Inspect the cylinder head components for wear and/or damage.
Inspect the heads of the valves first. Look closely at the head, margin and face for any cracks, excessive wear or burning. The margin is the best place to look for burning. It should have a squared edge with an even width all around the circumference of the valve. When a valve burns, the margin will look melted and the edges will appear rounded. Also inspect the valve head for any signs of tulipping. This will show as a lifting of the edges or dishing in the center of the valve head and will usually not occur to all of the valves. All of the valve heads should look the same. Any valves that seem dished more than others are probably bad. Next, inspect the valve lock grooves and valve tips. Check for any burrs around the lock grooves, especially if they had to be filed to remove the valve. Valve tips should appear flat and square to the valve stem. Slight rounding with high mileage engines is considered normal. Slightly worn valve tips will need to be machined flat. Last, measure the valve stem diameter with the micrometer. Measure the area that rides within the guide, especially towards the tip where most of the wear occurs. Take several measurements along its length and compare them to each other. Wear should be even along the length with little to no taper. If no minimum diameter is given in the specifications, then the stem should not read more than 0.001 in. (0.025mm) below an unworn area of the valve stem. Any valves that fail these inspections should be replaced.
| Valve stems may be rolled on a flat surface to check for bends
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| Use a micrometer to check the valve stem diameter
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Perform a visual inspection for broken springs. Check the free length and squareness of each spring. If applicable, ensure to distinguish between intake and exhaust springs. Use a ruler and/or machinist’s square to measure the length. A machinist’s square should be used to check the springs for squareness. If a spring tension test gauge is available, check each springs rating and compare to the specifications. Valve springs should be replaced as a complete set.
Check the spring retainer-to-spring mating surface and the valve lock retention area for any signs of excessive wear. Check for any signs of cracking. Replace any retainers that are questionable.
Valve locks should be inspected for excessive wear on the outside contact area as well as on the inner notched surface. Any locks which appear worn or broken should be replaced along with its respective valve.
| Spring free-length check
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| Valve spring squareness check
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Check the guides carefully and inspect them for any cracks, chips or breakage. Also if the guide is a removable style (as in most aluminum heads), check them for any looseness or evidence of movement. All of the guides should appear to be at the same height from the spring seat. If any seem lower (or higher) from another, measure the heights to determine if the guide has moved.
Mount a dial indicator onto the spring side of the cylinder head. Lightly oil the valve stem and insert it into the cylinder head. Position the dial indicator against the valve stem near the tip and zero the gauge. Grasp the valve stem and wiggle towards and away from the dial indicator and observe the readings. Mount the dial indicator 90 degrees from the initial point and zero the gauge and again take a reading. Compare the two readings for an out of round condition. Check the readings against the specifications given. An Inside Diameter (I.D.) gauge designed for valve guides will give you an accurate valve guide bore measurement. If the I.D. gauge is used, compare the readings with the specifications. Any guides that fail these inspections should be replaced or machined.
| Reading stem-to-guide clearance
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A slightly worn and pitted surface where the valve face contacts the seat will typically be apparent when valve seats are inspected. Inspect the seat carefully for severe pitting or cracks. A seat that is badly worn will be recessed into the cylinder head. A severely worn or recessed seat may need to be replaced. All cracked seats must be replaced. Use a seat concentricity gauge to check the seat run-out. If run-out exceeds specifications the seat must be machined. If a specification can not be found, use 0.002 in. (0.051mm) as a general rule of thumb for concentricity.
Clean the gasket surface of the cylinder head. Check the head for flatness.
| Machinist’s straight edge and feeler gauge
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| Diagonal check
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Place a machinist’s straight edge across the gasket mating surface. Using feeler gauges, determine the clearance at the center of the machinist’s straight edge and across the cylinder head at several points. Check along the centerline and diagonally on the head surface. If the warpage exceeds 0.003 in. (0.076 mm) within a 6.0 in. (15.2 cm) span, or 0.006 in. (0.152 mm) over the total length of the head, the cylinder head must be resurfaced. After resurfacing the heads of a V-type engine, the intake manifold flange surface should be checked, and if necessary, milled proportionally to allow for the change in its mounting position.
Check the cylinder head for cracks in the spark plug holes, valve ports, exterior surface, or in the valve spring/rocker arm area. Check the exhaust seat/port first as this becomes the hottest area on a cylinder head.
Some reliable methods for finding cracks include Magnaflux®, (a magnetic process) or Zyglo®, (a dye penetrant). Magnaflux® is used only on ferrous metal (cast iron) cylinder heads. Zyglo® is a method that uses a spray on fluorescent mixture along with a black light to reveal the cracks and is suitable for aluminum cylinder heads.
Check for physical damage such as a broken mounting ear from dropping the head or a bent or broken stud and/or bolt. These defects should be repaired or the head should be replaced.
