| Fork Re-spring and Re-valve |
In its stock form ,the KLX250S' front suspension is under sprung for anyone weighing any more than 150 lbs. The stock spring rate is 0.38 kg/mm I've definitely have noticed the weak spring during riding. It's been especially noticeable during braking as the front end dives to the point where good control is lost.
There are several different spring rate charts and calculators out there, here are a couple: Planet KLX, MotoPro The calculation may take into account several factors: weight, riding style, skill level, terrain, etc. Speaking with your vendor of choice will help you determine the best spring rate for you. Here's a rough chart for spring rate vs. weight. Remember that the curves can be adjusted up and down based upon other factors:
| Weight range (w/o gear) (lbs.) | Spring Rate (kg/mm) |
| 160 - 180 | 0.42 |
| 180 - 200 | 0.44 |
| 200 - 220 | 0.46 |
For me, John at Moto Pro Suspension helped me select a spring rate of 0.44 kg/mm
From what I have read and heard, the proper spring will get you to about 90% of the perfect setup and swapping out the valving will get you the rest of the way. There are a at least a couple of options on the valves, Race Tech's Gold Valve Kit or Moto Pro Suspension's UltraMax Valve Kit. I choose the Moto Pro product.
A word about lowering links: After speaking with John at Moto Pro, he convinced me that my installation of the Kouba lowering links was the incorrect way to lower the suspension. He said that lowering can be done through installing a spacer in the shock. Prior to this installation, I removed the lowering links, installed the stock links and returned the forks to their normal position in the triple clamps. What I found was that the bike had "settled in" and I really didn't need the lowering links after all. Although I wasn't flatfooted on both sides of the bike anymore, it was pretty darn close. Besides I want a bit more clearance underneath as I have bottom out on berms, logs, etc. I had installed the 1.125" KLX3 link.
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Parts list:
Consumables:
Notable tools needed:
Detailed Step by Step Installation
This installation process is based upon doing the second fork (right hand side).
- If installed, remove the bleeder valve and loosen the handle bar clamps. You'll need to be able to get the 30mm socket onto the fork cap
- Before loosening the triple clamp bolts, loosen the fork cap with a 30mm socket. I found that the caps were on really tight.
- Loosen the axle clamp bolts and then the axle (17mm) and remove the wheel
- Remove the plastic fork guard and the plastic fork guard guide
- Loosen the bolts on the triple clamps (12mm), no need to remove them
- Remove the shock from the bottom. I used a trick by prying open the lower clamp with a screwdriver and inserting a couple of washers to hold the clamp open while removing the shock
- Support the shock in an upright position - my Rube Goldberg apparatus worked fine
- Loosen the fork cap completely now
- Pull the outer tube down and hold the rod nut with a 17mm wrench and remove the fork cap and collar
- Remove the spring
- Dump out the oil and pump the plunger to pump out the oil
- Remove the rod nut and note its orientation -- one side is different from the other
- Remove the metal collar and the plastic spring guide -- note orientation of spring guide
- Remove the rubber dust cap from the bottom of the shock
- Using the damper rod fork tool and a 14mm hex driver, loosen and disassemble the valve from the cartridge. This is probably the toughest and most awkward step. Using a vise to hold the shock or getting a second pair of hands may make it easier
- The cartridge can now be removed but the valve is still in the shock, I used a broom stick to pop it out.
- Disassemble the valve by removed the nut off of the shaft. The shaft was peened and the other valve parts may not slip off the shaft readily. Use a small file to lightly file the upper threads until the valve parts can be slipped off. Also, look for four small pieces of metal from the peening. Use a pointed tool to remove them, you don't want them floating around in your shock. None of the removed parts from the base are reused.
- Dress the threads until the old and then the new purple nut are easily threaded onto the shaft. The peening increased the diameter of the top of the shaft. Clean the base.
- Lay out your parts to the new valve in the order that they will be added to the shaft: base washers, high speed valving (HC #), low speed valving (LC #), green valve (oval ports go down), check plate (8mm i.d.), spring and purple retaining nut.
In my case, my HC# was 3 and the LC# was 4. Using the valve chart, lay them out from the bottom up. Either 2 or 3 base washers (the thick 2mm washers) will be needed dependent upon your HC# and LC# stackup. I needed 3, but use 2 base washers first during the test fit.
- Test fit everything first, hold the check plate up against the the retaining nut while compressing the spring. You don't want to pinch the check plate between the green valve and the collar of the retaining nut. Tighten the retaining nut down onto the green valve. At this point, the check plate should be free to move up and down along the collar built into the retaining nut. The valve stack should not be able to rotate. If the valve can rotate, then you need 3 base washers.
- Once you are satisfied with the valve, use blue loctite on the threads, lightly seat the nut and then torque it to 2ft-lbs
- Again check that the stack doesn't rotate on the shaft and the check plate is free to move.
- Now clean the fork tube and cartridge of all remaining oil. I sprayed WD-40 down in the tubes and used clean rags and a rod to swipe clean the insides. I noticed a lot of dirty grit in the area of the seal and it took several cleanings to get it all. Now is also a good time to check the seals and bushings, and replace if necessary - mine were good.
- Begin the re-assembly process - it's basically the reverse of the disassembly process. Use blue loctite on the valve threads and re-assemble with the catridge. Torque to 54 N-m
- Install spring guide (correct orientation) and collar
- Install rod nut (correct orientation - flatter side goes down) and tighten
- Support the shock upright again with the outer tube down completely. Using a fresh bottle of oil fill the inner tube completely with oil.
- Slowly pump the rod up and down fully at least five times, top off the oil each time if needed between strokes
- Now pump the outer tube up and down several times
- Let this sit for five minutes so that all the air bubbles expel themselves - top off if necessary
- Set the oil gauge to 97mm (or 114mm) and extract the excess oil - put the excess oil back into the bottle from which it came. Now a sanity check, the that the oil left in the bottle is around 460ml (or 481ml) which means that you used the specified amount of 540ml (or 519mm) Note: I don't know if 97mm or 114mm is the correct specification. These numbers come from the two different manuals. The average oil amount would be about 529ml. This isn't a big deal since in further fine tuning of the forks, you'll add or remove oil -- refer to the valve installation document, section 10.
- Install the spring. This could be a new spring with the proper spring rate. In my case, this is a new spring 0.44 kg/mm
- This part is tricky and a second pair of hands could help. Install the spring collar and cap. Screw the cap down onto the rod. Tighten and torque to 15 N-m
- Raise the outer tube and screw the cap into the outer tube - seat it but don't torque it yet
- I recommend installing a seal saver. I'm using the Tusk brand, but I turn it inside out since I don't care for advertising on my bike. Install it so that 1 - 1.5" of the seal saver covers the bottom tube.
- Install the shock back into the triple clamps (use the washer trick again) and set the height of the fork to 7-8mm -- that's from the top of the clamp to the top of the fork cap
- Torque the bolt in the bottom clamp to 25N-m
- Torque the fork cap to 29N-m
- Torque the bolts in the top clamp to 20N-m
- Install the bleeder valve and torque to 12 in-lb Don't do what I did and over torque the bleeder -- it will break very easily. I have a new set on order. :(
- Install the fork guard mount. This is be more difficult now since there's a seal saver on the fork now. Use vfrpilot's trick of using a c-clamp to get the first bolt started
- Install the fork guard
- Reinstall the handlebars - use the appropriate torque (25 N-m) and make sure to not clamp down unevenly
- Reinstall wheel - use Moto Pro's method of installing the axle, then install the axle clamp and nuts, but do not tighten down the nuts yet. Torque the axle to 88 N-m. Let bike down off of the stand and bounce on it to ensure the axle and lower fork tube self center. Now torque the clamp nuts to 9.8 N-m
- Set the base line for the compression adjuster to 11 clicks out (first turn the adjuster fully clockwise, then ccw 11 clicks)
- Replace dust caps
You're done! Now follow the recommendations in Moto Pro's installation notes for further fine tuning your fork shocks.
It's bitterly cold outside and the snow just won't go away. I'll update this report once I'm able to get a ride or two in.
Wednesday, October 22, 2008
