Fork Stiction Tuning
by Mike Nixon
Just a reminder: The first half of this procedure--the "blue-printing" stage--can only be performed on forks which have the requisite Teflon bushings, which means those manufactured since about 1979.
STEP ONE: BLUEPRINTING
Disassemble the fork completely. Lay the parts out on an old towel, wash with brake cleaner and wipe clean. If someone has put a piece of foam on top of each fork seal, throw the foam away. Honda themselves recommends this in a pair of bulletins sent to dealers, because the foam, intended to keep the tube oiled and so help reduce stiction, instead gets caught in the seal, making the fork leak profusely.
Cut some V-blocks from short pieces of 2x4 to lay the tubes on, and spin them to see if they're bent. If so, get them straightened. If they've been straightened, or the bike has been crashed, look for creases, which if found relegate those parts to the dumpster. Also check them for scratches or nicks, neither of which is fixable: the seals will always, always leak. And use only stock tubes. Nothing else even comes close to OEM quality. Examine the Teflon bushings for wear. If even a little of the black coating is worn off, replace them.
Onto one tube, install the new Teflon bushings and the slider, using a fork seal driver to get the upper bushing all the way in. Don't install the seal or dust scrubber. Clamp the tube in a vise (protect it from the jaws) and rock the slider side to side to feel (and even hear!) the clearance.
We're going to take most of that out, using the Pierre DesRoches/ Joe Minton bushing procedure outlined in the January 1985 issue of Motorcyclist magazine ("Deslopping Your Sliders"). Disassemble the fork leg, remove the bushings, and slip the upper one onto a closely-sized piece of pipe (an old fork tube is best) and lightly dimple the outside of the bushing with a center punch. This increases the bushing's thickness, snugging its fit between the tube and slider.
After dimpling, gently clamp
the bushing in the vise and hacksaw 1/32" out of its gap.
File the raw edges smooth and lay the bushing aside.
Clamp the tube in the vise and wrap a 0.001" feeler gauge around the groove that the lower bushing fits into before slipping the bushing back on. This tightens up the lower bushing.
Install the slider and upper
bushing again (use the seal driver) onto the tube and clamp the
assembly in the vise once more to check for slop. If the slop is
gone but the fit is too tight, remove the slider, and the
bushings, and file the dimples slightly and/or cut back the shim
with scissors (do one and retry for slop, but not both unless
it's necessary), and rebuild and retest. If on the other hand
it's still loose, repeat the process above. Continue tightening
the clearances (and if you go too far, loosening them,) until the
slop is gone, yet the action is still smooth. This can take a lot
of time, but it's worth it. In fact, I'll warn you that
perfection is elusive. What happens when you remove that last
little smidgeon of excess clearance, until the fork has
absolutely no side play, is it feels good in one spot but binds
in another. The fork will be harsh. This happens because mass-produced
fork parts are not perfectly round, straight and perpendicular. A
thousandth of an inch irregularity, compounded by three
dimensions and repeated in countless places, produces a product
that ultimately needs ten thousandths worth of slop just to work
freely. Our goal is to remove the few thou it doesn't need, down
to that last thousandth. Take your time; it's an exceedingly fine
line we're treading; we're basically hand fitting the parts. Go
slow. Be thoughtful and methodical, and don't move on to the next
step until you're satisfied with your optimum balance of
smoothness and slop reduction.
STEP TWO: STICTION TUNING
If you've ever pushed a heavy box full of stuff (motorcycle parts?) across a garage floor, you've noticed it's harder to get it moving than to keep it moving. You've learned a lesson in stiction. The word "stiction" is a contracted form of the words static and friction. That's what your fork has: a tendency to bind. It's the nature of the beast. But the stiction in your bike's fork can be reduced, and so easily, and with such remarkable results, it will surprise you. Start by sanding the i.d. of the dust scrubbers with 80-grit emery paper. Keep sanding and trying their fit (each time washing very carefully) until they literally fall down the tube. Next, take your fork seals to a bearing house and ask for 2-lip replacements.
Factory seals are triple-lip,
designed to seal air forks. In a later tutorial, I'll show how to
wean your fork from its dependence on the Schrader valve, which
among other benefits will en- able the use of looser seals. The
bearing house's will probably be a little thinner than the
original, but that's okay.
STEP THREE: ALIGNMENT TUNING
Assemble the fork, leaving out the oil and springs and the wheel and fender. Very lightly snug the triple clamps. Bolt in the axle, tightening it in its clamps without the wheel. Pay close attention to the axle clamps (those arrows go forward - tighten the front nuts first), using normal torque. Now raise this axle /slider assembly all the way to the top of its travel and let it go.
Does it drop to the bottom of its travel unaided? If it doesn't budge, you've got some serious binding somewhere. If it's just a little slow, remove the axle, loosen one of the damper rod's allen bolts (either one), turn the slider 90 degrees, retighten the bolt, replace the axle and try the drop test again. Repeat as necessary, tuning one or both damper rods, until you achieve maximum "drop speed." Take your time. Next, tap the top of one of the fork tubes with a soft mallet to move the tube downward in its clamps a smidge (0.010"-0.020") and try the drop test again. If there's no change, tap some more. If still no change, raise the slider/axle assembly all the way to the top of its travel and tap on the bottom of the leg upward, which will move the tube upward in its clamp, and check with the drop test again. Try with the other leg also. Do you see what we're doing? We're hunting for the best alignment. Because of manufacturing tolerances, the best internal alignment may very well occur when one of the fork tubes is incrementally higher than the other. Say 0.050"-0.080". That's okay. It's far more import- ant to align the fork's parts internally, than it is to worry about what they look like on the outside. Just remember to fully tighten the triple clamp bolts when finished. At this point, try the front fender. Install it and do the drop test. Don't let the fender influence fork movement. Reshape its inner bracket, shim between the fender and the sliders--what- ever it takes to get the same drop speed with and without it. Stiction tuning makes a world of difference. Be sure to do all of the steps in order.
"Whoa...this is a lot of
work!" you say. Doesn't the proverbial 'Loosen the parts and
pump the fork until it squares up' routine work as good?"
Actually, compared to this procedure, that's whistling in the
Text and illustrations © 1985-1997 Mike Nixon