1972 350 Chevrolet Pickup Engine - Tech - Build Your First Engine
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A close look at the piston, rings, and cylinder bore didn't reveal any failures, so we turned our attention to the valveguide clearance. Sure enough, the No. 8 exhaust valve rattled in its guide like a twig in a pipe, showing 0.010 inch of stem clearance. That's five times the proper 0.002-inch clearance we measured on the other 15 valves. Then we noted that the vintage cast-aluminum valve covers were nonvented and had no provision for the PCV (positive ventilation crankcase) valve. It looked like normal crankcase pressurization was forcing oil past the loose guide and making an oil-leak path into the No. 8 cylinder-oil fouled the spark plug every few months. Stop and explore any instance of isolated wear during initial teardown using the principles of root-cause analysis. You may discover the tip of an iceberg or a simple problem. And naturally, always use a PCV valve to vent the crankcase. View Related Article
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