It's Spring

...and that means it's time again for people to bring really strange things into the bike shop.



This poor bike was out for its first ride of the season when tragedy struck. Its owner had stored her gloves and arm warmers under the saddle in case she needed them on her ride. When the gloves and arm warmers fell out, one of the gloves got caught in the rear derailleur and cassette. This instantly stopped all motion in the drivetrain, probably causing her to backpedal in an attempt to free things up. The chain slack that resulted allowed the chain itself to be sucked into the rear wheel, thereby destroying not only the chain, but also the rear derailleur hanger and probably the derailleur as well. The wheel and even the frame are also damaged, and may not be salvageable.

Yikes.

Headset Shenanigans

I didn't think of taking a picture of this at the time, but an experience I had in the shop today was certainly blogworthy.

A fellow came in with some major stickiness in the Campagnolo "Hiddenset" headset on his Bianchi road bike, which he bought used. After removing the fork to take a look, I found that the top bearings were completely non functioning. Removing the parts from the headset cup, I discovered that there was a grand total of ZERO ball bearings inside. The bearing race was just sitting in the headset cup, as well as an unrelated fork crown race thrown in to take up enough space to fit the top bearing cover back on and make the bike look normal. This was an extremely dangerous condition. Installing the appropriate ball bearings and steerer tube compression ring, as well as removing the extraneous crown race got him back on the road. He will still need to get to a Bianchi dealer to have the headset replaced, as it has been subjected to some pitting.

Did you get your bike used? Have it checked out by a professional mechanic!

Galvanic Corrosion

Aluminum is generally considered a "corrosion-proof" material for building bicycle frames, and it certainly resists corrosion in the sense that it does not rust like steel does. What is common with aluminum frames, however, is the process of galvanic corrosion. The problem with aluminum frames is that the frame is often in contact with a dissimilar metal, such as steel or even different aluminum alloys. The two metals have two different electric potentials, with the possibility of a tiny electrical current flowing between them. The presence of water and an electrolyte (both of which are found in the rider's sweat) facilitates this current flow, and ions begin to flow between the metals. The problem lies in the fact that the metal which loses ions begins to corrode much more quickly that it otherwise would.

Below are two examples of galvanic corrosion occuring on the same frame. The first photo shows a steel ferrule that has been in contact with the aluminum frame for a very long period of time, and has also been exposed to a lot of sweat. The steel ferrule has corroded and gotten stuck in the frame. Luckily, this is an example where the frame has not been affected, only the ferrule.















The second photo shows an area of the frame that has been in contact with another aluminum part, and also has been exposed to the rider's sweat for some time. In this example, the frame is the part that has been corroded by the process. You can see that the edge of the cable exit hole in the frame has begun to be eaten away. The other part involved is not pictured, but has not been affected.

















The solution to the problem of galvanic corrosion lies partly in proper preparation of the parts before assembly, and partly in rider maintenance. A layer of grease between to dissimilar metals will act as an insulator, and is very effective at preventing the problem. However, it is not a substitute for regular cleaning of the bike. This is especially true in the off season when the bike is on a trainer. Because the rider does not have wind current to aid in evaporation of sweat, more of it ends up in contact with the bike. This makes it especially important to try to keep the bike covered when riding on a trainer (we can get you the Safe-T-Net from Minoura or other similar models) and one must remember to clean the bike after workouts. Replacement of cables and housing once a year will also ensure that the insulating layer of grease between parts is there to insulate the two parts.