The cylinder head reaches the highest temperature of any engine component, often thousands of degrees. Water jackets need to be incorporated into cylinder heads to cool them down so they don't completely distort and burn out the head gaskets. The cast iron and aluminum metals used in cylinder heads continually flex under the high temperatures and pressures, and are allowed to do so within limitations. Sometimes, however, the heat can become so excessive that the heads bulge and warp beyond these limits. When this happens it is necessary to dissemble the engine and measure the specified tolerances.
Things You'll Need
- Tech repair manual
- Owner's repair manual
- Bench vice (if applicable)
- Wood blocks
- Carburetor cleaner
- Wire brush
- Steel straight edge ruler (24-inch)
- Feeler gauges
- Pad and pencil
Refer to your owner's repair manual for the correct procedure to remove the head (or heads) from your vehicle. Use the require tools, and have an assistant help you with the chore of lifting and transporting the head to a flat, clean bench surface. Have a technical repair manual to refer to.
Use a wire brush and carburetor cleaner to completely clean the bottom, sides and top of the head. There should be no carbon in the cylinder head combustion chambers or on the flat part of the mating surface. When you have finished you should have a shiny metal surface.
Place the head with the combustion chamber facing up. Secure it in a wide-jaw vice, or prop the head with wood blocks to keep it stable. Take a new, steel straight edge ruler and place it along the outside edge, from one end of the head to the other. Place a feeler gauge in the gap between the bottom of the ruler and the head surface. Start off with the smallest feeler gauge blade.
Work the feeler gauge along the head until the feeler gauge slides in. Change the blade thickness of the feeler gauge to find the maximum allowable gauge thickness that will enter the gap. Measure up and down the length of the head and record the thickest feeler gauge blade that passed through the gap. Write that number down. Perform the exact same procedure on the other side of the head. Write down the thickest blade measurement that passed under the straight edge.
Place the straight edge along the cross-section of the head, from one corner to the opposite corner. You will do the same with the other corner, which will form an "X" pattern across the head, bisecting it through the middle. Record the thickest blade that passes through one angle. Write the number down. Switch to the other corners and take the same measurement. Write down the thickest blade that passed under the straight edge.
Measure straight across the ends of the cylinder head and record the thickest feeler gauge blade that will pass under the gap. Perform the same measurement on the other side. You should have six measurements. Refer to your tech repair manual for the maximum allowable "out-of-flat" tolerances, which will be measured in thousandths of an inch. Aluminum head tolerances will not be the same as cast iron, so make sure you have the correct type head numbers, as well as the engine configuration.
Compare your numbers to the highest allowable for your engine. For instance, a V-6 engine should not have a higher number than 0.003 inches. Any number exceeding 0.004 inches for a four-cylinder or V-8 head will be beyond specifications. Straight six cylinder heads can have no more than 0.006 inches.
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