Vacuum
Pressure which is less than atmospheric pressure. In terms of a motorcycle engine it is the difference in air pressure between the engine’s intake manifold and Earth’s atmosphere. As the piston travels downwards on its stroke it creates a low pressure void that will be filled by the incoming air/fuel mixture. CV type carburetors also use vacuum to raise the slide at larger throttle openings.
V-twin Engine
An engine configuration with two cylinders arranged in a V instead of inline. The angle between the cylinders is commonly 45 degrees, 60 degrees or 90 degrees, although a 90 degree angle technically speaking should be called an L-twin engine, but we won’t say anything if you tell people that your Ducati has a 90 degree V-twin engine.
Truing
Can refer to the process of adjusting a crankshaft so that it spins within specification. More often the term is used to refer to the painstaking process of adjusting a spoked wheel to correct any irregularities in lateral and radial runout, also known as wobble and hop. This is done by tightening and/or loosening spoke nipples until the runout readings are within specification.
Tightening Sequence
Upon both disassembly and re-assembly of various motorcycle components, most notably motorcycle engines, there is predetermined numerical or pattern sequence in which bolts should be removed or tightened. Failure to follow this sequence can result in component damage, specifically, warping or cracking the component. In the case of a cylinder head, the manufacturer often recommends following a criss-cross pattern in addition to a series of tightening stages. As a general rule of thumb, tighten larger diameter fasteners first and then the smaller ones.
Slide Cutaway
The slide cutaway refers to the carburetor circuit which controls the air/fuel ratio from one-eighth to one-quarter throttle opening on slide type carburetors. The height of the cutaway portion of the carburetor slide controls how much air is mixed with fuel, the larger the slide cutaway number the leaner the transition off of idle will be.
Preload
In terms of motorcycle and ATV suspensions, spring preload is the static length of a spring (as it is installed in a motorcycle fork or shock) subtracted from its free length (as it is uninstalled). The spring preload determines the motorcycle ride height and sag. In motorcycle forks, preload is adjusted by the use of fork spacers installed in the fork tube or by turning a preload adjuster. On motorcycle shock absorbers, spring preload is adjusted by turning an adjusting ring that is secured by a lock ring or by turning a cam ramp. Adjusting preload is an important part of achieving proper suspension sag.
Rear Sprocket
The sprocket or toothed gear that drives the rear wheel(s) of a motorcycle or ATV. Sprockets are bolted to the hubs of motorcycle wheels and bolted to the axles of ATVs and are turned by the drive chain.
Rake
In motorcycling, rake refers to the angle of the forks from a true vertical position. Rake is measured counterclockwise from true vertical when viewed from the right side. A 0° rake would be considered vertical. Choppers are often referred to as being “raked-out” because their forks are fixed at a more forward angle. Some states have requirements as to the minimum and maximum rake a motorcycle is permitted to have for safe operation. Rake effects both the stability of the vehicle and steering “quickness”.
The 1997 Kawasaki ZX-6R has a rake of 24° as an example.
Ohmmeter
The setting of a multimeter that allows you to test the resistance of a component, measured in Ohms of resistance. Motorcycle Service Manuals usually give specifications for the resistance of some of the electrical components found on the vehicle.
Ammeter
An instrument for measuring amperage (current flow) in electrical circuits.
