ENGINE BLOCK
- Given specific engine block malfunctions, identify the cause of the malfunction.
- Given a variety of engine malfunctions, identify the remedy for each malfunction.
Probably the most important thing for a mechanic to know is how to diagnose troubles in a motor
vehicle. This diagnosis consists merely of performing checks and tests in a logical, systematic
sequence. Let's begin discussing one of the most probable causes for engine malfunctions--the
cylinders.
1. Cylinder Malfunctions
Although the cylinder block is not actually a functioning part of the engine, the functioning components rely on it heavily. Therefore, the block can be the source of some engine malfunctions. For example, take the cylinder walls. The piston rings rely on the smooth surface to enable them to move up and down with the piston and yet maintain a pressure-tight seal. If this pressure-tight seal is lost, there will be a loss of compression and power. There will also be a loss
of engine lubricating oil. If a cylinder wall becomes scored (deeply scratched), what would be a good indication of this condition? If you said excessive consumption of oil through burning, you are off to a good start. Scores in the cylinder wall allow oil to bypass the rings and enter the combustion chamber where it is burned with the fuel-air mixture. This will eventually cause the cylinder to misfire. There will be evidence of misfiring due to loss of compression during the compression stroke and pressure during the power stroke. However, in the early stages this will only show up on test equipment during engine analysis.
2. Cylinder Troubleshooting and Remedies
If you suspect oil burning, take a look at the inside of the tailpipe. It will be covered with a coating of black soot. To further confirm your suspicions, have the motor vehicle operator "rev" or "gun" the engine. A light blue smoke will come from the tailpipe. Once your suspicions are confirmed, you must be certain the oil burning is not caused by some other defect. Perform a compression test on the engine. This will also help you to locate the defective cylinder. Now, break out the compression gage kit and check the parts of the kit, making sure the gage reads zero and the adapters are clean and free of cracks. Adapters vary in shape and size to allow
the compression gage to be used on various type engines.
Your next step before starting the engine is to check the vehicle batteries. They must be in good condition and the crankcase oil must be at the full mark on the dipstick. Start the engine and let it warm up to operating temperature. This allows normal expansion of the metals and will give you a true reading when you perform the test. After operating temperature has been reached, turn the ignition switch to the off position. Loosen all the spark plugs a turn or two, and, with a low pressure air hose, blow all dirt and other foreign matter from around the spark plugs. Remove all the spark plugs and clean any grease or oil from the spark plug hole with a clean rag. Now open the throttle and choke to set the throttle plate and choke in the wide open position. Switch the ignition off or remove the primary wire (cable coupling) from the distributor. This will prevent current from flowing across the points and a high tension spark will not be produced. You will perform a "dry" compression test first. Choose the proper size adapter of the compression gage. Insert the compression gage into the spark plug hole of the number one
cylinder and have a helper crank the engine over about ten times. During this process, if the operator carefully observes the gage hand, a sticking valve may easily be detected. The hand progressively rises with each revolution of the starting motor until no further movement of the gage hand is obtained.
Inserting compression gage into spark plug hole
The indicated pressure on the gage represents the maximum compression pressure under prevailing conditions. Should the gage hand remain fixed at any one of the "beats" or revolutions of the starting motor and then rise again, the point where it lagged would indicate a valve sticking in the open position. Compression pressures will vary and will be higher in newer engines compared to older ones. Write down the amount of pressure indicated by the gage. Repeat this procedure on each cylinder, counting the number of turns on each cylinder, until all cylinder compression readings have been recorded. If the readings do not vary in pressure more than 10 pounds per square inch (psi), your oil consumption is probably due to other causes. If the variation is more than 10 psi, a "wet" compression test should be performed. This test is performed in the same manner as the "dry" test except for one step. Before inserting the gage into the spark plug hole, squirt about four shots of oil from a trigger-type oil can into the hole and have the operator spin the engine with the starter switch. Now you are ready to insert the gage and proceed as if you were taking a "dry" test.
Preparation for a "wet" test
Perform the test on only those cylinders that had a low "dry" reading. The results of the test may show a rise in pressure or the readings may remain the same. If a rise in pressure is shown, there is a possibility of scored walls that allow pressure to bypass the piston. The cylinder head must be removed to make a visual inspection of the cylinders. If the pressure remains the same in the "wet" test as it was with the "dry" test, the source of the problem is defective valves or valve seats. However, low readings on adjacent cylinders usually indicate cylinder head gasket leakage between cylinders. If the walls are scored, the defective cylinder must be rebored. Let's stop for a second and see what you've learned so far. What would cause a loss of compression in a cylinder? Good! A scored or deeply scratched cylinder wall. How would you remedy this problem? Right again. You would rebore the defective cylinder.
3. Water Jacket Malfunctions
Water jackets, when properly maintained, will seldom be a source of malfunctions. Proper maintenance of the water jacket consists merely of keeping it filled and free of rust and corrosion. This is accomplished through a daily check of the coolant and the use of antirust chemicals. When chemicals are not available, periodic flushing of the cooling system is necessary. When a motor vehicle operator approaches you and complains that his engine is overheating, consider first whether it is an air-cooled or water-cooled engine. Let's say it is a water-cooled engine. You know that water or a commercial coolant is used in the system and it circulates through the engine block and cylinder head surrounding the cylinders and combustion chamber. A quick visual inspection will eliminate the fan, fan belt, and water pump. Apparently
then, if the engine is "running hot," this coolant is not circulating. There are two very good reasons for coolant not circulating. What do you think the reasons would be?
Engine water jacket
4. Water Jacket Troubleshooting and Remedies
If you decided that the thermostat is faulty or the water jackets are dry or clogged, you are right. First, start the engine and fill the radiator. Watch through the radiator opening to see if the water is circulating. If it isn't, you should troubleshoot the thermostat first. Do this by simply removing
the thermostat and checking the radiator again for circulation. If you still don't have circulation, the water jackets must be clogged and the entire cooling system must be flushed. Allow the engine to run for 10 to 15 minutes so that pressure will build up inside the water jackets. Now check the outside of the engine for leaks. Note: Leaks will usually occur in the core plugs. They cannot be repaired but must be replaced. If there are no visible leaks, the engine must have an internal leak.
Possible areas of coolant leakage
The walls of the jacket could be cracked into the cylinder wall. The way to check for a cracked water jacket is to remove the radiator cap with the engine running and look inside
Cutaway of radiator showing bubbling as opposed to normal swirling of coolant
If bubbles are present, they are most likely due to a blown head gasket but in some cases may be caused by pressure escaping through a crack in the cylinder wall and into the water jacket. This is the path of least resistance during the compression and power strokes. Of course, during the intake stroke, the water will be drawn into the cylinder.
Cracked water jacket
Let's confirm the defect now. Is steam being emitted from the tailpipe? Steam may look like burning oil, but it disappears soon after it leaves the tailpipe while smoke from burning oil lingers. What if you are losing coolant internally and there are no bubbles and no steam? Take another look at the water in the radiator while the engine is not operating. Perhaps you can detect an oily film on the water. It could be that the water from the water jacket is leaking into the oil passages, or that oil is leaking into the jacket. Pull the "dipstick" out of the engine and examine the oil on the end of it. If it appears milky or foamy, you can assume that a leak exists between the water jacket and oil passages. In rare cases, this may be the result of a cracked engine block, but it is usually due to a broken head gasket. In the cases of this type of crack, the block can probably be sealed. If it is the head gasket, both the cylinder head and the block must be checked for a smooth, flat surface and then ground (machined smooth) if necessary. What would cause bubbles to be in the radiator? If you said water jacket crack in the cylinder wall, you are absolutely right. What would be another way of confirming this? Very good! With the engine running, check the tailpipe to see if steam is being emitted. A cracked cylinder block may have to be replaced, but in some cases the defect may be remedied. How? You're good! By sealing the cylinder block.
5. Air Cooling System Malfunctions If an overheating problem exists in an air-cooled engine, and the fan and belt are serviceable, the cooling fins may have a build-up of dirt or other foreign matter between them. Air must be able to pass between the fins to carry the heat away from the engine.
Cooling fins
A shroud (a contoured sheet of metal which channels airflow) usually covers the entire engine, or at least the larger portion of it. This shroud directs the flow of air around the engine and through the cooling fins. Naturally, if the shroud is loose, it will not hold enough air inside to properly cool the engine. The part of the engine near the fan may be cool, but the remaining portion of the engine will likely overheat. Each fin cools a particular portion of the engine, and, if the fins become chipped, that portion of the engine will form a "hotspot." This is extremely critical in the cylinder head since a hotspot in the combustion chamber will cause the fuel to ignite prematurely, affecting engine performance. Oil is also a major factor in the cooling of an air-cooled engine. An oil cooler, which is very similar to a miniature radiator, is provided. Here again, a little preventive maintenance solves
problems before they begin. Prescribed periodic oil and oil filter changes will prevent oil from clogging and reducing oil circulation. Poor oil circulation will cause the engine to overheat by not lubricating high friction surfaces properly.
The condition of clogged oil passages may be detected by an abnormally high or low pressure reading on the instrument panel's oil pressure gage and verified by removing the rocker arm cover. Either some or all of the rocker arms may not be receiving oil if the pressurized passages are clogged. If the return passages are clogged, oil will be found "standing" on the top of the cylinder head where the rocker arms are located. To remedy this situation, you may have to remove the rocker arm shaft, soak it in a strong parts cleaner, and clear all oil passages with a soft wire. The oil should be changed immediately after this is done and as frequently as possible until the oil additives have had ample time to clean the system.
6. Air Cooling System Troubleshooting and Remedies
Conduct a visual inspection of the cooling fins for dirt and/or damage. Dirt clogging the fins is usually remedied by cleaning the fins with a high-pressure air gun. Inspect the shroud to ensure it is firmly in place. Check the oil cooler. It must be cleaned periodically with an air gun, or the engine will overheat. The oil passages must be kept extremely clean. This is accomplished by timely oil changes and oil filter changes. What would cause a "hotspot" to form in a certain area of the engine? Great! A chipped or broken cooling fin is correct. What causes clogged oil passages? That's correct, dirty oil.
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