Originally published Jan/Feb 1999
Valve Train Disassembly
After valve subassemblies are removed, the lifters usually come out quite easily. If you hope to use the same lifters and cam, maintain ID on the lifters so that they can be reinstalled on the cam lobe that they
are mated to. After the lifters are out, the cam will slide forward and out. If you intend to you reuse the cam bearings, avoid striking them with cam lobes -- the lobe edges are sharp, and can ruin cam bearings.
Next you need to clean all of the valve train parts that you hope to reuse. Alkaline cleaners take off the oily grime, and carbon can be removed mechanically or with carburetor cleaner.
Checks should include: condition of the gear
teeth that drive the oil pump idler gear and, for 49-53, the distributor drive gear. Some visible wear is permitted; if pitting or severe wear is noted, the gear should be replaced. These gears can also be damaged by careless handling. Mechanical damage in the center 2/3 of a tooth is cause for replacement.
The straightness should be checked with the end journals on vee blocks using an indicator on the center journal. We allow not more than .001" TIR (total indicator reading). If
it is less straight than this and otherwise good, a cam or crank grinder can straighten it for you. The fuel pump eccentric between the halves of the rear cam journal should be reasonably smooth and TIR should be .200"; we use a wear limit of .180".
The journals should be smooth and 1.796 to 1.797", wear limit is 1.795". If under that, the journals may be ground to an undersize, then polished. Cam bearings are available .010, .020, and .030" undersize ID.
The lobes should not be pitted, nor worn excessively at the nose. You may compare the more worn lobes with less worn lobes, on the same cam, to get an idea of wear.
If present, check the cam gear mounting bolt holes for good threads and no cracks to the O.D. These are not strong enough to turn a tight camshaft, using two bolts and a bar, but that may have been tried.
Lifters should be checked for a convex bottom surface with no pits or grooves. The bottom
edge should not be chipped. The convex radius on the bottom is important to ensure that the lifter doesn't contact the edge of the cam lobe. If you are reusing the lifters on the same cam, then that radius can be flattened somewhat but should not be flat. If you are using the lifters on a fresh cam, do the cam and yourself a favor and buy new lifters or have the old ones resurfaced to the proper convex radius. The top of the lifter can be ground with the same radius at this time. If your
lifters are adjustable, check that there is at least 5 ft-lb of torque required to move the adjusting screw before you spend the money to resurface.
You usually can not change adjusting screws from one lifter to another. When in doubt, replace.
Measure the stems for wear. If worn more than .001", discard. If there are galled, or rough, areas on the stem, don't use them either. After face grinding, check the margin. The margin is the surface between the face
and the top of the valve head, the OD of the valve head. It should be at least 70% as thick as new. Different years had different materials and designs of valves, so it is difficult to give a dimension is correct for all.
If you have a 48 and earlier engine and most of your valves are bad, consider using a 49-53 upper valve train.
Springs should be checked for force at the specified height and "cock" or out of square between ground end and the
longitudinal centerline of the spring. The specifications we use are 37 @ 2-1/8" for 33-48, 40 @ 2-1/8" for 49-51 with one piece retainers and 39 @ 1-7/8" for 52-53 with two piece retainers. Rusty springs should be discarded, rust pits tend to cause fatique failures.