Tuesday, January 10, 2012


This was a fast afternoon project, the most complicated and time consuming part is making it look nice afterward. I wanted my top-knot-port to look at least somewhat clean and finished, so I used a relatively nice helmet and used the existing covering to hide the edges on the hole.

The bit dangling behind the hole is the rear strap for the helmet.
If you want to do this at home, the steps are easy: grab a helmet, cut the seam in the fabric covering and move it away from wherever you're drilling the hole. Drill a huge hole using a 3" hole saw and a drill with some oomph (drill out just the hard plastic layer, use a knife or hot wire to cut the foam). Spend the next two hours using double sided carpet tape, super glue and an Xacto knife to tape the fabric into place, glue the seam back down flat, trim it and tuck it under the hard shell to get a nice clean edge on the hole. Stencil a stripe and your initials on it, as if somehow someone might mistake it for theirs.

Note the not-sewed seam: super glue works wonders, and looks fine.

I made this helmet so that I wouldn't have to take my top knot out to go on test rides at work. Yes, this is incredibly dorky, yes it does void the warranty, yes it is less safe overall now. But...I have yet to hit my head while on a test ride (knock on wood) and in my non-test ride head-ground interactions, the top back of my helmet is unlikely to go directly into the ground. Usually it's the back or side. Usually. If you do this, it's your own fault if anything goes wrong: drilling a hole in your helmet is clearly a bad idea.

Monday, January 9, 2012

Perry Coaster Hub

A friend of a friend asked me to check out a Perry coaster hub and make sure it was ridable. Unfortunately for them it isn't, but I ended up keeping the hub as a little history project.

Perry B-10 disassembled. Note damage to cone nut in upper right.
 My best guess on the model and manufacture date for this hub is that it is a B-10, made in 1955. The model "B" is stamped on the inside of the reaction arm, and 10-55 on the other. Some additional support for the 1955 date is the brake cylinder stamped "Perry 4-55." The later model 100 had "B-100" stamped on the outside of the arm, under the two stars. It also had a different brake cylinder design, using a spring running in a channel around two brake shoes as opposed to the v-split with internal spring used in the B-10.  All Perry hubs feature a "xx-yy" stamp on the shell which designates the number of holes and spoke gauge for that shell (in this case 36-13).

Date stamp (?) on Perry reaction arm.
Modern coaster brake hubs generally use a clutch that expands the brake or engages the hub shell, driven by a screw on the driver. Below the clutch can be seen between the brake cylinder on the left, and the right hand set of ball bearings. An important feature is the constriction of the hub shell on the right: this is where the clutch engages the hub shell when pedaling forward.

Coaster brake hub with shell sectioned. Image via wikimedia commons.
The Perry is different in that the hub shell has (with the exception of the races on either end) the same internal diameter throughout. Rather than the driver moving the clutch to engage the shell directly, the driver has a set of ramps which push five roller bearings into the shell. This locks the two together under significant frictional force, and transmits the pedaling load without slipping.

Perry parts listing. Via Rat Rod Bikes.
 When the driver is rotated in the opposite direction the rollers retract and are trapped against the roller cage, driving it so that the roller cage cam forces the brake actuator into the brake cylinder, expanding it slightly to engage the hub shell. The brake actuator itself has a pair of roller bearings which expand outward when braking. The brake cylinder is fluted internally to receive these bearings, which further expand the brake cylinder. The drawback to using the roller bearings to expand the brake is asymmetrical expansion of the brake cylinder, which can be seen in the difference in wear between its drive and non-drive sides. In theory this could produce localized heating and brake fade or poor brake engagement, but I was unable to locate any accounts of this in a quick search.

This design has since fallen out of use, but was one of several competing designs found in the mid 20th century. In the 1970's it was so uncommon in the States as to go unremarked in the 1973 "Glenn's Complete Bicycle Manual" which is, as the title states, quite complete.  Sturmey Archer released a similar design in 1963 as the SC, and it was produced until 1978, however I have yet to come across any of these hubs. Successors to the SC (the SC1 1978-80 and the SCC 1978-82) replaced the roller bearing design with a cone-clutch design similar to current coaster hubs. As far as I can tell the SC and Perry (B-10, B-100) hubs were largely found only on English bicycles, with their import to the US being limited. Verifying some of the claims on what hub was on which make/model of bike is possible, but not easy, and is beyond the scope of what I want to dig into.

Sheldon Brown noted that the English coaster brakes have a fixed right hand cone and a square end on the drive-side of the axle, used to hold the axle while adjusting the hub. His site has a good scan of both an exploded diagram and parts list with compatibility between hubs. Something to note is that these cones are not necessarily permanently fixed to the axle, they simply lack wrench flats for adjusting.

Note the square end of the axle, a specific wrench came with these hubs for holding the axle while adjusting the hub. The fixed cone has also been loosened and un-threaded slightly.

In this particular hub, there is polishing and pitting on the driver where the rollers sit under load. The rollers themselves are largely unscathed, with the exception of chipping on the ends of the rollers where they contacted the edge of the driver. The addition of these flakes to the lubricating oil likely did not aid in prolonging the hub's life. More serious issues with this hub are the damaged brake actuator, the missing tab from the brake cylinder, and the throughly trashed non-drive-side (NDS) cone nut. In this particular design, the cone nut has two ears which engage the reaction arm, and prevent the cone from spinning under the action of the brake cylinder. One of these ears is missing, as is a large section of the cone which would have been supporting the ear. In discussing this hub with a Perry aficionado, it seems that this is a common mode of failure.

Clockwise from top left: Brake cylinder showing missing tab, and cracking around the remaining tab; Left cone with damage and missing ear; Brake actuator with crushed end and deformed drag spring; Roller bearings with chipped ends.
Despite its list of failures and weird quirks, I enjoy this hub. It has some nice touches, such as a snap-ring on the driver that prevents the roller cage and the rollers from coming off the driver when you're assembling the hub. The driver is a pretty unique part, and in theory should work well. In practice there are a few material and design defects that make it a bit iffy. Even if this hub were in working condition, I don't know if I'd want to ride it due to the potential for various bits to fail suddenly, but it makes a nice addition to my collection of broken hubs.

Robert Alverson 2012, CC BY-SA 3.0. All images and logos property of their respective owners, unless listed otherwise images were taken by the author.


http://en.wikipedia.org/wiki/File:R%C3%BCcktrittbremse_geschnitten.jpg Sectioned coaster brake hub image from wikimedia commons, posted by user Stahlkocher. CC BY-SA 3.0

Rat Rod Bikes has a few threads on the Perry hubs, the one linked is a sectioning of a B-100. Image of the Perry parts listing is from the linked thread, which cites classicbicyclefanatics.com as the source. I was unable to locate the original there.

http://sheldonbrown.com/coaster-brakes/sc.html Adjustment tips and parts listing for Sturmey Archer SC hub, and parts compatibility with other makes.

www.sturmey-archerheritage.com Sturmey Archer timeline, hub production dates, exploded views and parts lists.

Additional information:

Grace's Guide on Perry and Co. A short time-line of the company, which was in the business of pen nibs before entering into bicycle and motorcycle parts.

Mark Gell's scan of the Hercules service guide for the Perry hub.