The engine’s ignition system is often the culprit behind decreased performance and fuel mileage. If your engine is equipped with a points-style ignition system, breaker point gap, a faulty condenser, faulty spark plug wires, or a dirty or cracked rotor or distributor cap, symptoms would indicate a severe problem when one does not exist. An electronic- ignition-equipped engine can suffer similar maladies with the exception of problems with points or condenser.
A stretched timing chain and worn timing gears will cause a change in the valve timing of the engine and affect its performance even to the point that the engine will no longer run. Burned valves or a buildup of carbon deposits in the combustion chamber, weak valve springs, or excessive wear to camshaft lobes will also adversely affect engine performance. Engines equipped with solid valve lifters will react to changes of thousandths of an inch in adjustment by losing power and in extreme cases may suffer damage to related valve-train parts. A blown head gasket is a common engine problem that will manifest itself through an immediate loss of power. While this is a serious engine problem, when detected and repaired in a timely fashion it should not be a direct indication that the engine needs rebuilding.
Engine Noise
Your engine is full of moving parts and all of them have the potential to make noises that signal a problem, but due to the harmonics involved, engine noises can be very difficult to locate. Your first determination should be if the noise is at engine speed or half engine speed. As a general rule, noises that are at half engine speed usually emanate from the valve-train (with the exception of fuel pump noises or a condition called piston slap). Noises at engine speed normally indicate a problem in the bottom end or crankshaft area of the engine.
A timing light is an easy way to determine the speed of the noise. Hook up your timing light to a spark plug wire and start the engine. If you hear the noise once for each time the light flashes, the noise is at half engine speed, and if the noise occurs twice for each flash of the light, it indicates that the noise is at engine speed. Once the speed of the noise has been determined, you can get about locating its source.
The cylinder block can transmit internal noises harmonically, so it may be difficult to locate the source without a listening device. A mechanic’s stethoscope is often used to pinpoint engine noises, but if you do not have one at your disposal, a length of plastic tubing or a long screwdriver will get the job done quite well. I remember as a teenager learning how to use a screwdriver to locate the source of engine noises. A mechanic had diagnosed a noise in the engine of a friend’s car as emanating from a faulty wrist pin. Lucky for us, a local hot-rodder schooled me on the technique of placing the end of a long screwdriver against the engine while touching the handle end to my ear to pinpoint internal noises. In that instance, the fuel pump eccentric was the source of the noise and not a wrist pin as initially diagnosed. A length of plastic hose also transmits sound well. The technique here is to move your probe from place to place until the source of the sound is located.
If the noise is from a particular cylinder, it could be caused by the piston and rod assembly. You can tell by placing the tip of your probe next to a spark plug. If the noise is coming from the top of the engine, it is very likely valvetrain related and may be isolated and pinpointed by removing a valve cover and visually inspecting the valvetrain both with the engine running and shut off. With the engine off, check for signs of a bent pushrod or broken valve spring. With the engine running, ascertain that the pushrods are rotating and check for a rocker arm that may not be opening its valve as far as the others. Should either be the case, you may have a wiped (worn) camshaft lobe(s). In engines equipped with hydraulic valve lifters, a collapsed lifter(s) will result in a persistent tapping sound at half engine speed.
Piston Slap
Piston slap is caused by excessive piston-to-wall clearance and manifests itself as a hollow noise that is most prominent when the engine is cold and under a load. The causes of piston slap include wear due to poor lubrication or high mileage, or in extreme cases a collapsed or broken piston skirt. If the sound goes away soon after the engine warms up, the condition is not that severe. Note that engines equipped with forged-aluminum pistons, as opposed to the more common cast type, are more prone to slap until the engine has warmed up due to the increased piston-to-wall clearance required when using forged pistons. An easy method of determining if the noise you are hearing is piston slap is to retard the ignition timing a few degrees while the engine is running. Remember that Ford engines have a counterclockwise rotation, so to retard the timing, slowly turn the distributor in a counterclockwise direction. By retarding the timing, you are reducing the load on the pistons caused by combustion. If piston slap is the culprit, the noise should diminish.
Wrist pin noise will be most prominent at idle or low speed and will manifest itself with multiple knocking sounds that are quite distinct. If your engine has developed wrist pin noise, the bushing at the small end of the connecting rod may be failing or the pin may have come loose from the piston.
Bearing Noise
Engine bearings with excess clearance will cause a knocking sound that will be most pronounced when the engine is first started, either hot or cold, before a sufficient level of oil pressure has been reached. Bearing noises will also often manifest themselves under hard acceleration, but should not be confused with detonation, a condition that produces more of a rattling sound. Main bearings will knock at half engine speed with the somewhat muffled noise coming from deep within the block.
Connecting rod bearings will also knock when clearances are excessive or if there is insufficient oil pressure. A rod-bearing knock is most prominent upon deceleration after the engine has been run at a constant speed for a period of time. Piston rings that are broken, or have lost the tension required to hold them against the cylinder wall, will create a chattering sound that is most noticeable under acceleration. The easiest way to diagnose a piston ring problem is to conduct a compression check on the engine.
Diagnostic Tools and Steps
Now that I have covered some of the problems that your engine may be experiencing, it’s time to discuss how to diagnose the overall condition of the engine and the tools used to pinpoint potential problems. Using this information, you should be able to confidently assess the need for a rebuild.
Here is a good tip: start simple and do not overlook the obvious. There is no need to go high-tech immediately, as some of your engine’s simplest parts will reveal information that will speak volumes about what has been taking place under the hood.
Spark plugs are a window to what is occurring in each of the engine’s cylinders, so it’s smart to keep them in order as removed to assist in pinpointing potential problem areas. First check that the proper heat range spark plugs for your application are in the engine. Something as simple as incorrect spark plugs can adversely affect performance and fuel economy. Once you have verified that your engine is fitted with the correct spark plugs, conduct a visual inspection of each spark plug. There are several things to look for:
• A wet, black insulator indicates excessive amounts of oil in the combustion chamber or a plug that is not firing and has been fouled by fuel. You can ascertain the latter by holding the plug to your nose and conducting a sniff test to determine the presence of raw gasoline.
• Bubbling or blistering of the insulator is an indication of excessive heat in the combustion chamber and is usually attributed to an overly lean fuel mixture.
• If the plugs show a dry black or dark gray coating, the fuel mixture may be too rich or there could be a problem with the ignition.
• A serious problem, such as a blown head gasket, may also exist if two spark plugs from adjacent cylinders show a white foamy deposit while the other plugs are clean.
Check Ignition Timing
You will notice references to “ignition timing,” “setting your engine