The Spoke Curriculum - Session 5

Wheels

Description

True, spokes

Content

Primary Content

Instructor Notes

"Spoke tension is used to keep a rim straight, centred, and strong. Uneven spoke tension is often needed to hold a rim straight (if the rim has been previously bent by a collision), but this leads to a weaker wheel, and will cause spokes to lose tension more rapidly from riding. A straight rim is required both for wheel strength as well as proper adjustment of brakes: if the rim is badly out of true (not straight), then brakes can't be adjusted tightly without rubbing. Uneven spoke tension and corroded spokes are more likely to break. To check for the true of a wheel, spin the wheel and watch the distance between the rim and a brake pad. Don't look at the rubber tire: imperfections in manufacturing, as well as imperfect mounting can make a tire appear to wobble back and forth, even on a straight rim. If the rim is within about 1mm of lateral true, it is sufficient to ride, though many mechanics and cyclists have much lower tolerances, and will aim for no more than 0.1-0.5mm of side-to-side variation. Check for roundness as well: watch from the side and observe if the rim appears to hop or dip up and down as it's spinning past the brake pads. If the rim requires truing, see http://www.parktool.com/blog/repair-help/wheel-and-rim-truing Wheel truing is a bit of an artform, best learned through practice and experience. Many old and damaged wheels can't be fully trued, and spokes will often seize in spoke nipples. Be very careful to select the smallest spoke wrench that fits the spoke nipple, and to fully engage the spoke wrench before turning, as the spoke nipples round off very easily."

Specific Skills

Repair Skills

Skill	Content	Reference
Truing		http://www.parktool.com/blog/repair-help/wheel-and-rim-truing

Hubs & Headset & Bottom Bracket

Description

Checking for play

Details

This is normally one of the most critical pieces of knowledge for a mechanic, since nearly every moving part on the bike involves this adjustment

Content

Primary Content

Instructor Notes

If there is lateral (side-to-side) movement or "play" in the wheels, cranks, or headset, or if any of these rotating parts don't turn smoothly and freely, then adjustment is required. The principle tends to be the same for all of these parts, though the tools vary. Hub adjustment Remove quick release skewer and springs. Remove any rubber boot covering left side cones and locknuts. On a quick-release wheel, insert skewer through cog side of hub. Install quick release adjusting nut on non-cog side. There must be a gap between the skewer adjusting nut and the locknut. The quick release nut must press only on the axle, not on the locknut. Place cog side of wheel into left rear dropout. Non-cog side sits outboard of the bike, and is accessible to mechanic. If the cogs touch or interfere with the frame, remove rear cogs. Front wheel: either left or right side goes to rear dropout. Adjustment is done from side opposite clamped side. Adjust quick release until tension is same as when normally clamping wheel in bike. Resistance to closing should begin half way through swing to fully closed. Check bearings for play. Hold end of axle on non-cog side with one hand and rock rim laterally with other hand. Play in bearings will be felt as a knocking in the axle. If no play is felt, adjustment is potentially too tight. Purposely create bearing play as the first step to proper adjustment. Use a cone wrench and hold cone from moving. Use another wrench on locknut. Turn locknut counter-clockwise to loosen. Loosen cone by turning cone wrench counter-clockwise about 1/4 turn, or 90 degrees. Hold cone from moving with cone wrench and tighten locknut. Locknut must be fully tight before play can be checked. Test for play by holding axle and moving rim laterally. If play is felt, adjustment is too loose. Tighten adjustment: Use a cone wrench and hold cone from moving. Use another wrench on locknut and loosen by turning counter-clockwise. Recall angle of cone wrench and tighten adjustment by turning cone clockwise. Imagine cone wrench extending to the rim. Move end of wrench only the distance from one nipple to the next at the rim. Hold cone from moving with cone wrench and tighten locknut. Locknut must be fully tight before play can be checked. Test again for play by holding axle with one hand and moving rim laterally with the other hand. Rotate wheel and check for play all the way around wheel rotation. If play is still present, repeat adjustment step above until play just disappears. Remember to make small adjustments clockwise one at a time. Check for play at rim after each adjustment. It is likely it will take several small adjustments. Once play has disappeared, test final adjustment. On a quick-release wheel, open skewer partially (about 45 degrees) and check again for play by rotating wheel and checking several points. If play is felt during this test, hub is adjusted.

Specific Skills

Repair Skills

Skill	Content	Reference
Hub overhaul and adjustment		http://www.parktool.com/blog/repair-help/hub-overhaul-and-adjustment
Adjustable bottom bracket service		http://www.parktool.com/blog/repair-help/adjustable-type-bottom-bracket-service
Cartridge bottom bracket service		http://www.parktool.com/blog/repair-help/cartridge-bearing-type-bottom-bracket-service-bbt
One-piece bottom bracket service	(many BMX bikes)	http://www.parktool.com/blog/repair-help/one-piece-bottom-bracket-service
BMX detangler adjustment	(allows the handlebars to be spun 360 without entangling cables)	http://www.parktool.com/blog/repair-help/bmx-freestyle-detangler-adjustment
Threaded headset service		http://www.parktool.com/blog/repair-help/threaded-headset-service
Threadless headset service	(more modern, higher-end bikes)	http://www.parktool.com/blog/repair-help/threadless-headset-service