How Much Compression Should a Ryobi String Trimmer Have?
Ryobi string trimmers are powered by an internal combustion, single-piston engine. This type of engine generates compression, which helps get all other systems in the engine moving in one sequence. Without the proper amount of compression, the engine's processes would be restricted or unregulated and inoperable. Does this Spark an idea?
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What is Compression?
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When the piston moves up and down in the cylinder, it drives the crankshaft in the crankcase. As the crankshaft spins, it generates a vacuum pressure, which allows all other engine functions, such as the fuel system, to move with the engine. This up-and-down pulsing helps suck the fuel up into the carburetor and spin the flywheel, which trips the ignition module and fires off the electrical charge necessary for combustion. Compression is the amount of pressure needed to maintain these functions.
How Much Compression
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Compression will rise and fall slightly as the engine works through different speeds and at different operating temperatures. For this reason, an exact compression reading is not a requirement for most engines. When looking for compression and compression loss, it's necessary to see whether the engine maintains compression when necessary, and discharges it when not. Therefore the reading gauges may vary slightly from Ryobi model to Ryobi model. However, as a rule of thumb, a two-cycle engine generally requires 90 psi when hot, and 100 psi when cold.
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Measuring Compression
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A compression gauge, much like a tire gauge, measures the pressure in the engine by reading whether the engine holds air. This gauge connects to the cylinder hole, where the spark plug usually is. Before attaching it, pull the starter rope three to four times to purge the starter and crankcase of air and fuel. Hook the pressure gauge into the cylinder hole and pull on the starter rope until the gauge reaches its maximum pressure. Continue monitoring compression readings and look for sudden and rapid drops in compression readings. Anything under 90 and above 100 psi may be circumspect and require further testing.
Compression Related Problems
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Compression related problems manifest in a wide variety of symptoms, which is why they can be hard to diagnose at first. As the compression issue gets worse, the engine will continue to suffer and eventually die altogether. Compression problems generally occur when an air leak springs along the crankcase seals, piston seals and around the intake manifold. While many problems can be fixed, always weigh the costs of repair against a replacement engine.
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