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Bearing cups are pressed into the bottom bracket shell. The crank holds the cones, facing in; adjustment is made via the left-threaded non-drive side cone. One-piece cranks are easily maintained and reliable, but heavy. They are found on BMX bikes as well as children's bicycles and low-end road and mountain bikes.
The cranks are pressed into place and prevented from squirming off via fretting by a bolt or nut installed into or onto the bottom bracket spindle. [8] The head of the bolt or the nut sits inside a counterbore that is also threaded to accept a crank puller tool. The counterbore is often covered with a dust cover.
When describing a crankshaft design, the number of main bearings is generally quoted, as the number of crank pins is determined by the cylinder layout. For example, the Toyota VZ V6 engine is described as having a "four bearing crankshaft" and the Jaguar XK6 straight-six engine has a "seven bearing crankshaft". [2] [3]
[15] [1]: 126 The engines were a complete redesign, with the crankshaft bearings upgraded from roller bearings to shell-type journal bearings (the type used in modern car engines). [ 15 ] [ 1 ] : 126 The camshaft was now chain-driven and located underneath the crankshaft instead of at the top of the engine, in order to lower the centre of ...
The crank bearings require periodic maintenance, which involves removing, cleaning and repacking with the correct grease. The chain and the brake blocks are the components which wear out most quickly, so these need to be checked from time to time, typically every 500 miles (800 km) or so.
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A tunnel crankcase, tunnel crankshaft or disc-webbed crankshaft [1] is a design feature of a piston engine where the main bearings that support the crankshaft within the crankcase form the largest diameter of any part of the crankshaft and are larger than the crank webs. This requires a crankcase with a large tunnel instead of cross web ...
A second disc is attached to the bottom of the thrust bearing such that the entire assembly moves together up and down the steering axis while each disc can rotate independently around the axis. A second set of cables are attached to tabs on this lower disc and pass through cable stops mounted on the either side of the head tube .