Eight Basic Fork Tips

compliments of Hoyt McKagen's BEST Motorcycle Repair

XL head repair, cylinder boring, custom machine work.




1) Check upper stem bearing fit on stem; if it can be wiggled at all it's loose and will affect the handling drastically. Loctite will do in a pinch to tighten it up if you're fast at adjusting bearings. Stock stems are tubing whanged into shape, meaning they're soft and thin. Far better is new thick-walled well-fitted precision made stem. Replace bearings if needed.

2) Remove springs, wheel and fender, drain your fork oil and flush and try the fore-aft play of each slider on tube at several positions. If they have as much as 1/40" or .6 mm movement at axle end the bushings or sliders are worn and need renewing.

3) Make sure seals and dust boots aren't dragging; you can take seal garter springs out and run w/o dust boots if indicated. 

3a) Better damping valve response by shimming the parts will usually improve fork action. Use CPSO fork fluid, which has polymer- and metallic-based antifriction additives and really reduces stiction. 

4) Remove tubes, hone fork clamp eyes with a bra ke hone just enough to get paint and mung out, clean eyes, pinch slots and tubes thoroughly with carbie spray, air dry or wipe with dead clean paper towel, and re-install w/o touching mating areas. Trash the pinch slot stop washers if you have them, use torque wrench on the clamps and don't go over the values given. 

5) Check rim play to see if your wheel bearings are properly fresh and tight. Ideally you set up wheel bearings by measuring lateral play of axle, torqued, then change exactly that amount by precision shimming outer race or trimming spacer. 

6) Check balance w/ tire off first as this is sign of out-of-round wheel; if this shows up check rim with dial indicator and true it as needed. Tighter spokes won't loosen up when bedding in but tension doesn't improve wheel stiffness and too tight means more broken spokes. 

7) Make sure SH bearings are not overtight; I'll repeat: set proper preload on first inner nut and then on outer nut, then BACK OFF the inner to lock it. If you do the opposite you've put extreme preload on bearings because of slop in the threads. This way it's consistently set and easily adjusted tighter or looser. 

8) Paint doesn't withstand pressure well and always causes creep in joints, so clean it off at points where axles clamp into fork and swingarm or mating surfaces of any other bolted joint. Careful assembly of fork is a vital point and you must leave springs out til last so you can continually try the travel as you build, correcting anything like fender mounts that pull. 

8a) Fork alignment is checked easily and accurately by sighting between tubes at illuminated background and moving head til the tubes overlap. If not parallel there will be point of light between them that moves up and down. If parallel, the light will wink out at once over the entire visible length. 

8b) Two words ... fork brace.

Hoyt McKagen, November 29, 2000.