Automotive Intake, Exhaust, and Cylinder Head Maintenance

Intake Manifold Functions

The intake manifold directs inlet gas to the cylinders.

• Otto Carburetor and Single Point: The mixture is created collectively and injected through the throttle body, then distributed to each cylinder. Optimal distribution requires tubes that are as short, straight, and equal in length as possible. A common method involves passing cooling fluid through a duct located in the collector after the throttle butterfly. Warming the mixture increases its volume, which can negatively impact cylinder filling.
• Multipoint Fuel Injection: Fuel is dosed individually for each cylinder and injected at the inlet valve, allowing for better cylinder filling. Variable intake systems adapt the size of the ducts as engine revolutions increase.

Exhaust System

The exhaust system collects combustion gases leaving the exhaust valves at high velocity and high temperature, leading them to the muffler. Dimensions are calculated to facilitate efficient gas exit.

4. Checking the Cylinder Head

• Thread Inspection: Check all threads, including studs, screws, and drill holes.
• Head Gasket Surface: The maximum allowable deformation is 0.05 mm; if it exceeds this, the surface must be rectified. Verification is performed using a feeler gauge and a straightedge (longitudinal, transverse, and diagonal) or by using a surface plate.
• Collector Supports: Check support levels to ensure no more than 0.1 mm of deformation.

5. Grinding of the Cylinder Head

This process is performed in workshops using precision tools.

Implications

• Decreases the volume of the combustion chambers and increases the compression ratio, which raises the temperature in the chamber and creates a risk of detonation.
• Some manufacturers provide gaskets with additional thickness to compensate for grinding.
• Valve Seats: Lower the valve seat to the same extent as the grinding to avoid collisions with the piston.
• Diesel Engines: Measure the distance from the pre-chambers and, after grinding, ensure they remain the same by adding washers.
• Parallelism: Check the longitudinal parallelism by measuring the height at both ends (must not exceed 0.1 mm).

Measuring Combustion Chamber Volume

Mount the valves and the spark plug, then place the cylinder head with the chambers facing up horizontally. Place a piece with an orifice over the chamber, use a graduated cylinder with fluid (oil), and pour it into the chamber until full, ensuring no bubbles remain.

• Tolerance: The volume tolerance is +/- 0.6 cm³. Measure and compare all volumes; the maximum difference should be 1 cm³. This identifies variations between chamber volumes, though it does not determine the total compression ratio, as that also depends on the block volume.

Computation of Combustion Chamber Volume

Knowing the compression ratio (Rc) and the swept volume (Vu):

Vc = Vu / (Rc - 1)