A flywheel plays a vital role in your vehicle’s drivetrain, absorbing and dissipating heat generated by the clutch. Over time, this can lead to wear and tear, necessitating a thorough Flywheel Inspection, especially during clutch replacement. This article will guide you through the process of inspecting a flywheel and discuss resurfacing techniques.
Why Flywheel Inspection Matters
Clutch operation generates significant friction and heat, which the flywheel absorbs. Excessive heat from a slipping clutch can cause cracks, warping, and hard spots on the flywheel surface. These imperfections can lead to clutch chatter, vibration, premature wear, and even clutch failure. A comprehensive flywheel inspection ensures a smooth and reliable clutch operation after replacement.
Conducting a Flywheel Inspection
When the old clutch is removed, carefully inspect the flywheel for:
- Runout: Measure the flywheel’s flatness using a straightedge and feeler gauge. Even slight deviations from flatness (more than .002 inches) can cause issues. Excessive runout (over .005 inches) significantly increases the risk of damaging vibrations.
- Cracks: Examine the flywheel surface for any cracks, paying close attention to areas around the crankshaft bolt holes. Deep or extensive cracks warrant flywheel replacement due to the risk of catastrophic failure.
- Grooving and Hard Spots: Look for any signs of grooving or discolored, raised areas (hard spots) on the flywheel surface. These indicate wear and necessitate resurfacing.
- Starter Ring Gear: If the starter ring gear is a separate component, inspect its teeth for damage. Damaged teeth can hinder engine cranking and should be replaced.
Flywheel Resurfacing: Grinding vs. Cutting
If the flywheel inspection reveals imperfections, resurfacing is necessary. Two primary methods exist:
- Cutting: This method, often performed on a brake lathe, can be time-consuming and requires precise setup. Lathe bits may skip over hard spots, resulting in an uneven surface. Excessive metal removal can also affect clutch height and engagement.
- Grinding: Generally preferred, grinding utilizes a dedicated flywheel grinder or a head and block grinding machine. Grinding effectively removes hard spots and produces a smooth surface with minimal metal removal. Dedicated flywheel grinders offer faster setup and accommodate various flywheel designs, including stepped or recessed flywheels.
Dual-Mass Flywheels: Special Considerations
Dual-mass flywheels (DMFs) require different approaches:
- BMW, GM, and Porsche: Resurfacing is not recommended; replacement is necessary if worn.
- Ford: DMFs can be resurfaced by separating the primary and secondary flywheels. New bolts are recommended during reassembly.
- Solid Flywheel Conversions: Some applications allow replacing DMFs with conventional solid flywheels. While potentially more affordable and reliable, solid flywheels may sacrifice smoothness and vibration dampening.
Flywheel Resurfacing Best Practices
- Maintain Clutch Height: When resurfacing stepped flywheels, remove equal amounts of metal from all surfaces to preserve proper clutch height and pressure.
- Achieve Proper Surface Finish: Use appropriate grinding stones (silicone carbide for wet grinding or CBN for dry grinding) and coolant for optimal results. Softer stones are suitable for forged steel, while harder stones work best on cast iron.
- Address Radius on Recessed Flywheels: Remove any radius left by grinding on the corners of recessed flywheels to ensure proper clutch pressure plate contact.
Flywheel and Clutch Replacement Tips
- Replace as a System: When replacing a clutch, replace all related components, including the clutch disc, pressure plate, release bearing, and pilot bearing or bushing.
- Maintain Engine Balance: When replacing a flywheel on an externally balanced engine, mark its index position before removal to ensure proper reinstallation and maintain engine balance.
Conclusion
Flywheel inspection is crucial for ensuring a successful clutch replacement and preventing future problems. By understanding the inspection process, resurfacing techniques, and specific considerations for different flywheel types, you can contribute to a smooth, reliable, and long-lasting clutch system. Always consult your vehicle’s service manual for specific instructions and torque specifications.
