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Agnes - Module 3 Training
Transcript of Agnes - Module 3 Training
Compression Release System
EX engines employ an automatic decompression system as a standard feature. This enables easy starting of the engines, with lighter recoil pull.
The automatic decompression system releases the compression of the engine by lifting up the exhaust valve at cranking speed.
Valve clearance is critical on EX engines for good performance and easy starting.
The ignition system is a transistor controlled magneto system with the ignition timing set at 23 degrees (EX13/17/21) and 27 degrees (EX27) before the top dead center. The magneto consists of a flywheel and ignition coil. The flywheel (which also works as a fan) is directly mounted on the crankshaft and the ignition coil is directly mounted on the crankcase.
Here's a video how to install timing chain
At the end of the compression process, the release lever lifts up the rocker arm (exhaust) which in turn opens up the exhaust valve slightly to release the compression.
The release lever has a flyweight on its end and another end of the lever is a crescent cam. When the engine is cranked, the crescent cam projects above the cam profile and lifts up the rocker arm (exhaust) because the force of the return spring on the weight is larger than the centrifugal force on the weight.
When the cranking speed reaches a specified r.p.m., the crescent cam is retraced under the cam profile because the centrifugal force applied to the flyweight becomes larger than the force of the return spring on the weight and thus it is shifted to the position shown in the illustration below.
Adjusting Valve Clearance video
The oil sensor is composed of the float and permanent magnet incorporated into the float and the oil sensor. In accordance with the oil level, the float moves up and down. When the oil level is high, the float moves up.
When the oil level is low, the float moves down. The permanent magnet is close to the lead switch, and the lead switch is activated by the magnetic force.
Timing chain links the movement of the piston and cylinder to the opening of the intake and exhaust valves. It also acts as a conveyor to carry oil from crankcase to the cylinder head of the engine.
The timing chain connects the sprocket portion.
The sprocket teeth are designed for maximum durability and low noise.
Understand how the timing chain operates and provides precise opening of the engine intake exhaust valves in relation to piston
Understand how oil sensors and related components work
Understand major components and theory of operation of ignition system
Understand how to check compression on EX engine
Know how to replace recoil rope
Know know to check and adjust valve clearance
Checking and Servicing Component Systems of the EX Engine
There are two styles of oil sensors.
Major components are float switch and control module. Control module is either in the switch or it's separate.
Low oil shutdown is connected to the on/off switch.
Chain guide has different mounting positions depending which engine it's used on.
-should be parallel to top surface of the cylinder head when engine is top dead center
Check air gap between flywheel magnet and ignition coil with non magnetic fuel gauge.