At the Bench: Cone Nuts

This morning (as I write this, not the morning you’re reading this), as my eyelids fluttered me into consciousness, I had a flashback to the shop where I developed my wrenching chops. Once my combination smile/shiver passed I felt the heft of Var cone wrenches in my hands. In fact, what I recall feeling was one cone wrench in each hand and a box wrench also held in one hand.

Why so many wrenches? Unlike nearly everything else on a bike where I could simply slot an Allen key into place and turn either tighty or loosy, a bicycle wheel’s cone nuts were arguably the most frustrating adjustment to make on a quality bike. For those of you who joined this show after Lance Armstrong’s first Tour de France win, it used to be bicycle wheel hubs didn’t use precision bearings; they employed traditional cup-and-cone bearings, complete with loose balls that could scatter to the four corners of a shop floor like so many of Charlotte’s baby spiders being taken by the four winds. And for those of us who never quite got over the loss of mudpie making as a legitimate recreation, squeezing Phil Wood grease into a bearing race was a sublime pleasure.

And if you’ll permit a momentary digression, I have to laud those Var wrenches for their style. The Vars were heavy, heavier than the chromed ones Park offered at the time. They were also harder and unlikely to be damaged through misuse. They hid beneath a dark patina that belied their precision and strength and the outer contours of the jaws had an artfulness to them that recalled creations from the art nouveau period, a flourish only the French would bother to twirl. To look at them I knew that whoever designed them didn’t only have engineering one their mind. They didn’t want to pick up an ugly tool.

I still haven’t answered why so many wrenches. But I’ll get around to it, I promise.

It used to be that the three kinds of bearings used in a bicycle—hubs, headset, bottom bracket—were all cup-and-cone and required a sensitive touch to establish whether they were too tight or too loose. If the bearing was loose, there was a risk that the balls would roll out of position and damage the races, but if the bearing was too tight, the pressure on the balls would grind them into the races. Either option meant bearing death.

With cone nuts the challenge of tightening them properly was, hell, I’m not sure how-many-fold, but a bunch. First was the fact that the washers between the cone nut and lock nut did not prevent tightening a lock nut from tightening the adjacent cone nut. The solution is to put a wrench on both the lock nut and the cone nut, right? Only partly. With the two wrenches in place, there was no way to know if turning the locknut was actually tightening it or if the cone nut was loosening, or if they were both turning in the same direction. This last option was what happened most often once the two nuts were more than hand-tight against each other (even with that next-to-worthless washer). Honestly, that washer’s greatest value came in how it provided a bit of space between the lock nut and the cone nut, so that the jaws of the two wrenches didn’t catch against each other.

The solution, then, was to hold the axle in place by place a cone wrench on the opposing cone nut. Hence, two cone nuts and one open-ended wrench.

To execute the move, what I learned to do was position the cone wrench on the fixed cone at 3 o’clock. I’d then spin the opposing cone until it was hand-tight, slide on the washer and spin on the lock nut until it snugged the washer. I’d then take the open-ended wrench and cone wrench and slide them into place, positioning them so that the cone was at 3 o’clock and the open-ended wrench was at 1 o’clock, the idea being that tightening would involve squeezing the box wrench toward the cone wrench, all while holding both cone wrenches perfectly still.

Once the lock nut was tightened to maybe half the tension necessary not prevent everything from loosening on the next 1000 miles of riding, I’d remove the wrenches and check tension. Here’s the part that’s especially crazy: I’d check to make sure that the bearing was ever so slightly loose. What I was looking for was a just-perceptible play in the bearing when I put a perpendicular load on the axle—I wiggled the axle up and down. If there was no play, I’d simply turn the two cone nuts away from each other; because the lock nut wasn’t fully tight, it would turn with the cone. I’d back a roughly 1/16 turn and try again. If there was too much play, I’d grab a crescent wrench (I had only one 15mm open-ended wrench) and turn the two lock nuts toward each other.

Once I had the adjustment dialed, I could then tighten the lock nut the last eighth turn against the cone nut. Once tight, I’d verify that there was still play in the bearing.

So why was I leaving play in the bearings? The quick release. It turns out that once clamped in dropouts at an appropriate tension, the slack in the bearing adjustment would be eliminated. I’d verify this by again placing an angular load on the bearings, this one by wigging the wheel perpendicular to the plane of the bike.

Honestly, I miss the days where the quality of a mechanic’s work depended on what they knew in their fingertips.

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