A number of factors are involved in deciding if your stock engine needs to be rebuilt. In this chapter I list common symptoms associated with a worn-out engine and some simple diagnostic steps to make an informed decision. A thorough inspection (particularly leak-down and compression tests) of your engine will help you determine its state of health and whether or not you need to rebuild it.
This Tech Tip is From the Full Book, 4.6L & 5.4L FORD ENGINES: HOW TO REBUILD. For a comprehensive guide on this entire subject you can visit this link:
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Today, many newer engines have 100,000 or more miles but it is highly unlikely to find a Y-block Ford V-8 with 100,000 miles or more. This has less to do with the overall design and strength of the engine series than it does the maintenance practices, materials, and systems used in engines designed in the 1950s. Quite simply, the advances in design, materials, manufacturing techniques, fuel delivery, and ignition systems found in today’s engines far overshadow anything even dreamed of as little as two decades ago let alone the 1950s. These advances include digital ignition, electronic fuel injection, engine management computers, and a myriad of sensors to monitor every aspect of engine performance. Although Y-block-powered vehicles are collectible and desirable today, in the 1950s and 1960s, they were used primarily as daily transportation for families and not seen as treasures in need of long-term preservation.
Excessive Oil Consumption
A car with high-mileage and/ or a poorly maintained Y-block uses oil and requires a rebuild. As a general rule, if your engine uses a quart of oil for every 1,000 miles or less, it is consuming an excessive amount.
Take note that I’m referring to an engine that “uses” oil, as opposed to “burning” it. You need to determine the root cause of the problem, rather than assuming your engine is burning oil.
Carefully and methodically examine the block, heads, intake, and all parts of the engine for oil leaks. A leaking rear main seal, valley pan gasket, or valve cover gasket that leaves a few drops of oil on your driveway can contribute greatly to oil consumption because engine leaking is constant and often much greater when the engine is running
For example, I recently noticed drops of oil under the draft tube in my engine so I looked into it. With the engine running, it appeared that the oil was leaking directly from the road draft tube itself, which seemed highly unlikely because it was a recently rebuilt engine. Closer examination revealed two fasteners had not been correctly tightened. In fact, the two heavy-duty Phillips-head screws that secure the road draft tube to the side of the block had somehow worked loose. A little thread sealer and aggressive tightening resolved the problem and soon the underside of the engine was dry. The 312-ci engine uses the old-style rope rear main seal only; the engine has a greater chance of leaks with this type of seal.
Internal oil loss may be the result of worn or cracked valvestem seals or guides, problems that are correctable without having to completely rebuild the engine. All engines have lubrication issues because of the clearance between the stems of the valves and their guides. Over time the clearance increases and oil is allowed to pass down the valvestem and into the combustion chamber where it is burned off. Likewise, the rubber seals on the valvestems typically become brittle and crack over time so oil is allowed to flow past the valveguides. You don’t have to remove the heads to replace the valvestem seals, and this may greatly reduce internal oil consumption.
There are two ways to replace the valvestem seals without removing the heads. First, you can move the piston to top dead center (TDC) and stuff rope down the plug hole to keep the valve from dropping while you use a lever-type compressor to free the valvespring. Second, you can use compressed air applied through a fitting in the spark plug hole to pressurize the cylinder, and then use a lever-type compressor to free the valvespring.
A puff of blue smoke from the exhaust pipe immediately after engine start-up is a common indicator that an engine has worn valve seals. A cracked fuel pump diaphragm is another cause of internal oil loss. When this occurs, the fuel pump’s internal vacuum sucks oil from the crankcase into the fuel stream of the carburetor, and this produces continuous blue smoke from the exhaust. Some owners may be alarmed and think that the engine has suffered a catastrophic internal failure because of the blue smoke. That is not the case unless the smoke is accompanied by the ominous sounds related to internal parts failure.
Low Oil Pressure
A drop in engine oil pressure may be caused by wear to rod bearings, wear to main bearings, a bad oil pump, or any combination of these. Sadly, during the era of the Y-block Ford V-8, some great mind in the auto industry decided to unburden the motoring public from the responsibility of having to read a gauge that actually displays engine oil pressure. A warning light replaced the time-honored gauge, and this light was electromechanically activated when engine oil pressure dropped below a preset limit. This warning light quickly became known as an “idiot light,” and my firm belief is that the term was derived from someone possessing at least a modicum of knowledge on how to properly monitor and maintain the average internal combustion engine. You must wonder how many engines expired over the years as a result of uninformed motorists believing in the powers of that magic light.
The following is from the 1956 Ford car shop manual as it relates to the oil pressure indicator light: “As the engine comes up to speed, the oil pressure increases, and after the pressure has risen to a safe value, the oil pressure activated switch opens up, allowing the light to go out. As long as oil pressure is maintained, the indicator light remains out. If at any time the oil pressure in the system drops below about 7 pounds, the switch closes, and the light comes on.” I don’t know about you, but this does little to instill confidence that my engine is being properly monitored in this critical area.
Of course, if you come from a hot rod background, you installed an aftermarket oil pressure and water temperature gauge almost immediately after buying your car. On many occasions the first indication that a Ford V-8 engine was losing oil pressure was the clattering caused by the hydraulic valve lifters as they began to collapse. If you drove Fords powered by the Y-block V-8, which had no provisions for hydraulic valve lifters, the first indicative sounds of low oil pressure were often far more ominous because catastrophic damage to the engine had already occurred.
If you are restoring a car to exacting standards, I recommend installing a full-time dedicated electric or mechanical oil pressure gauge under the dash. I keep an inexpensive aftermarket version and an assortment of adapter fittings in my toolbox so I can diagnose oil pressure problems on vehicles with idiot lights.
All I need to do is remove the oil pressure sender, which is located on the driver’s side of the cylinder block just to the rear of the oil filter. I install the necessary adapter fittings in place of the oil pressure light switch and connect the mechanical gauge in order to take accurate oil pressure readings. Readings should be taken when the engine is cold, and then again, when it has reached normal operating temperature. With the engine at normal operating temperature, pressure readings of more than 20 psi at idle are adequate. You should see an immediate increase in pressure with no fluctuation as engine RPM increase.
If your engine has low oil-pressure readings, a number of things may be the cause, such as dirty oil with decreased viscosity or a clogged filter or passage in the engine’s lubrication system. This is common in Y-block engines. More critical indications include excessive main or connecting rod bearing clearance. Although it isn’t a common failure, the oil pump or the drive that runs off the distributor may also be at fault. I make it a practice to replace the oil pump driveshaft with a heavy-duty replacement and carefully check the oil pump’s internal rotors for indications of wear or excessive clearance whenever I rebuild an engine. The dollars spent in this area reap dividends in engine life for years to come.
Decrease in Performance
If your engine has experienced a decrease in fuel economy and engine performance, it does not necessarily mean it is worn out and is in need of a rebuild. Many factors can contribute to a loss of power and fuel economy, some of which do not relate directly to the condition of the engine. You need to thoroughly and methodically inspect, test, and evaluate each major system of the engine. Once you’ve inspected each of them, you should conduct a compression and leak-down test to verify the current state of your engine. A clogged or restricted exhaust system could be the cause. Ascertain whether the exhaust manifold heat riser is free and not stuck in the closed position. Visually examine the exhaust pipe, and verify that it is not kinked or collapsed. An old, dirty, and clogged fuel filter, air filter, carburetor, or automatic choke restricts air and fuel flow to the engine. This produces changes to the air/fuel mixture and causes a loss of power and fuel mileage.
If your Y-block Ford or Mercury is a 1954–1956 model, remember that the oil in your oil bath air cleaner needs to be changed at fairly frequent intervals. Ford recommended changing the air cleaner oil every 2,000 miles.
In addition, if your fuel tank and lines are original, your classic Ford or Mercury may be suffering from five decades of rust, dirt, and corrosion. If this is the case, these parts desperately need to be replaced. In addition, the ethanol-based fuels we are forced to use have proven to be corrosive and destructive to older automotive fuel systems. I have found rubber fuel lines deteriorated from the inside while still appearing outwardly fine. Modern fuels have also destroyed Viton-tipped carburetor needles.
A worn-out or incorrectly adjusted clutch or a malfunctioning automatic transmission can slip and be responsible for decreases in power and fuel mileage.
The ignition system can also cause decreased performance and fuel mileage. If your engine is still equipped with its original breaker points style of ignition system, breaker points gap, a bad condenser, faulty plug wires, or a dirty or cracked rotor or distributor cap can substantially degrade performance. These symptoms can also mimic other more serious problems. Something as simple as a disconnected or broken vacuum hose leading from the carburetor to the distributor’s advance unit can lead you to believe your engine is on its last legs.
Timing chain and gear damage or wear can also decrease performance. A stretched timing chain and worn timing gears cause a change in the valve timing. If the chain has been severely stretched the engine no longer runs.
Damaged or burned intake or exhaust valves, a buildup of carbon deposits in the combustion chamber, weak valvesprings, and excessive camshaft lobe wear adversely affect engine performance. Solid valve lifters are installed in all Y-block engines, and the valve system reacts to changes in adjustment, or lash, of thousandths of an inch. In extreme cases, incorrect valve lash adjustment causes damage to related valvetrain parts.
A blown or leaking head gasket is a common engine problem that manifests itself through an immediate loss of power. Although this is considered a serious engine problem when detected, the engine should not need a complete overhaul if repaired in a timely fashion. The factory equipped all Ford Y-block V-8 engines with steel-shim head gaskets. Corrosives in the cooling system can take their toll on them over the years. It is prudent to replace the original-style gaskets with modern composite gaskets when rebuilding your engine.
Your engine is full of moving parts, and all of them have the potential to make noises that signal a problem. Due to the harmonics involved, engine noises can be very difficult to pinpoint. You should first determine if the noise is at engine speed or at half engine speed. As a general rule, noises that are at lower engine speeds usually emanate from the valvetrain with the exception of fuel pump noises and a condition called piston slap. Noises at higher engine speeds normally indicate a problem in the bottom end, or crankshaft area, of the engine.
Using an ignition timing light is an easy way to determine the engine speed when the noise occurs. Connect the 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 throttle. If the noise occurs twice for each flash of the light, it indicates that the noise is at full throttle. Once the engine speed has been determined, you can set about locating the noise. The cylinder block can harmonically transmit internal noises, so it may be difficult to locate the source without some type of listening device. A mechanic’s stethoscope is often used to pinpoint engine noises, but if you don’t have one, a length of plastic tubing or a long screwdriver can get the job done quite well.
As a teenager I learned the value of using a screwdriver to locate the source of engine noises. A mechanic had diagnosed a noise in the engine of a friend’s 1956 Ford as emanating from a faulty piston wrist pin. Luckily for us, a local hot rodder had schooled me in the technique. He placed the end of a long screwdriver against the engine while touching the handle end to his ear in order to pinpoint internal noises. He recommended using a screwdriver with a wooden handle, and I keep one in my toolbox to this day.
In that particular case, the fuel pump eccentric was the source of the noise and not the more serious wrist pin as originally diagnosed. The technique is to move whatever you are using as your probe (screwdriver, length of plastic tube, or stethoscope) from place to place until the source of the sound is located. If the noise is coming from a particular cylinder, the piston and connecting rod assembly could be causing it. Place the tip of your probe next to each spark plug to locate and isolate it. If the noise is coming from the top of the engine, the valvetrain or related parts are most likely the cause. Remove the valve cover and visually inspect the valvetrain to pinpoint the problem. Do this while the engine is shut off and while it is operating. With the engine turned off check for signs of a bent pushrod or broken valvespring. With the engine running, ascertain that the pushrods are all spinning 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 an excessively worn camshaft lobe(s).
During the years they were in production, the Y-block Ford engines suffered from an oiling problem. Copious amounts of sludge are often discovered under the valve covers. When this condition exists, chances are the lack of proper lubrication has caused damage, scoring rocker arm shafts and rockers.
I recall hearing rocker arms on a Y-block making a sound when running that was akin to a rusty gate hinge. It was times like this that “old school” mechanics installed a top oiler, also referred to as a Tennessee Oiler kit. Mechanics tapped into the side of the blocks to install them. These commercially produced Rube Goldberg–type contraptions diverted oil around the clogged internal passages and remedied the problem. A copper tube was plumbed into the valve cover where it routed the oil. If you come across a Y-block with one of these devices, chances are it is in serious need of a rebuild.
Excessive clearance from the piston to the cylinder wall causes piston slap, which manifests itself as a hollow noise that’s most prominent when the engine is cold and under a load. Piston slap causes 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, it is an indication that the condition is not severe. The Y-block came equipped with cast-aluminum pistons, but if forged-aluminum pistons have been installed, they are more prone to slap until the engine has warmed up. This is due to the increased piston-to-wall clearance required when using forged pistons because of their rate of expansion. An easy method of determining if the noise is piston slap is to retard the ignition timing a few degrees while the engine is running.
Remember that Ford distributors have a counterclockwise rotation so slowly turning the distributor in a counterclockwise direction retards the timing. 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
Wrist pin noise is most prominent at idle or low speed and manifests 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, which is retained by lock rings, may have come loose from the piston.
Engine bearings with excessive clearance or wear cause a knocking sound, and it is most pronounced when the engine is first started, either hot or cold, before a sufficient level of oil pressure has been reached. Bearing noises also manifest themselves under hard acceleration, but should not be confused with detonation, a condition that produces more of a rattling sound. Main bearings knock at half engine speed with the some what muffled sound coming from deep within the cylinder block.
Connecting rod bearings also knock when clearances are excessive or if there is insufficient oil pressure. A connecting rod bearing knock is most prominent upon deceleration after the engine has been run at a constant speed for a while.
Piston rings that are broken, or have lost the tension required to hold them tight against the cylinder wall, 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 Techniques
Now that I have covered some of the problems that your engine may be experiencing, it’s time to diagnose the overall condition of the engine and describe 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 perform a comprehensive visual examination of the engine. Don’t overlook the obvious. Some of your engine’s simplest parts reveal information that speaks volumes about what has been taking place under the hood.
Spark Plug Inspection
Spark plugs are the 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 isolating 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 verify that your engine is fitted with the correct spark plugs, i.e., the proper heat range for your application, 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 is not firing and has been fouled by fuel. You can ascertain the latter by 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 in the engine are burning clean. A properly burning spark plug shows a uniform, light brown color across the ceramic insulator.
Ignition Timing Check
I have made many references to ignition timing, such as setting your engine to TDC and rotating 90 degrees in a clockwise direction. Here’s how to take these readings on an engine. The Y-block Ford V-8 engine series timing increments are machined into the face of the vibration dampener. You read them from the passenger’s side of the engine when they align with a pointer affixed to the timing cover.
Clean the Dampener
Use a good cleaning solvent to clean the dampener so the marked increments are easier to read. You need to remove years of dirt and grime from the outside circumference of the dampener. You may find that it is easier to access the dampener from under the car (on the Y-block series engines you still have to deal with the front motor mount bracket, so it can be a little challenging) and necessary to turn the engine over in order to clean the entire surface of the dampener.
You can disable the ignition and use a remote switch to activate the starter and turn over the engine. However, I often attach a socket and breaker bar to the crankshaft bolt and turn over the engine manually so I have more control of where the dampener stops in its rotation. If you choose to turn the engine manually, remove the spark plugs so you are not fighting compression.
After you clean the dampener, the timing marks should be clearly visible. (You can use two different colors so they are easier to distinguish later.) TDC is marked on the dampener as TDC or the numeral zero. Refer to the TDC chart (and the timing increments marked as 2-4-6- 8-10) on page 135.
You can highlight the TDC line using a colored chalk marker. Automotive touch-up paint also shows up well and does not wear off easily.
Next, use a straightedge to divide the dampener into sections 90 degrees apart and place a short paint mark at each point. This makes it easy to move the engine through its rotation 90 degrees at a time.
The final step is to mark the timing increment that corresponds with the manufacturer’s specifications for your particular year, model, and engine. For this step you may want to use a white marker or paint so that it contrasts with the TDC and 90-degree markings and causes no confusion.
With the vibration dampener clearly marked, you are now ready to check ignition timing, verify TDC, and make accurate 90-degree rotations of the crankshaft.
Check the Breaker Points
The stock ignition system on your Y-block and other V-8s of the era is a breaker-points system. You must first check breaker point gap/dwell angle before checking the timing. Often the gap on the points is too small, or close. This is often caused by normal wear on the rubbing block, which contacts the distributor cam, retarding ignition timing.
Use a dwell angle meter or simple feeler gauge to set the gap/ dwell angle. If your engine has been upgraded to an electronic system (such as PerTronix Igniter or MSD), disregard the previous step.
With the points set, you are ready to check timing.
Use a Timing Light
Attach the timing light to the number-1 spark plug lead. In a Ford engine, the number-1 cylinder is located closest to the grille and farthest from the firewall on the passenger’s side of the engine.
Disconnect and plug the vacuum advance hose from the distributor. Loosen the hold-down clamp at the base of the distributor, and then make a thorough check to ensure that nothing is too near any moving parts before starting the engine. With the engine running at normal idle speed, trigger the timing light to initiate the flash and aim it at the timing pointer.
The strobe effect of the light causes a stop-action view of the vibration dampener as it rotates, allowing you to see the relationship between the timing increments on the dampener and the pointer. Rotate the distributor slightly until they are aligned.
Carefully tighten the distributor hold-down clamp, and recheck the timing to make sure it has not moved. Now reattach the vacuum advance hose to the distributor, and activate the timing light again.
You should see the timing advance slightly on the dampener. If there is no advance, there may be a problem with the distributor’s vacuum advance or low engine vacuum, which results in a loss of power and fuel economy.
A simple vacuum gauge is a valuable diagnostic tool and can reveal a number of mechanical problems from minor to major. When an engine is running it creates vacuum in the intake manifold. A vacuum test reveals any time one or more cylinders are not operating at peak power.
To check engine vacuum, connect the gauge to a port on the intake manifold, or carburetor, and start the engine. The vacuum reading should be 16 to 18 degrees of mercury at idle. Keep in mind that vacuum readings are lower at higher altitudes; they are also lower if a camshaft with a more radical profile (more overlap) than stock is installed.
A low initial vacuum reading may be indicative of nothing more serious than incorrect ignition timing, so get out that timing light and check, and/or adjust timing as needed. If you are getting slow fluctuations on the vacuum gauge, it may indicate a fuel mixture that is too rich. Try increasing the idle speed or turning the idle mixture screws on the carburetor in to correct the problem. If the gauge shows a consistently low vacuum reading, the engine could have a blown intake or cylinder head gasket that requires further diagnostic work.
With a vacuum gauge hooked up, revving the engine should produce a drop in vacuum with a steady reading on the gauge. If the needle shows a fluctuation, it could indicate that valvesprings are weak.
Cranking Vacuum Test
With the engine at normal operating temperature, you can perform cranking vacuum tests. First disable the ignition so that the engine doesn’t start, and then crank the engine with the assistance of a helper or remote starter. The reading on your vacuum gauge should remain steady. A fluctuation of the needle indicates a problem in one or more of the cylinders. In this case, the problem could be as simple as valve adjustment in an engine with mechanical valve lifters or a collapsed lifter in those equipped with hydraulic lifters.
Note: All Y-block V-8 engines use mechanical valve lifters. It could also indicate a wiped camshaft lobe, leaking valves, worn piston rings, a damaged piston, or blown head gasket. A damaged camshaft lobe(s) sends a hollow popping sound through the carburetor under load.
Power Balance Test
You can pinpoint a problem cylinder(s) by checking the power balance between them. Most engine analyzers have the capability of conducting a power balance test, but few of us own such expensive pieces of equipment. Fortunately, there is an alternative means for analyzing power balance. A pad, pencil or pen, and tachometer (a dwell tachometer suffices) are the only tools needed for this test on a breaker-points ignition system.
Start the engine and increase throttle until 1,000 rpm is reached. Use a pair of insulated-handle pliers to remove the spark plug caps one at a time and disable the cylinders. Be careful not to contact the live ends of the plug wires as they continue to carry current even when disconnected. Note the RPM drop, and then reconnect the plug wire. Repeat this process until you have disabled each cylinder and noted the RPM on each.
A healthy or properly operating cylinder creates a greater RPM drop when the spark plug wire is removed. When a cylinder is down on power, it contributes less to engine power. Thus, any cylinder that is down on power reveals itself by a smaller decrease in RPM.
This method should only be used to disable cylinders on engines that have conventional points-type ignition systems. Disconnecting a plug wire in a vehicle equipped with electronic ignition may cause a power surge that can damage the ignition. There are commercially available test kits that allow you to disable those cylinders by shorting out the plug wire without risking a power surge.
A compression test is the simplest and least expensive means of determining how well a cylinder is sealing. Be certain that the engine has reached its normal operating temperature before checking compression. For this test you need paper, pen or pencil, and a compression gauge. Be aware that when you are conducting a compression check, a combustible mixture of air and fuel is blowing out of the cylinders under pressure, and any spark or flame can result in an explosion. Make sure your work area is well ventilated and free of any ignition sources.
Disable the ignition, remove the spark plugs, and block the throttle in the open position, then install the compression gauge in the cylinder to be tested. Using a remote starter, or an assistant, crank the engine a minimum of three complete revolutions and note the highest reading on the gauge. Repeat this process until all the cylinders have been checked and the readings recorded.
The maximum reading for this test is not as important as the percentage of difference between the readings for each cylinder. All cylinders should read above 100 psi, with 160 to 165 psi being the norm for the Y-block V-8 engine series. Each reading should be within 75 percent of the highest, while 90 percent or better is optimum. If you find two adjacent cylinders that read considerably lower than the rest, chances are a head gasket has blown between the two cylinders.
If you experience a single cylinder with a low compression reading, an easy way to determine if the cause is related to the piston ring or valve is to squirt approximately a teaspoon of oil into the cylinder via the spark plug hole and repeat the test.
If the pressure reading increases, the piston rings are not seating to the cylinder wall. If there is no change, it is likely that a valve is not seating properly, or you have a blown head gasket.
A leak-down test is a more sophisticated means of checking how a cylinder is sealing than a compression test. It uses an external pressure source to test the rate at which a cylinder loses pressure. Because a leak-down leak tester is a more sophisticated tool, there aren’t many in home shops, but you can perform this test at home by using an air tank and spark plug hole adapter (with the exception of reading the actual percentage of leak down).
To perform a leak-down test the piston of the tested cylinder must be at TDC on its compression stroke, so that both valves in the cylinder are closed. This test is easiest to perform by following the engine’s firing order, so start by bringing the number-1 cylinder up to TDC on the compression stroke.
Next, disable the ignition by removing the coil wire, remove the spark plugs, and install a compression gauge in the spark plug hole.
Next, take off the radiator cap and engine breather/oil filler cap and block the throttle in the open position to assist in identifying what is leaking. If a leak is present remove the compression gauge. Fill the cylinder with compressed air using an adaptor between the hose and the spark plug hole. Caution: Keep hands away from the fan, belts, and pulleys during a leak down test, because if the piston is not at TDC, introducing air pressure into the cylinder may cause the engine to turn over. The cylinder should hold pressure and not leak down at a rate of more than 5 to 10 percent. More leak down than that indicates a problem in that cylinder.
With this method, you do not have a gauge to determine percentage of leak down. You can still make a fairly accurate assessment of any leakage by performing a few simple checks.
Listen for air escaping through the breather, carburetor, oil filler, dipstick tube, exhaust pipe, or radiator. Note that a small amount of air escaping through the breather is common in worn engines.
If you hear air escaping through the carburetor, an intake valve is leaking. Air coming from the exhaust indicates an exhaust valve is at fault. To be doubly certain that neither of the valves are leaking be sure that the cylinder being checked is still at TDC on the compression stoke.
If a blown or leaking head gasket is the problem, air leaks into a cylinder adjacent to the one being tested or through the cooling system via the radiator filler neck.
Air leaks at the dipstick tube or breather are indications that the piston rings are not sealing properly against the cylinder walls.
Once you have completed the test on the number-1 cylinder and noted the results, you can proceed through the fring order: 1-5-4-8-6-3-7-2, testing each cylinder as you go by rotating the engine clockwise to the next 90-degree mark on the dampener. Verify the cylinder by removing the distributor cap, and confirm that the rotor is facing toward the position on the cap that holds the plug wire for that cylinder.
Cooling System Pressure Test
Blown or leaking head gaskets that have adjacent cooling passages in the cylinder block also show up during a cooling system pressure test. A head gasket problem reveals itself as air and/or coolant escaping into the affected cylinder. This simple diagnostic test also identifies other leaks in the cooling system.
A pressure tester is designed to perform this test. Simply install the tester in place of your radiator cap, pump up the pressure, and check for leaks.
Written by Charles Morris and Posted with Permission of CarTechBooks