50mm might actually be too much since the front of the bike is likely to be higher due to the longer suspension anyway. Fortunately, I can remove the central spacer and reduce the handlebar height by ~30mm should this be the case.

Unfortunately, this mounting solution doesn't make provision for mounting the little panel for the ABS and Hazard switches. I had intended to tap threads into the new longer bolts, in the same fashion as the original BMW units. But this is not easy without the right equipment and will weaken standard bolts significantly. Instead, I intend to manufacture a little bracket for it. This bracket is pretty low on the priority list right now, and I can just cable-tie the plastic switchpanel in place in the meantime, so I've moved onto solving the next problem...


Offline tok-tokkie

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Re: WP Dakar front-end conversion
« Reply #15 on: February 12, 2009, 09:17:37 am »
Jamber,
Really cool job you are doing here.  I made my own risers for my Dakar bars.  To mount the ABS switch I used stainless threaded bar with little aluminium bushes to fit into the recess in the upper bar clamp & nuts to clamp it all together with the threaded bar rising up higher for the ABS switch and stainless domed nuts to hold them in place.  A suggestion for you.
 

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #16 on: February 13, 2009, 07:00:53 am »
Jamber,
Really cool job you are doing here.  I made my own risers for my Dakar bars.  To mount the ABS switch I used stainless threaded bar with little aluminium bushes to fit into the recess in the upper bar clamp & nuts to clamp it all together with the threaded bar rising up higher for the ABS switch and stainless domed nuts to hold them in place.  A suggestion for you.

And that's why I love this forum! Great idea, tok-tokkie, thank you! This might very well turn out to be an easier mod. I did just notice that the WP mountings are further apart than the OEMs. So I'd need to enlarge the holes in the switchpanel a little bit (only a couple of mm - and I'd probably have to do that to take the larger bolt anyway).

Do you perhaps have any extra of those aluminium bushes lying around?
« Last Edit: February 13, 2009, 07:01:14 am by JAmBer »
 

Offline JAmBer

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Re: WP Dakar front-end conversion
« Reply #17 on: February 13, 2009, 07:04:37 am »
Activity 6: Suspension service

By this stage I was confident that we'd be able to make a plan to make the WP suspension fit. I then turned my attention to its health.

Rufus115 had warned me that one of the oil seals was a little suspect, so I decided to replace both. Bearing Man sell oil seals too, so this was my first stop. The salesperson took one look and exclaimed "That's a high pressure gas seal". She then pulled out a vernier... "and it's a special size, where is it from?" Argh! KTM agents in PE only had one oil seal and I wanted to replace both. KTM CT helped me out, but these things are pricey: R480 for the two! I decided not to replace the dust seals; they are similarly priced and still looked ok.

There are a number of how-to guides for servicing the 4357MX and 4860MX forks (which are basically the same AFAICT, apart from their diameters and two internal bushes) so I won't go into detail here.

After stripping the whole thing down, I discovered that they were suffering from the dreaded WP rebound pin seizure though. Fortunately, plenty of Q20 and delicate taps with a hammer and pins freed them up without having to take apart the lower valves. I then also saw that no preload spacers were installed. Playing with some of the online spring calculators, and thumb-sucking the weight on the Dak's front-wheel, I determined that I'd be needing some stiffer springs. I will wait 'till the bike's fully assembled so that I can measure the weight distribution properly before ordering replacements though.

Then I reassembled. A little extra oil was added to stiffen the forks a bit, filling to 100mm below the top level rather than the recommended 120mm. This should help with the fact that the springs are very soft (specc'd for a much lighter bike) until I can get some stiffer springs. I also used thicker SAE10 rather than SAE5 to increase damping. The various bike forums are full of greatly varying reports about how much oil I'd be needing to refill these shocks, so I bought 3l to be on the safe side. Turned out to be uneccesary; I used only 950ml. This is probably because I managed to do it all without spilling a single drop though. A syringe with attached pipe of appropriate length works very well for setting your required oil level.

No pictures here, unfortunately. That's a bit of an anti-climax for a friday, eh?

Offline melvman

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Re: WP Dakar front-end conversion
« Reply #18 on: February 13, 2009, 08:58:47 am »
This is a mammoth project. It's one thing stripping and then reassembling the same bike some months later, which is a  task in itself when doing this for the first time. When it involves modifying another bike's parts to fit, it does become a "Macqiver" project. Good luck and keep this forum informed of your progress.
 

Offline Poffmuis

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Re: WP Dakar front-end conversion
« Reply #19 on: February 13, 2009, 01:09:25 pm »
this dakar is gonna handle so lekker in the dusty stuff!!!!
Looking good  :thumleft: