Bike Friday is an American manufacturer of high-performance small-wheel bicycles which fold and partially disassemble to fit into a hard-sided Samsonite suitcase. The bicycle then travels as ordinary airline checked baggage, avoiding the usual inflated charge for bicycles. The suitcase doubles as a bicycle trailer.

Most parts of common Bike Friday models -- the New World Tourist, Pocket Rocket, Pocket Llama, Crusoe -- are conventional and familiar. Frame hinges are the major exception.

There is a barrel hinge behind the bottom bracket, so the rear wheel can fold underneath and then up next to the front of the frame. Some models have a second hinge, so the seat mast can fold forward. (The alternative is a telescoping, removable seat mast). A quick-release assembly behind the seat mast holds the parts together in position for riding.

Bike Friday hinges

After several years of use, the lower hinge of my Bike Friday New World Tourist started creaking as I pedaled. I discovered that a bolt at one side of the hinge had loosened. Tightening the bolt stopped the noise, but the bolt loosened again when I folded and unfolded the bicycle -- and the noise returned.

A loose upper hinge will make a clunking sound, and you may feel the vibration through the saddle.

Here's what I learned from Tim Link at Bike Friday's customer service desk and from my work to fix the problem.

The hinge has a cylindrical pin which extends through a hole (the hinge's barrel) and through tabs on either side. A bolt with a washer under its head secures the pin at each end and is supposed to clamp tight against the tab. The pin is supposed to rotate inside the barrel, so the bolts, pin and tabs all turn together. If the pin or barrel becomes corroded, then the pin rotates with he barrel and can loosen a bolt. The pin and the barrel are most likely to corrode if the bicycle is used in winter and in wet weather.

If you hear creaking or clunking, don't let it go too long, because a bolt is loosening, and it may fall off and get lost. These bolts on older Bike Fridays are only 12 mm long. As already noted, tightening the bolts only achieves a temporary fix. To put an end to the noise, you have to take the hinge pin out, clean out corrosion, then lubricate and reassemble.

Do this every year or two even if you don't notice a problem, so the hinges stay well-lubricated and don't corrode.

Note that the lower and upper hinge pins are different. Even on older Bike Fridays, where both attach using 12 mm bolts, the upper hinge pin is shorter.

Tim Link adds the following information:

Since building your frame we've changed the hinges a few times. The seat mast hinge is pretty much the same except that instead of a bolt threading in to each end of the pin itself, there's a long thin bolt that goes all the way through and threads into a self locking nut on the other side. This eliminates the problem with the bolts falling out.

Old-style hinge pin with 12 mm long bolts

Hinge pin with through bolt

Hinge pin with through bolt, assembled

This same design was used on the bottom-bracket hinge for a while, but now the bottom-bracket hinge uses a solid bolt as the pin itself, with a self-locking nut on the threaded end. These are much easier to remove, and since the bolt is stainless they don't rust into place.

Bolt as pin

There's another kind of pin used occasionally, which is composed of two "half pins" that thread into each other, with a set screw that holds them together. These are only used on the Super Pros.

Half pins with set screw

Assembling half pins with set screw

Half pins, assembled

(These are as for my 1997 New World Tourist)

• 4 mm and 5 mm Allen wrenches (separate -- not as parts of the same multi-tool), or other wrenches to fit the bolts and nuts of your bicycle. In some cases, you may need two wrenches of the same size. Check the bolts.
• Crank remover and crank-bolt wrench (sometimes needed for access to the lower hinge)
• Long 6 x 1 mm threaded bolt (old brake center bolt, for example)
• Flat-ended punch, 5/16" or 8 mm approximate diameter, or expander bolt from an old quill stem.
• Stub of 6 x 1 mm threaded rod, or bolt with the head ground down to 8mm or smaller diameter
• Hammer
• Liquid Wrench spray lube, if the pin is hard to remove
• Blue threadlock compound
• Grease

Preparation

Lower hinge of Bike Friday

1. If the pin is corroded in place, riding the bicycle may break the corrosion loose and make removal easier. Creaking is a good sign that the pin won't be too hard to remove.
2. When you are working on the lower hinge, the bicycle has to be up off the floor, so there is no weight on the rear wheel. When you are working on the seat-mast hinge, the bicycle has to be supported somewhere below the seat mast.
3. If a chainwheel prevents access to the pin on the right side of the lower hinge, remove the right crank.
4. I recommend leaving the quick release at the seatstays clamped, to hold the hinges in alignment. You may be able to avoid removing the rear wheel, but don't apply any large stresses when the rear triangle is supported only by the quick-release.

Disassembly trick: brake bolt threaded into one end of the hinge pin

Disassembly

1. Using two Allen wrenches at once if necessary, unscrew the bolt on each side. If an older-type pin is corroded in place, both bolts will unscrew, and if not, one or the other will. Set the bolt or bolts aside. Don't lose the washer(s)!
2. If only the left bolt loosened, then the pin will have to come out the right side, and vice versa. If the pin is very hard to push out, it is better to work from this step onward with the bicycle lying on its side so you can place a support under the hinge.
3. Push the pin out of the hole, toward the remaining bolt if there is one. If you have a flat-ended punch which is nearly as large in diameter as the pin, you might use that, but be careful not to mung up the flat end of the pin or its internal threads. Instead of using a punch, I threaded the long bolt from an old caliper brake (6 x 1 mm thread, same as the pin bolts) into the hole in one end of the pin, as far as it would go but without tightening it hard, and I gave the bolt head some light taps with a hammer. The pin moved! Whew. I was able to push the pin out most of the way using the brake bolt. By then it was quite loose and I was able to remove the brake bolt and push the pin out the rest of the way using the expander bolt from an old quill-type handlebar stem as a punch.

   Liquid Wrench spray lube may help to free a corroded pin. If the pin is very hard to remove, you definitely should use a flat-ended punch rather than to risk damaging the threads. Tim said that in tough cases, removing the pin might require an arbor press -- a floor-standing machine-shop tool. Using this tool requires removing the right crank, supporting the bike lying sideways across the arbor press's table, and supporting the tab on the lower side using a jig with a hole large enough for the pin to pass through . (Or send the bike to the factory...) Another option is to use a bench vise to loosen the pin, with a bolt pressing on one end aand a washer surrounding the other.

Brake bolt pushed in, pin pushed out.
Fortunately, only surface rust...

Cleaning

1. Clean the pin and the inside surface of the barrel. To remove rust, I used steel wool, and pushed it through the barrel a number of times with the stem expander bolt. A small, cylindrical wire brush on an electric drill would make cleaning the barrel easier.
2. Wipe the pin and the inside of the barrel clean with a rag or a paper towel -- pushing a wad through the hole to clean it out. At this stage, both the outside of the pin and the inside of the barrel should look moderately shiny. Don't remove too much material. In case corrosion is really bad, I wonder whether Bike Friday has oversize pins or bushings, and a drill to enlarge the barrel...

The barrel, mostly cleaned out.
Fingertip for scale. Dirt under fingernail
because I'm not afraid to get my hands dirty :-)

Assembly

The isntructions below are for the old-type pin. With the newer kinds that use a locking nut, you need only tighten the nut, then back it off enough so the hinge turns freely.

1. Grease the outside of the pin and the inside of the barrel. Avoid getting grease onto the threads at the ends of an older-type pin. Because grease will build up on the end of the pin that goes in first, it's useful to have a stub of 6 x 1mm threaded rod (for example, a bolt whose head you have ground down) threaded into it to keep the threads clean.
2. Reinstall the pin. It should slip in easily. Clean off excess grease and remove the threaded piece that kept grease off the threads of an older-type pin.
3. (If not, an older-type bolt will not secure the pin, and if you tighten the bolt, you can't remove it unless you take everything apart and clamp the pin in a vise with soft jaws. Been there, done that!) Place a couple drops of blue threadlock compound on the threads of each older-type bolt to help hold it tight.
4. Reinstall the bolt or bolts, making sure that the washer is still on the hinge bolt at each end of the pin,and tighten.
5. Replace the crank, if you had to remove it.

Finished reassembly!