Seriously burned valves will make the engine sound like an air compressor. Minor leakage can be detected with a cylinder leakage tester. It puts pressurized air into a spark plug hole, then you read the percent leakage on the gauge, and you can listen where the leakage is taking place.
Carburetor = intake valve
Tail pipe = exhaust valve
Oil cap = piston rings
Bubbles in radiator = head gasket
The service manual describes how to adjust the valves. You must turn the engine until a specific piston is at top dead center on the compression stroke, then use the chart to adjust certain valves on various cylinders.
Another method I've seen is to insert the proper size feeler gauge and adjust the valves while the engine is running. Tighten the valve until it develops a misfire, then back it off just until the misfire clears up, then remove the feeler gauge. I don't care for that method if you're being picky because the setting might change a little when you tighten the lock nut.
If your engine doesn't sound like a typewriter, the valves are probably fine. If there is a little wear in the valve train, it will affect valve timing. As the cam turns, it has to turn further than normal to take up the slack before the valve starts to open. I use the big "T" and "L" to remember the following:
"L" is for Loose valves, Late valve timing, and increased Low end torque.
"T" is for Tight valves, and increased Top end torque.
People who build high performance engines often use offset keys to turn the camshaft on the sprocket 2, 4, or 6 degrees. This changes the "personality" of the engine according to its intended use. My 440 police engine acts like any 318 up to around 50 mph, but after that it just about tears the seats off their hinges! That's what was needed in a high speed pursuit. I also have a 318 in a 4600 pound station wagon with a "gas mileage" cam. It is the same as a motor home camshaft and is designed for low end torque to get the thing rolling. I can squeal the tires all over the place when starting out, but you can tell there isn't much chance you'll be passing many people going up a steep hill.
Wednesday, January 6th, 2010 AT 3:03 AM