Now that all of the cylinder head components are clean, it’s time to inspect them for wear and/or damage. To accurately inspect them, you will need some specialized tools:
If you do not have access to the proper tools, you may want to bring the components to a shop that does.
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 you had to file them 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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Check for visible issues first; broken springs. Next 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.
Spring retainers rarely need replacing. They should still be checked as a precaution. Inspect the spring mating surface and the valve lock retention area for any signs of excessive wear. Also 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 and its respective valve should be replaced.
| Use a caliper to check the valve spring free-length
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| Check the valve spring for squareness on a flat surface; a carpenter’s square can be used
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Now that you know the valves are good, you can use them to check the guides, although a new valve, if available, is preferred. Before you measure anything, look at 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.
| A dial gauge may be used to check valve stem-to-guide clearance; read the gauge while moving the valve stem
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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. Also, 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. A seat concentricity gauge, if available, should be used to check the seat run-out. If run-out exceeds specifications the seat must be machined. When no specification is provided, use 0.002 in. (0.051mm) as a general rule of thumb for concentricity.
After you clean the gasket surface of the cylinder head of any old gasket material, check the head for flatness.
| Check the head for flatness across the center of the head surface using a machinist’s straight edge and feeler gauge
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| Checks should also be made along the head surface, diagonally
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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. A qualified machine shop will have all of the milling specifications for your vehicle's engine.
Generally, cracks are limited to the combustion chamber, however, it is not uncommon for the head to crack in a spark plug hole, port, on the exterior surface, or in the valve spring/rocker arm area. The first area to inspect is the one that gets the hottest- the exhaust seat/port area.
A visual inspection should be performed. Just because you don’t see a crack does not mean it is not there. Some more reliable methods for inspecting for cracks include Magnaflux®, (a magnetic process) or Zyglo®, (a dye penetrant). Magnaflux is used only on ferrous metal (cast iron) cylinder heads. Zyglo uses a spray on fluorescent mixture along with a black light to reveal the cracks and is suitable for aluminum cylinder heads. It is strongly recommended to have your cylinder head checked professionally for cracks, especially if the engine was known to have overheated and/or leaked or consumed coolant. Contact a local shop for availability and pricing of these services.
Physical damage is usually very evident. For example, a broken mounting ear from dropping the head or a bent or broken stud and/or bolt. All of these defects should be repaired or the head should be replaced.
