How to Repair a Motorcycle's Cylinder Head

Motorcycle cylinder heads are repaired in a machine shop.

Motorcycle heads are made from cast aluminum alloy that house tempered steel components. Other than the engine's pistons, the moving parts in a motorcycle cylinder head are subject to the highest degree of wear. While most heads can be repaired, sometimes it may be more cost-effective to replace the head. Repairing a motorcycle's cylinder head occurs in a motorcycle machine shop. The procedure includes a thorough evaluation, performing the necessary machining and servicing the valves, valve guides and valve springs.

Instructions

1. Remove the valve springs, valve guides, valve seals and valves. Remove any broken studs or bolts.

2. Inspect the cylinder head closely for cracks. Look for scarred valve ports or pitted valve seats. Any of these indicate the need for brazing to fill cracks and pits. In the event brazing is not needed, proceed to the cleaning phase.

3. Steam clean the cylinder head to remove carbon, oil and dirt from all surfaces, crevices and the valve stem ports.

4. Subject the cylinder head to a magna-flux inspection. Magnetic particle inspection is the most effective method of detecting hairline cracks and casting imperfections. Certain imperfections can be corrected by milling or resurfacing the head. Fill surface hairline cracks by brazing. Mill or resurface the head to remove casting imperfections.

5. Mount the cylinder head at a workstation. Hone and polish the valve ports and valve seats. Honing provides precision alignment of valves and valve guides by correcting minor distortions that result from excessive heat.

6. Clean the valves using a fine grinding wheel. Clean hard carbon deposits from the beveled edges of the valves and the valve stems. Remove any carbon deposits from the keeper recesses at the tip of the valve stems.

7. Check the valve springs on a compression tester. The springs must meet or exceed the specified tension. Replace the valve springs, if necessary.

8. Assemble the cylinder head. Insert the valves into the valve ports and install new valve seals and guides. Install the valve springs and retainers. Compress the springs using a spring compressor tool while installing the keepers.

Tips & Warnings

• Cylinder heads vary in design and components. Include overhead cam servicing, if necessary.

References

• Promar: Cylinder Head Repair and Remanufacturing /
• Dan's Motorcycle: Advanced Tools / Cylinder Hone
• Crane Cams: Valve Spring And Retainer Kit / Harley-Davidson