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Valve & Cam Timing

Valve Timing Subaru Robin EX21 & KX21 Engines

Understanding valve timing a simple explanation
When it comes to setting the valve timing on an ex21 or kx21 it is a simple job that does not require any special tools.
Valve timing is a very important part of any engine, it opens & closes the valves in relation to the crankshaft & piston position & also gets the ignition coil to fire at the correct time. All these elements rely on the crankshaft that has the flywheel with its magnet to fire the coil as it passes the coil out riggers, the journal on the crankshaft has the conrod or “connecting rod” as it attaches the piston to the crankshaft. On the outside of the crankshaft on the opposite side to the flywheel is the crankshaft timing cog. The timing cog in a chain driven or over head camshaft engine is stepped down so the camshaft turns at half the crankshaft speed so the valves can operate through the 4 cycles of a 4 stroke engine.
If camshaft timing is not set correctly & the piston is pushed up the bore & the valve doesn’t close in time the valve will hit the top or crown of the piston bending the valve or embedding the head of the valve into the piston.
The Subaru camshafts have 2 distinctive lines on the toothed gear on the opposite side of the flywheel side of the gear. The 2 lines need to be aligned with the cylinder head rails that the rocker cover gasket sits on
The 2 marks on the cam need to line up with the head, the camera angle makes them look slightly of set
The triangular shape points to the foot of the engine block, this needs to line up with the mark on the crankshaft gear that is on the bottom side of the crank. If you put the crank gear marker and align it directly with the mark on the block the timing will be 180 degrees out & valves will bend..
The timing mark on the crank gear faces the foot or bottom of the engine block and lines up with the triangle on the engine block.
When setting the valve timing the 2 lines on the cam line up with the cylinder head rocker cover gasket flat,the timing mark on the crankshaft is closest to the opposite end of the cylinder head at around 8.00 oclock & the key way for the clutch side of the crank is sitting at around 12 oclock
Valve & rocker clearance
rocker clearance, tappet clearance, rocker gap, valve lash are 4 different names that all describe the same thing. As an engine runs & goes through its cycle the valves open many times, the rpm does not change the distance that the valve opens but the higher the rpm the more times the valves are opened & closed with the valve springs being compressed. When an engine runs it produces energy that also turns into heat & as we all know heat causes things to expand.
The rocker clearance is what we will call it is set with the valves closed with the rocker arms on the back of the camshaft this is the where the camshaft is not pushing open the valves. You will need a set of feeler gauges to measure the gap between the tip of the rocker where it makes contact with the top of the valve then with the lock nut loosened adjust the threaded tip that runs through the rocker arm to give the correct rocker clearance 0.15mm. As the engine heats up the rocker gear expands and the gap reduces if we started with a gap of zero or + 0.50mm or + 1.00mm as the engine heats up the valve would not fully touch the seat & the valve would remain slightly open.
The feeler gauge is placed between the adjuster screw & the valve tip. The screw is wound in or out then once the feeler gauges slide in & out at the desired clearance the screw is held in position and the lock nut is tightened. Once it is locked up recheck it again.
The Way to set the cam timing is the same from EX13, EX17, EX21, KX21 & EX27 engines