Chapter 58 PowerPoint

Define these Technical Terms using the textbook:

1. camshaft bearing clearance

2. camshaft end play

3. camshaft lobe wear

4. head warpage

5. three-angle valve job

6. valve grinding

7. valve spring free height

8. valve spring shims

9. valve spring tension

Answer these discussion questions using the textbook:

1. What happens when valve stem seals are bad?

Read the chapter summary below:

■ Cylinder heads can suffer from a wide range of problems, including warpage, cracks, burned seats, burned valves, and worn valve guides.

■ Head warpage is checked with a straight edge and feeler gauge. Check at different angles across the head.

■ Milling is used to correct head warpage.

■ A cracked cylinder head can be welded, plugged, or replaced.

■ Excess valve guide wear allows the valve stem to move sideways in its guide during operation, which can lead to oil consumption, a light knocking or tapping sound, burned valves, or valve breakage.

■ Valve guide wear can be checked with a dial indicator or a small hole gauge and micrometer.

■ Valve guide wear can be corrected by knurling, reaming oversize, installing a new guide insert, or installing a bronze guide liner.

■ Valve seat reconditioning involves grinding or cutting a new face on the seat. Valve seats can be resurfaced with a grinding stone or carbide cutter. The grinding stone must have the correct angle, which is usually 45°, but sometimes 30°.

■ Valve seat replacement is commonly done by a machine shop.

■ Valve lapping compound can be used to check seat location on the valve.

■ Valve springs should be tested to make sure they can be reused. Check spring squareness, spring tension, and spring free length.

■ Valve spring shims are used to maintain the correct spring tension when the spring is installed on the cylinder head.

■ A valve spring tester is used to determine the needed shim thickness if the spring pressure is lower than specifications.

■ When a valve spring binds, it will no longer compress. Spring bind can be caused by too much shim thickness under a spring, too much valve lift, incorrect rocker arm ratio, or use of incorrect springs.

■ Umbrella seals simply slide onto the valve stems before spring installation.

■ Placing a liquid in the cylinder head ports is a good way to double-check for valve leakage after head reconditioning.

■ When shop air pressure is blown into a cylinder, the valves will stick in the closed position. This will allow for seal and valve spring replacement, without the need to remove cylinder heads from the cylinder block.

■ Camshaft service involves measuring camshaft lobe and journal wear. It also includes measuring camshaft end play and camshaft bearing clearance.

■ Camshaft bearings in the cylinder head of an OHC engine are serviced in much the same way as the camshaft bearings in cam-in-block engines. Check bearings for wear, damage, and clearance. Check camshaft bearing wear by measuring the bearing’s inside diameter.

■ Rocker assembly service involves cleaning, inspection, and measurement of the rocker arms, rocker arm shafts, and related components.

■ You can usually check pushrod straightness by rolling the pushrods on a smooth, flat work surface. Replace any bent pushrod.