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Gear Case
A chainguard that totally encloses the chain, usually found only on roadsters. Gear cases (also known as "chain cases") are extremely practical for utility bicycles. They keep the chain clean in all weather, and permit cycling in ordinary street clothes without risk of soiling. Unfortunately, a satisfactory chain case to work with derailer gears has not been developed, so they are only found on one-speed bikes or those with internal-gear hubs. Sometimes referred to as an "oil bath", though most of them are not tight enough to act as an actual "oil bath." An exception is older Sunbeam models, where there was actually a pool of oil contained in the bottom of the gear case.
Chain replacement with a gear case:
- You will need to remove the disc that covers the chainwheel. Pry it with a flat-blade screwdriver, as with the lid of a paint can.
- Remove the pieces at the back by undoing the obvious screws. That's as far apart as it needs to come for chain replacement.
It's very helpful if you have a proper workstand that lets you tilt the bike up and down, but if you don't, a strong friend can handle the bike for you. - Set the bike vertical with the front end downward, and drop one end of the chain into the upper section of the chain case until you can thread the end of the chain onto the chainring.
- Once the end of the chain has engaged the chainring, pivot the bike vertically so that it's facing straight up. Turn the cranks forward to feed the end of the chain through the lower run of the chain case until the end appears at the rear opening.
- Join the chain, either with the master link or with a chain tool, and put it all back together.
(To actually remove the chain case, you need to remove the right crank. There's a bolt hidden behind the chainwheel, screwed into a special fitting on the chainstay.)
