How to Check Crankshaft End Play or Thrust Using a Magnetic Deck Bridge: Engine Building 101

Summary

In this video, Brian from Summit Racing demonstrates how to check the crankshaft thrust and ground play during an engine build. He emphasizes the importance of proper thrust measurement to prevent damage caused by excessive forward force from the transmission, especially in high-performance engines. The video explains different methods of checking thrust, highlighting the advantages of using a bridge indicator for accuracy. Brian walks through the steps, from positioning the crank to adjusting the thrust bearing, ensuring optimal crankshaft movement for a successful engine assembly.

Takeaways

• 😀 Checking crankshaft thrust and ground play is crucial during engine assembly.
• 😀 Transmissions can create significant forward force on the crankshaft, especially in high-performance applications.
• 😀 Excessive end play in the crankshaft can lead to engine damage and teardown.
• 😀 It's important to check crankshaft thrust during the assembly process to prevent future issues.
• 😀 Magnetic base indicators are commonly used to measure crankshaft thrust but may not always be precise due to flex in the arm.
• 😀 A bridge indicator is a more solid and repeatable tool for measuring crankshaft thrust.
• 😀 Ensure the bridge indicator is properly zeroed before beginning the measurement process.
• 😀 When checking for thrust, rotate the engine and apply force to measure the lateral movement of the crankshaft.
• 😀 Double-check the positioning of the indicator to avoid interference with the crank flange bolt holes.
• 😀 Ideal thrust clearance should be between 5 thousandths to 7 thousandths and two tenths.
• 😀 If the thrust clearance is too small, the main caps should be disassembled, the crankshaft pulled out, and the thrust bearing polished to adjust the clearance.

Q & A

Why is it important to check the crankshaft thrust and ground play during engine building?

Checking crankshaft thrust and ground play is crucial to prevent excessive lateral movement, which could lead to engine damage or the need for a costly tear down, especially in high-performance applications where transmissions can create significant forward force.

What tools are typically used to check crankshaft thrust during engine assembly?

Two common tools used for checking crankshaft thrust are a magnetic base indicator and a bridge indicator. The bridge indicator is often preferred because it provides more stability and repeatability during measurements compared to the magnetic base with an arm.

What is the main issue with using a magnetic base indicator for this measurement?

The issue with using a magnetic base indicator is that the arm can introduce flex and movement, making the measurement less repeatable and reliable.

What is the advantage of using a bridge indicator to check crankshaft thrust?

A bridge indicator is more stable and repeatable because it is solid, magnetic, and can be easily mounted directly to the back of the cap for accurate measurements.

How should you position the indicator to avoid errors during measurement?

The indicator should be positioned between the bolt holes on the back of the crank flange to prevent it from falling inside the bolt holes, which could interfere with accurate measurements.

What is the typical range of crankshaft thrust movement needed for high-performance engines?

For high-performance applications, the ideal range of crankshaft thrust movement is typically between 5 thousandths to 7 thousandths and two tenths of an inch.

What happens if the crankshaft thrust measurement is too low?

If the crankshaft thrust measurement is too low, there may not be enough lateral movement to accommodate the forces exerted on the crankshaft, which could result in engine damage or premature wear.

What should be done if the thrust measurement is insufficient?

If the thrust measurement is insufficient, the engine builder should disassemble the main caps, remove the crankshaft, take out the thrust bearing, and polish the thrust bearing to allow for more back-and-forth movement and achieve the desired thrust measurement.

How much thrust movement was observed in the video, and was it sufficient?

The video shows only about 2 thousandths and eight tenths of an inch of thrust movement, which was deemed insufficient for the high-performance application. The ideal range was specified as being 5 to 7 thousandths.

What is the purpose of zeroing out the indicator during the measurement process?

Zeroing out the indicator ensures accurate measurements by setting a reference point before applying any force on the crankshaft, allowing for precise readings of the thrust movement.