: the stroke in the cycle of an internal-combustion engine in which the gases are compressed before firing.

Answer Expert Verified The Exhaust stroke. The exhaust stroke is the final stroke of the four-stroke cycle engine. It occurs when the stroke valve is open and the intake valve is closed as can be seen in the picture above.

An internal-combustion engine goes through four strokes: intake, compression, combustion (power), and exhaust. As the piston moves during each stroke, it turns the crankshaft.

At the end of the intake stroke, the piston is located at the far left and begins to move back towards the right. The cylinder and combustion chamber are full of the low pressure fuel/air mixture and, as the piston begins to move to the right, the intake valve closes.

1:fuel injection, 2:ignition, 3:expansion(work is done), 4:exhaust. While there are many kinds of internal combustion engines the four-stroke piston engine (Figure 2) is one of the most common.

exhaust stroke

What Outboard Compression Test Results Mean. Results vary depending on whether the outboard is a Four-Stroke or a Two-Stroke. Good results for Four-Strokes should be 180-210 PSI, and Two-Strokes should be around 110-130 PSI.

As a result, the combustible mixture of fuel and air fills the chamber. Compression stroke: at the end of the intake stroke, both inlet and exhaust valves are closed. The inertial action of the crankshaft in turn lifts the piston which compresses the mixture.

Yes. Valves will be closed at TDC after the compression stroke and partially open (exhaust closing and intake opening) at TDC following the exhaust stroke.

Once the top dead center timing mark is lined up with the marker on the engine, the motor should now be at top dead center. To verify, shine the flashlight down into the spark plug hole. You should be able to see the top of the piston clearly near the top of the cylinder.

At this point there are a few ways to confirm the compression stroke:

1. Vacuum Pressure Gauge. Use a vacuum/pressure gauge. Hook up the gauge to your hose. Again turn the engine over by hand until you see pressure.
2. Keep going until you see the pressure change to vacuum. Move on to STEP FOUR.

Rotate the engine CLOCKWISE and watch the #1 intake rocker. When it opens and then closes, you are about 180 degrees from TDC on the crank. Turn the engine some more until the notch on the pulley lines up with the seam in the case. You are at TDC now.

to set your base timing without a light, you just turn the motor over in it’s normal direction of rotation until the mark lines up with where you want it.. loosen up the distributor and hook up a spare spark plug to the #1 plug wire.. turn the distributor until it sparks.. tighten down the distributor..

Symptoms of a Bad or Failing Timing Belt

• You Hear A Ticking Noise Coming From The Engine.
• Your Car’s Engine Won’t Turn Over.
• You Notice An Oil Leak Near The Motor.
• You Experience Exhaust Issues.
• Your Revs Start Acting Up.

How to Set the Ignition Timing With No Timing Marks

1. Mark the spark plug wires for the cylinder number using a short piece of masking tape on each wire.
2. Rotate the engine clockwise and observe the valves on the number one cylinder.
3. Locate the number one spark plug wire on distributor cap and make a tic-mark of this position with a marker pen on the distributor housing.

If ignition timing is too far advanced, it will cause the fuel-and-air mixture to ignite too early in the combustion cycle. This can cause the amount of heat generated by the combustion process to increase and lead to overheating of the engine.

Stroboscope

That is typically 15-35 degrees before TDC (top dead center) of the power stroke depending on the engine speed. Best power is achieved when ignition timing is set to fire the spark ahead of time to reach that peak pressure at about 2 degrees after TDC.

In addition, the WSM says spark advance should be between 6 to 18 degrees BTDC at idle.

Advance timing, and response increases, easier to start, more power(torque) off idle. Some engines use the vacuum advance to advance timing at idle.

Symptoms of incorrect ignition timing are poor fuel economy, sluggish acceleration, hard starting, backfiring, or “pinging” or “spark knock”. Too little spark advance will cause low power, bad gas mileage, backfiring, and poor performance. Too much advance will cause hard starting and pre-ignition.

as was brought out, the timing has little effect on rich/lean issues and even less on a computer controlled engine.

Rev the engine past the point where your mechanical advance is fully engaged. (Usually, 3,000 – 3,500 rpm will do it.) Watch the timing mark on the harmonic balancer using the timing light. Rotate the distributor until the timing mark lines up at zero with the light.

There is no such thing as too much ignition timing. The terminology for petrol engines with spark plugs is degrees before top dead centre, or degrees after top dead centre. So the question comes down to – too much retardation, or too much advance. Retarded ignition would not enable the engine to achieve maximum rpm.

The timing can vary between 2 and 12 degrees BTDC, the recommended spark plugs are different and even the plug gaps vary. In most cases starting out with 12 degrees of initial advance is about right.