Compression release is a device used in combustion engines to make starting easier by bleeding built-up compression or pressure from the cylinders. It is commonly found in motorcycles, snowmobiles, and other small engines and can be activated by a lever or small button switch. Malfunctions can be easily fixed by a home mechanic.
A compression release is a device used in combustion engines to allow easier starting. As the piston moves up in the cylinder, it builds pressure known as compression. This pressure can make cranking the engine nearly impossible. Compression release allows the operator to bleed built-up compression or pressure from the cylinders, making the engine very easy to crank and start. When starting the engine, the compression release re-engages and the engine again builds the compression required to allow it to run and produce power.
A compression release is most common on motorcycles, snowmobiles, and other small engines that are usually started by kicking them with a starter or pulling them with a rope. On some very high compression engines, such as the larger V-twin designs, a compression release with an electric starter is also used to avoid burning out the starter while trying to crank the large engine. This same system is also found on some very large diesel engines. Some of the smaller two-stroke engine machines, such as chainsaws and outboard motors, also use a compression release to aid the starting process.
The typical compression release device is activated by a lever much like a manual choke switch. Other types are released simply by pressing a small button-type switch on the cylinder head of the engine. In either case, once compression release has kicked in, it allows the engine to easily come on for a rev or two before compression begins to build again. If the engine does not start on the first attempt, the compression should be released one more time before another attempt is made to start the engine. Once the engine starts, there is no need for the operator to take any further action.
Occasionally the small device will malfunction and require replacement. This is usually a minor operation and can often be easily accomplished by the home mechanic with simple hand tools. On some engines, including diesels, the repair is more extensive and is best done by a licensed mechanic. Typical compression release requires no specialized maintenance or lubrication and is relatively trouble free in most cases. Occasionally a manufacturer will recommend the addition of an engine oil treatment additive on top to keep the device seals lubricated and eliminate any troublesome sticking that will sometimes affect the release device.
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