Sturmey-Archer SW Drei-Gang-Naben: Unterschied zwischen den Versionen

Make sure burrs on the pinion teeth are ground smooth. If the burrs face the spacer ring (L6), it will experience excessive wear and probably an increase in drag until the parts wear in. Allowing things to wear in on their own can really chew up the spacer ring, however, so I suggest removing any burrs from the planet teeth.

When rebuilding an ailing SW, the best approach is to use all new parts, but most of these parts are rare today, so this is not a viable option for most hubs. However, with a collection of junk hubs, one may be able to assemble a "better-than-new" hub by measuring the parts and selecting the best-fitting ones. Using a micrometer or dial caliper, measure the length and height of each pawl and try to match like measurements into sets of three. Also, look for a combination of smallest inner diameter with largest outer diameter of the right-side pawl ring (L11). The driver surface that this pawl ring runs on should also be the largest possible. Try the operation of the right-side pawls by hand (partially assemble the internals with the right-side bearing cone finger tight — no play) and see if you can get simultaneous engagement of all three pawls. It's frustrating, but can be accomplished. Also, select bearing cones whose threads fit as tightly as possible on the axle to help eliminate gear misalignment (same cones as the AW, so availability should not be a problem). Ultimately, the "best" combination of parts will be a matter of judgment and trial-and-error fitting. If you do not have any spares to work with, converting to spring-loaded pawls may be the answer — see below.

This is best accomplished with a small sharpening stone, light oil, and a ton of patience. The idea here is to reface the dogs to be perpendicular to each other and thus eliminate the tendency to cam out against the spring. Be careful to check the fit of the gear ring with the pawl ring before reassembly, and do not remove too much material, since the parts are case hardened, not through hardened. The case depth with carburizing methods typically used by such parts is seldom very deep, and therefore this regrinding method may not last very long. (I have heard that Sturmey-Archer used the sodium-cyanide bath method of carburizing; according to my information, this method produces what is known as superficial hardness — the case depth may be only a few thousandths of an inch)<ref>Aus dem [https://amzn.to/3oxVABc Machinery's Handbook  24th ed., Robert Green, Industrial Press, 1992 (Partnerlink)]</ref>

I am also experimenting with a reverse-taper grind and face texturing of the dogs to help keep them in contact under load. Results will be posted here at a later date.

Because most of the Sturmey-Archer internal parts are not machined or ground after heat treatment, their surface finish is rather rough, and they can benefit a good deal from polishing. Normally, this would be accomplished by simply using the hub, and all the parts would wear in over time to a smooth working condition. The problem with this in the SW is that the wear particles are in circulation, and may have detrimental effects on the pawls. Polishing of the pawl sockets, ball ring ramps, gear faces, driver, etc. can only help; polish with a Dremel tool or something similar as many of these areas as you can stand. For flat surfaces, a pane of flat glass with 600-grit wet/dry sandpaper and light oil can be used to produce a very smooth surface.

As the planet gears are shaper-cut gears with poor tooth precision, lapping of new gears is not a bad idea, either. This can be accomplished by assembling the gearing, introducing a bit of automotive valve-grinding paste in the mesh and spending a patient hour turning the assembly back and forth by hand. Don't use too much paste; you don't want to grind more than the surface of the gears. When finished, remove all traces of the grinding paste. Perhaps the best advice concerning polishing is to disassemble the hub and change the oil after a run-in period of, say, 50 miles or so. Wear areas that can benefit from additional polishing will then be evident. It may be good to disassemble and change the oil every year, or until little oil discoloration is encountered.

Another potential improvement to the design of the pawl rings would involve grinding a radius on the drive side edge of the pawl sockets. This would serve two purposes: reduce the tendency to dent the pawls, and improve the load sharing amongst the pawls. Also, on the left side, a soft steel retainer is pressed onto the end of the planet cage to provide end retention of the pawls. If three holes were drilled in this retainer at the bottom of the pawl sockets, the pawls would be more easily engaged in the ratchets because the oil surrounding the pawl could not create a vacuum effect.

A more-or-less permanent fix to the pawl problem can be obtained by spring-loading the pawls. I have successfully modified a right-side pawl ring to accept small bow-type springs in the bottom of the pawl sockets that keep the pawls positively engaged. This fix has virtually eliminated any skipping and has made shifting gears much more positive, and is probably the best long-term solution, producing a very reliable hub. If you are interested in modifying your hub, here's how to do it:

While sprung pawls may ultimately be the best practical fix, they do have one drawback. The hub will no longer be "silent" when coasting. In fact, the spring arrangement I have described gives a rather "bright" ticking sound similar to the AW's.

The closest ANSI standard-sized Woodruff key is a no. 403, but it's only 1/8th inch wide. However, in a pinch, one might be able to combine a 403 with a 203 (1/16th wide) and with careful grinding with a Dremel tool produce the correct geometry. Woodruff keys are typically rather soft, however, and pawls made from them may not last long in service. It would be good to have access to a heat-treating facility in order to carburize the pawls after shaping them.