CYLINDER HEAD

The cylinder head from an L-head engine dose not require major disassembly. Therefore the disassembly portion of this study unit refers mostly to the I-head and F-head engines. The cylinder head is cleaned and inspected just as the engine block was; therefore, it is unnecessary to go into a detailed description. Let's get right to inspection and the repair of the cylinder head.

1. Cylinder Head Inspection and Repair

Begin disassembly by removing the valves. With a valve spring compressing tool compress the valve spring and remove the valve stem locks. There are various types of valve spring compressors. The one described is one of the more common. The spring is compressed by placing the solid end of the compressing tool on the valve head and

the split end of the spring retainer, then compress it with the lever located on the tool. Once this is accomplished, you can easily remove the valve stem locks with your fingers. Cup

your hand over the end of the spring now and release the lever. The valve spring and its related parts are then removed by hand. The valve may also be removed from the bottom side of the cylinder head by hand. Keeping each valve and its related components together, lay them out on a clean surface and carefully inspect each piece for damage.

Valves and related parts.

Now, remove the coolant outlet connection and check the thermostat operation. To remove the outlet connection, simply remove the cap screws retaining it and lift it from the head. Remove the thermostat and drop it into boiling water to check its operation. The thermostat should open. Remove the expansion plugs and replace them as you did in the engine block. Check the head for nicks, burrs, and cracks. Smooth any nicks and burrs with oil stone. A cracked head may be sealed in some cases. The cylinder head is now ready for specification checks. The flatness check is performed to ensure that the head is not warped. This check is made in the same manner as the cylinder head gasket surface of the cylinder block. A straight edge and a feeler gage are used to determine the amount of warpage. Figure below is a good illustration of how to perform the checks.

Checking cylinder head flatness.

Figure shows where these checks should be made. The lines drawn across the surface indicate the positions in which the straight edge should be placed for checking. If you were

working on a cylinder head from an L-head engine, this is the only check you would be required

to make.

Positions for checking cylinder head for flatness.

If the results of the check reveal that the cylinder head warpage exceeds the tolerances listed in the TM, you must have the head ground to obtain a new, flat surface. In some cases, the head may have already been ground as far as allowed and in other cases, heads are manufactured in such a design that they cannot be ground at all. In these cases, discard the cylinder head and obtain a new one through the supply system.

2. Valve Seat Inspection and Repair

Your first step would be a visual inspection. It is important that the valve seat be of the proper width to ensure an air-tight seal and proper valve cooling. Although the entire surface of the valve seat is machined smooth, only a small portion of that surface is actually contacted by the valve when it is closed. If the head is equipped with cast in seats, improper fit or damaged seats would need to be ground (refaced). Grinding requires the use of a electric drill motor and grinding stones of various degrees of angle. Consult the appropriate TM for the proper angle.

Grinding valve seats.

Care must be exercised to prevent the grinding of too much metal from the surface of the seat.

Check contact surfaces between the valve and valve seat by applying a light coat of Prussian blue

dye to the valve face. Lower the valve stem into the valve guide and let the valve drop against the

valve seat. Apply pressure valve head until valve face makes good contact with valve seat, BUT

DO NOT ROTATE. Push up on valve stem until valve face is about one inch above valve seat.

Drop valve back into valve seat and reapply pressure to valve head. Repeat this procedure several

times to get a good imprint in the Prussian blue dye. Being careful not to smear the dye, remove

valve. The imprint in Prussian blue dye should have an even seat mark all the way around the

center of the valve face. If the head you are working on has replaceable seats (valve seat inserts), badly damaged seats

must be replaced. Remove and replace valve seat inserts as illustrated in figure A and B.

A. Removal of valve seat inserts. B. Replacement of valve set inserts.

After valve seats have been replaced, perform a runout check. The valve seat runout check ensures that the seat is perfectly round. This is accomplished by the use of a dial indicator type gage known as a runout gage. The gage manufacturer provides instructions for its use, but basically, you insert the base of the gage into the valve guide, adjust the measuring device to seat on the contact surface of the valve seat, and run the measuring device around the valve seat. The maximum reading reached on the dial indicator tells what the runout is. The runout is then checked against the tolerance listed in the TM.

Checking valve seat runout.

3. Valve Guide Inspection and Repair

Although you may have repaired or replaced the valve seats, the valves will not seat properly unless the valve stem clearance is correct. Check the valve stem clearance now to help ensure proper valve seating. Measure the inside diameter of the valve guide with a telescopic gage and the outside diameter of the valve stem with a micrometer. To obtain valve-to-guide clearance, subtract valve stem diameter from valve guide diameter. Check appropriate TM for proper specifications. If the reading you have obtained is greater than the tolerance, either the valve or the valve guide

must be replaced. Check the condition of both and determine which needs replacement. In some cases, both may have to be replaced. If the cylinder does not have replaceable guides, ream the guide and use an oversized valve. If the engine is equipped with replaceable valve guides and a visual inspection reveals that the valve guide is damaged beyond repair, it must be replaced. To replace the valve guide, the old guide must be driven out of the cylinder head or cylinder block and a new one driven in. This is accomplished by placing the valve guide remover inside the valve guide and drive the guide out through the cylinder head with a ballpeen hammer. When installing valve guides, use the appropriate valve guide installer tool and press.

Position valve guide squarely on guide bore and gently press guide into bore. The installer will position guide to the correct depth.

Installing valve guides.

This should complete the repairs of the cylinder head, or in the case of the L-head engine, the cylinder block. The final component to be repaired is the valve mechanism.