Dual Overhead Camshaft (DOHC): A Comprehensive Technical Guide and DIY Measurements

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Dual Overhead Camshaft (DOHC) engines are a popular design choice for modern high-performance vehicles, offering enhanced valve control and improved engine performance. This comprehensive guide delves into the technical specifications, measurements, and DIY tips to help you understand and work with DOHC engines.

Technical Specifications of DOHC Engines

DOHC engines feature two camshafts located in the cylinder head, with one camshaft dedicated to the intake valves and the other to the exhaust valves. This design provides several key advantages:

  1. Number of Camshafts: DOHC engines have two camshafts, one for the intake valves and one for the exhaust valves.
  2. Camshaft Location: The camshafts are situated in the cylinder head, allowing for precise control over the opening and closing of the intake and exhaust valves.
  3. Valve Control: DOHC engines offer greater control over valve timing and duration, enabling more efficient engine operation and increased performance.
  4. Performance Benefits: The enhanced valve control in DOHC engines can lead to improved engine performance, higher rev limits, and increased horsepower output.

Measuring Camshaft Lift and Duration

dual overhead camshaft

Accurately measuring the camshaft lift and duration is crucial for understanding the performance characteristics of a DOHC engine. Here’s a step-by-step guide on how to perform these measurements:

Camshaft Lift Measurement

  1. Dial Indicator Setup: Secure a dial indicator with a magnetic base to the cylinder head, positioning the indicator’s tip on the top of the valve stem.
  2. Zero Point Determination: Slowly rotate the engine until the camshaft lobe contacts the valve shim, and the dial indicator needle starts moving. This is your zero point for the measurement.
  3. Lift Calculation: Continue rotating the engine and count the number of full rotations the dial indicator needle makes until it changes direction. Each full rotation represents 1 millimeter of lift, and each sub-segment is 0.1 millimeters.
  4. Lift Value: The total number of rotations will give you the camshaft lift value.

Camshaft Duration Measurement

  1. Duration Measurement Point: Most camshaft manufacturers measure duration at 0.05 inches (1.3 millimeters) of lift.
  2. Counting Duration: Start counting the number of degrees the camshaft lobe is in contact with the valve shim, from the point where the lift reaches 0.05 inches until it drops back down to 0.05 inches.
  3. Duration Value: The total number of degrees counted will give you the camshaft duration value.

DIY Tips for Accurate Measurements

To ensure the accuracy of your camshaft lift and duration measurements, consider the following DIY tips:

  1. Tool Rigidity: Ensure that your measurement tools, such as the dial indicator and engine rotation tools, are highly rigid and consistent to minimize any accidental distortions.
  2. Measurement Precision: Even the slightest bit of unintentional touching or movement can affect the accuracy of your measurements, so be extremely careful and precise during the process.
  3. Lift Measurement Simplicity: Measuring camshaft lift is a relatively straightforward process, as it only requires counting the number of rotations of the dial indicator needle.
  4. Duration Measurement Complexity: Measuring camshaft duration is more involved, as it requires stopping the counting at the precise 0.05-inch (1.3-millimeter) lift point to obtain the final duration value.

By following these technical specifications, measurement procedures, and DIY tips, you can gain a deeper understanding of DOHC engines and perform accurate assessments of their performance characteristics.

References

  1. DCAA Incurred Cost Audit Procedures
  2. Camshaft Lift and Duration Measurement Video
  3. Earned Value Management Systems Analysis