How to Grind Auto Valves

The first step to grinding valves is to remove the heads as this mechanic is doing.

This process involves grinding valve seats and lap valves; the more common procedure is lapping valves. Valves are small, mushroom-shaped, metal parts that lift and descend to control the flow of fuel mist into cylinders of gasoline and diesel engines and the flow of exhaust fumes out of those cylinders. There are always at least two valves per cylinder. The valves must tightly seal into openings called valve seats in the cylinder head. If the valves do not seal tightly, the engine loses the ability to compress the explosion that occurs in cylinders so the engine loses power. Lapping the valves makes them fit into the valve seats more tightly.

Things You'll Need

• Service manual for your vehicle
• Valve spring compressor
• Needle-nose pliers
• Coarse valve lapping compound
• Valve lapping tool
• Rags
• Fine valve lapping compound
• New valve seals
• Replacement valve springs (optional)

Instructions

1. Remove the cylinder head or heads from your automobile following the procedures explained in the service manual for your vehicle.

2. Compress the valve springs for your valves, working one valve and one cylinder at a time using a valve spring compressor and following the instructions in your auto’s service manual. For each valve, remove the valve spring keepers, uncompress the valve spring and remove the valve spring.

3. Remove the valve seal with needle nose pliers then remove the valve. Valve seals are small metal and rubber parts that fit over the stem, or long portion, of each valve.

4. Apply coarse valve lapping compound to the interior of one cup of a valve lapping tool. The compound and tool are often sold together as a valve lapping kit. The tool is a thick stick about 9 inches long with a suction cup on each end. Replace the valve in the head to keep the valve stationary while it is lapped.

5. Put the valve lapping tool cup containing coarse compound over the valve head and gently twirl the cup on the valve until all grinding noise stops. Wipe the valve clean with a rag.

6. Apply fine valve lapping compound to the interior of the unused cup of the valve lapping tool. Put that cup over the valve and gently twirl that cup on the valve until all grinding noise stops. Wipe the valve clean with a rag.

7. Repeat these steps for every valve in your engine. Reassemble the cylinder heads using new valve seals and your old or new valve springs following the procedures and specifications in the service manual for your vehicle.

References

• United States Products: Lapping Valve Seating Surfaces
• Affordable Go Karts: Valve Lapping
• SPDWeb.net: Valve Lapping 101
• Arizona State University: Lapping Valves