DUDE! Click the yellow bar at the top, turn on Active X Control, and allow blocked content The Engine The Engine [Cylinder Heads] [Engine Blocks] [Ignition System] [Cooling System] [Fuel System] For Further Study: [4 Stroke] [Short Block] [Valvetrain] Click to Print QUESTION SHEET HISTORY Virtually every vehicle you have ever been in has been powered by an Internal Combustion Engine. This invention is one of the greatest advancements of the industrial world since, like, pants. Back when the Dead Sea was still sick, all our work was either done by our own hands or with the help of animals such as horses and oxen. By the early 1700's we were able to effectively harness the steam from boiling water to do work for us this was an External Combustion Engine, where the burning of the fuel was done outside the engine itself (it was the steam we used). The engine as we know it was patented in 1876 by Nikolaus Otto with a 4 stroke design, and in 1879 by Karl Benz with a 2 stroke design (Karl had a daughter named Mercedes...). By 1885 we were already trying to supercharge it for more power, thanks to a design by Gottlieb Daimler. Oh, hey: "Engine" (from Latin ingenium, meaning "ability") means any piece of machinery. "Motor" (Latin motor meaning "mover") is any machine that produces mechanical power. An "Electric Motor" is a correct term, while a "Combustion Engine" is not a correct term. It should really be
called a Combustion Motor. I will be using the terms Motor and Engine interchangeably. TERMINOLOGY I am going to use a variety of terms, and refer to engines in a number of different ways. Arrangement How multiple cylinders are arranged. They are commonly inline with each other (ie: "Straight 6", split into a "V" (ie: "V8"), or Horizontally Opposed (ie: "boxer" or "pancake") Displacement How large an engine is. Usually measured in Liters (L), or Cubic Centimeters (cc), or Cubic Inches ("ci" or "cid"). Traditionally, engines were refered to by their displacement in Inches, whereas today, most engines are measured in Liters. I usually refer to engines by how they were originally designated the engine in a '70 Mustang will be a 302ci, while the engine in a '90 Mustang will be a 5.0L even though they are the SAME engine. Cubic Inches. Bore The diameter of the cylinder. An engine that has been "bored out" has had the cylinder bore (diameter) machined larger and oversize pistons installed. This increases the displacement, and makes more power. Stroke Distance the piston travels on a stroke, or the distance from TDC to BDC. The stroke is twice the distance of the throw. An engine that has been "stroked" has had the crankshaft custom machined to move the piston a greater distance. This increases the displacement as well as the compression ratio which produces more power. Throw The distance from the center of the main journal of the crankshaft to its rod journal. The throw is one half the distance of the stroke Top Dead Center (TDC) Point of uppermost travel of the piston and crankshaft Bottom Dead Center (BDC) Point of lowermost travel of the piston and crankshaft The FOUR STROKE CYCLE While all Automobiles and Motorbikes complete the cycle of combustion, they will do it in one of two ways: 4 Stroke
Combustion occurs in four separate strokes: 1. Intake 2. Compression 3. Power 4. Exhaust This requires FOUR motions of the piston, which requires two full revolutions of the crankshaft just to ignite the air and fuel once. A Four Stroke engine 2 Stroke Combustion occurs in two separate strokes: Exhaust and Intake occur sort of together, and Compression and Power occur very close together. This requires only TWO motions of the piston, which requires only ONE full revolution of the crankshaft to ignite the air and fuel once. Two strokes are horribly inefficient at low speeds, which is why your two stroke dirt bike is a dog at low speeds outside of its "power band." Notice that the air and fuel and oil is drawn into the crankcase of the two stroke engine. The oil is there to lubricate everything. Some of the oil gets drawn into the cylinder and burned (making the exhaust blue). Notice the back wave from the exhaust going back to push the escaping air and fuel back into the cylinder. Without a proper exhaust system, a two stroke will not make any power at all, ever, since all the air and fuel will just float right on out the exhaust. INTAKE STROKE
The Intake valve is open The Piston is going down so the volume of the cylinder is getting large. A vacuum, or pressure of less than atmospheric, is created in the cylinder Atmospheric pressure forces air into the cylinder trying to fill the vacuum Fuel is mixed with the incoming air, and the cylinder is filled with the mixture of air and fuel The Intake Stroke is key to making power we want to fill the cylinder as full as possible. If we can make it easier for air and fuel to get into the cylinder (or physically pump more air in, such as supercharging or turbocharging), we will make more power. COMPRESSION STROKE Both valves are closed
Air/fuel mixture is trapped in the cylinder The Piston is going up so the volume of the cylinder is decreasing The air and fuel is compressed to about 1/8 its original volume About 150 psi is built up. As the mixture is compressed, it heats up The Compression Stroke is also key to making power the higher we can compress the air and fuel, the more power we get out of it. Until something breaks, of course. POWER STROKE Both valves are closed Spark plug fires, igniting the compressed air/fuel mixture
The Piston is forced down by combustion, pushing the connecting rod down to rotate the crankshaft This is not an explosion, but a smooth, controlled burn The Power Stroke is also key to making power If the air and fuel is ignited too soon (called "Advanced"), the pressure will happen before the piston is in an optimal place, costing us power. If it is ignited too late (called "Retarded"), the pressure chases the piston down the cylinder, costing us power. EXHAUST STROKE The exhaust valve is open The Piston is going up, so the volume of the cylinder is getting smaller
The Piston pushes the burned exhaust gasses out past the open exhaust valve, and out through the exhaust system and into the atmosphere The intake stroke of the next cycle follows this exhaust stroke The Exhaust Stroke is also key to making power Getting all the exhaust out of the engine quickly and easily allows us to fill the cylinder with fresh air and fuel as fully as possible. COMPRESSION RATIO You may hear people bragging about having a "high compression engine." This is, indeed, something to brag about. All things being equal, the more you compress the air and fuel, the more heat you put into the air and fuel, the bigger the combustion power will be. This is a very good thing for power. There are practical limits once the fuel starts exploding by itself (instead of burning in a controlled manner), damage occurs. The amount the mixture is squeezed on the compression stroke All other things being equal, the more the fuel/air mixture is compressed, the more power the engine produces As the mixture is compressed, it becomes hotter. If it becomes hotter than the flash
point of the fuel, it explodes prematurely, and engine damage results. This is called pre ignition, or detonation; or more commonly, knock, or ping. This is the limiting factor to how far you can go with increasing compression ratios. (Total Cyl. Vol. at BDC) Compression Ratio = (Total Cyl. Vol. at TDC) Compression Ratios of Different Engines: 4:1 Vintage cars because of poor quality of fuel, and hand crank starting system 8:1 10:1 Modern Production Cars higher compression ratios with computerized engine management to prevent knock and ping Up to 12.5:1 Muscle Cars from the late 1960's until low emissions became more important, compression ratios were reduced, to reduce NOx (Learn about Emission Controls) Up to 17:1 Race Cars because they use better quality high octane gasoline or alcohol Up to 25:1 Diesel Engines diesels take only air in on the intake stroke, and use the high temperature of the air on compression stroke to ignite fuel which is injected directly into the combustion chamber Video: Compression Ratio
ENGINE SIZE (Cubic Displacement) There is no replacement for displacement. Bigger is always better. Too much might be just about right. An over worked small engine will get poor fuel economy, and have no power to show for it. A loafing big motor will get good fuel economy, and have lots of power in reserve when you need it. What is engine displacment? The total amount of air/fuel mixture the engine is theoretically capable of taking in during one cycle The volume of all the cylinders, but not the combustion chambers, put together Measured in Cubic Inches (cu. in.) in imperial measurement, or in Cubic Centimeters (c.c.'s) or Liters (l) in metric measurement The amount of power an engine produces, is a direct function of how much fuel the engine burns, and the larger the cylinders are, the more fuel and air they can take in, and therefore burn. One engine that is twice as big as another, does not necessarily have twice as much power though, because it also has much more internal friction, or drag. It does, however use twice as much fuel. Jay Leno's Tank Car Displacement Formula (Volume of a cylinder, you did this in Math 9): V = (Volume of a cylinder) x (number of cylinders) V = (πr 2 h) x (n) Example V = (πr 2 h) x (n) V8 Engine V = (3.14 x (4.030 2) 2 x 3.75) x (8)
Bore: 4.030 inches V = (3.14 x (4.06) x 3.75) x (8) Stroke: 3.75 inches V = (47.81) x (8) V = 382.5 cubic inches ci x 16.39 = cc You can convert between different displacment measurements, too: Cubic Inches (ci's) x 16.39 = Cubic Centimeters (cc's) Cubic Centimeters (cc's) 1000 = Liters (L) A Ford 5.0L is also known as a 302cid (382.5)(16.39) = cc cc = 6269.2 cubic centimeters cc x 16.39 = L (6269.2)(16.39) = L L = 6.3 Liters ENGINE PARTS The basic engine has been pretty much standardized since the 1800's. There are some differences between manufacturers, but once you understand one automotive engine, you can understand all automotive engines the basic parts and principles are the same. This picture shows the basic parts common to most engines today. Cylinder Block: Strong and rigid, houses the crankshaft, connecting rods, pistons and cylinders. Usually made of Cast Iron or Aluminum. This bolts into the vehicle, and the transmission bolts to this. Cylinder Head: Houses the intake and exhaust valves and ports. Crankshaft: Receives the force from the piston and connecting rod and rotates. Additional weight is opposite the Throw (the piston end), to counter the weight of the piston and connecting rod, called "counterweight." A typical Over Head Cam (OHC) engine. Flywheel: A heavy mass that provides
enough momentum to keep the crankshaft turning during the non power strokes. The clutch is bolted to this to drive the transmission. The starter also engages teeth on the flywheel to start the engine. Connecting Rod: Changes the reciprocating motion of the piston to the rotating motion of the crankshaft. Piston: Draws air and fuel in, compresses it, receives the force of combustion, and pushes the exhaust out. Piston Rings: Seals the cylinder so nothing from the cylinder gets into the crankcase, and nothing from the crankcase gets into the cylinder. Intake and Exhaust Valves: Allow the air and fuel into and out of the cylinder. At least one of each valve, however, the more valves you can fit the more power you can make and the higher you can rev. Masarati experimented with 6 valve engines. Camshaft: Open the valves at the correct time. May be located in the Cylinder Block, or the Cylinder Head depending on the engine. Lifters: Are acted upon by the camshaft, and push on the valves. These are sometimes adjustable for clearance. Rocker Arms: Used when the valve is not directly in line with the camshaft it acts like a lever to get the camshaft motion to where the valve is. Valve Springs: Close the valves CYLINDER ARRANGEMENT The throws on the crankshaft are arranged so that the pistons do not all move up and down at the same time (this would make the engine horribly unbalanced, and shake itself to bits). Arranging the throws allows the proper strokes of each piston to occur at even intervals in most engines, which tends to minimize vibration.
In a 4 cylinder engine, The cylinders are numbered from front (pulley end) to back (flywheel end). If the spark plugs fired in numerical order (1, 2, 3, 4), the engine would be out of balance and vibrate excessively. Vibration is reduced by firing the spark plugs in an order of 1, 3, 4, 2 (shown in the illustration). Almost all inline 6 cylinder engines have a firing order of 1, 5, 3, 6, 2, 4 balancing outer cylinders and inner cylinders, on opposite ends of the engine. Of all the different cylinder arrangements, the least efficient has to be the inline arrangement. They are relatively long and large. Heavy counterweights must be used on the crankshaft to offset the weight of the pistons to keep the engine from vibrating. Many of the larger cars from the 50's and earlier had Straight 8 engines an inline 8 cylinder! That is why the cars of the day had a long, high engine hood to clear that monster of an engine.
V type cylinder arrangements make for a much shorter engine and therefore, a shorter, stiffer crankshaft. They don't need as heavy a counterweights on the crankshaft because the weight of one bank of pistons partially offsets the weight of the other bank. The "Horizontally Opposed," "Flat," "Boxer" or "Pancake" arrangement is the most efficient of all. It has a short stiff crankshaft, and the weight of one bank of pistons totally offsets the weight of the other bank. This engine is said to be inherently well balanced. Because of its efficiency and light weight, the horizontally opposed engine is used almost exclusively in light aircraft. While light weight is important in cars, it is even more important in aircraft. Lighter weight means more payload, longer range, and more performance. Larger aircraft in the bad old days used radial engines with up to three banks of nine cylinders (twenty seven cylinders), with up to 3500 cu.in. and 3000 horsepower.
Video: Engine Configurations OTHER ENGINE DESIGNS Four Stroke Engine:
Two Stroke Engine:
Wankel Rotary Engine:
Gnome Radial Engine:
ENGINE TESTING When an engine is brand new, all the parts have been machined to the exact size they need to be, with the exact clearances they need between each other. Out with the bad... As an engine is used, these parts will start to wear. We can make the engine last longer by
using high quality engine oil to lubricate the engine well, change the oil frequently so that the oil and oil additives are fresh. We can also treat the engine nicer by letting it warm up before we abuse it, and try to get it to heat up quickly (the most wear occurs when the engine is cold). Low but steady: the spark plugs are firing too late, or the valves are opening too late, or vacuum leaks Eventually, the wear in the engine will become so great that performace and economy will begin to suffer. Lucky for us, it is really easy to test an engine and see what kind of shape it is in before we even get dirty trying to fix it. There are three tests we commonly do:...in with the good VACUUM TEST A Vacuum test tells how badly an engine sucks. Hahahahahaha. No, seriously. We use a simple vacuum gauge, connect it to the intake manifold and measure how much, and how consistantly the engine draws vacuum. Observe the results: ENGINE CRANKING (but not running) If the cranking speed is normal, the engine vacuum should be about 5in Hg (inches of Murcury) and even. Uneven = a problem in one cylinder, low = mechanical problems. ENGINE IDLING Normal: steady 16 to 22 in. Hg (inches of Mercury the unit of measurement for vacuum).
Normal but Fluctuating: A problem in one or two cylinders. Broken ring, leaking valve or faulty fuel injector ENGINE CRUISE Rev to 2500rpm for 15 seconds Vacuum Steady: This is good Vacuum Drops: Plugged exhaust Now release the throttle and let the engine fall back to idle Vacuum Jumps, Then Normal: this is good Vacuum Does Not Jump: Worn rings, cylinders or valves Video: Vacuum Testing (user: Rondisco98 YouTube) COMPRESSION TESTING While a Vacuum Test can give you a pretty good idea about the condition of the engine, a Compression Test can give you a very good idea about the condition of a cylinder. A Compression Test involves measuring how much the cylinder actually compresses the air inside the cylinder. This pressure is measured in Pounds per Square inch (PSI). Most engines are around 150psi, but engine specifications (specs) can range between 100psi and 220psi depending on the engine. When I buy used cars, I bring along a Compression Tester and tools so I can test the engine right there. Finding problems can help work the seller down in price. On my own engines I do a compression test every year just to keep tabs on the condition of the engine I write the results on the underside of the hood as a reference. A Compression Tester 1. Disable fuel and ignition system we don't want any KA BOOM! 2. Remove ALL spark plugs we don't want the engine to have to work against anything
3. Open the throttle fully we want to make it easy for air to get in 4. Crank the engine and listen for 4 strokes as it cranks 5. Record the results WITHIN SPEC This is good LOW READING Compression is leaking out somewhere (either rings or valves). This is costing you power. Squirt about a tablespoon of oil into the cylinder and re test. If the new reading goes up significantly, this means the piston rings are leaking (the oil sealed them). Video: Compression Testing (user: blue280z YouTube) If the reading does not go up significantly, the valves are leaking (the oil cannot seal the valves). Try adjusting the valve clearance (also called lash) perhaps the cam is not allowing the valves to close all the way. If this does not fix it, the valve is probably screwed and needs to be fixed. HIGH READING This is not common. If the engine is an oil burner, it could be that there is carbon built up inside the combustion chamber and providing less space to compress the air and fuel into (it's compressing it higher). LEAK DOWN TESTING This is the ultimate test. A Leak Down Tester pumps compressed air into
the cylinder of a non running engine, and measures how much of that air is leaking out. It can tell you a LOT about an engine, including specifically WHERE the air is leaking. 1. Set the engine so the piston you are testing is at the top of its compression stroke (Top, Dead Center of it's rotation (TDC)). 2. Remove the spark plug 3. Connect the tester to the engine 4. Connect the machine to compressed air 5. Record the results 5 20% This is good. Anything below 10% is quite good. I've NEVER seen 0%. >20% LEAKAGE Look and Listen to see where the air is going Crankcase Air: leakage past the rings listen at the oil cap Radiator Bubbles: leakage past the headgasket or through cracks into the cooling system watch at radiator cap Intake Air: leakage past the intake valve listen at throttle plate Exhaust Air: leakage past exhaust valve listen at tailpipe Try testing a cylinder with the piston at the top of the cylinder, and again with the piston at the bottom of the cylinder. If there is more leakage at the top, the cylinders are worn tapered! (not perfectly cylindrical any more) Video: Leak Down Testing (user: mycarproject YouTube) NOISES
Adapted from aa1car.com Diagnosing engine noises can be a bit of an art. With experience, and by listening closely to different parts of the engine, you can start to pinpoint where the problems are. A stethescope can be very handy to have, though I just use a screwdriver touch the blade end to what you want to listen to, then touch the handle end against your ear. It's amazing what you can hear in an engine when you listen at specific places. ENGINE CLICKING NOISES A clicking or tapping noise that gets louder when you rev the engine is probably upper valvetrain noise caused by one of three things: low oil pressure, excessive valve lash, or worn or damaged parts. Video: Rocker Noise (user: 98turboteg YouTube) LOW OIL PRESSURE Check the oil level. If it is low, add oil to bring it back up to the full mark. Is the engine still noisy? Check your oil pressure. A low gauge reading (or oil warning light) would indicate a serious internal engine problem that is preventing normal oil pressure from reaching the upper valvetrain components. The cause might be a worn or damaged oil pump, a clogged oil pump pickup screen or a plugged up oil filter. Using too thick a motor oil during cold weather can also slow down the flow of oil to the upper valvetrain, causing noise and wear. Video: Rod Knock (user: MindzEye03rd YouTube) VALVE LASH NOISE Too much space between the tips of the rocker arms and valve stems can make the valvetrain noisy and possibly cause accelerated wear of both parts. COLLAPSED LIFTER NOISE Hydraulic lifters take care of valve lash for you automatically using oil pressure, unless they have
"collapsed." A collapsed lifter will allow excessive valve lash and noise. DAMAGED ENGINE PARTS NOISE Inspect the valvetrain components. Excessive wear on the ends of the rocker arms, cam followers (overhead cam engines) and/or valve stems can open up the valve lash and cause noise. So too can a bent pushrod or a broken valve spring. RAPPING OR DEEP KNOCKING ENGINE SOUND Usually bad news. A deep rapping noise from the engine is usually "rod knock," a condition brought on by extreme bearing wear or damage. If the rod bearings are worn or loose enough to make a dull, hammering noise, you're driving on borrowed time. Sooner or later one of the bearings will fail, and when it does one of two things will happen: the bearing will seize and lock up the engine, or it will attempt to seize and break a rod. Either way your engine will suffer major damage and have to be rebuilt or replaced. Bearing noise is not unusual in high mileage engines as well as those that have been neglected and have not had the oil and filter changed regularly. It can also be caused by low oil pressure, using too light a viscosity oil, oil breakdown, dirty oil or dirt in the crankcase, excessive blowby from worn rings and/or cylinders (gasoline dilutes and thins the oil), incorrect engine assembly (bearings too loose), loose or broken connecting rod bolts, or abusive driving. Video: Piston Slap (diesel engine) (user: om616912 YouTube) Video: Piston Slap 2 (the cause) (user: om616912 YouTube) Bearing wear can be checked by dropping the oil pan and inspecting the rod and main bearings. If the bearings are badly worn, damaged or loose, replacing the bearings may buy you some time. But if the bearings are badly worn or damaged, the crankshaft will probably have to be resurfaced which means a
complete engine overhaul or replacing the engine is the vehicle is worth the expense. ENGINE PINGS OR KNOCKS WHEN ACCELERATING The cause here may be Spark Knock (Detonation) caused by an inoperative EGR valve, overadvanced ignition timing, engine overheating, carbon buildup in the combustion chambers, or low octane fuel. Video: Wrist Pin Knock (user: corvette6698512 YouTube) ENGINE REMOVAL Once an engine has been tested and condemned, it needs to be removed and readied for rebuilding. It's never fun to work on a greasy grimy engine, so we need to clean all the crud off so we don't have to get filthy working on it. Pressure Washing Use plastic bags to cover electrical components and the carburettor or throttle body Spray the entire engine thoroughly with Engine Degreaser (you will likely need at least two cans) Allow to soak Pressure Wash the engine thoroughly WEAR A FACE SHIELD! Do not direct the pressure washer onto
paint, or anything electrical Because the the Face Shield is your best friend don't do the Safety Squint like the guy below Video: Clean Engine (user: ehow YouTube)
Engine Removal In removing the engine, it is very important that you can follow these tips to help ensure success: Label Everything: Don't rely on your memory, tag stuff with masking tape and felt pens. Make it EASY to figure out what goes where. Take pictures if you can! Follow the Manual: The manual tells you and shows you HOW things come apart and go together. Students often refuse to use this valuable resource, and then turn good parts into garbage. Don't be a statistic READ! Organize your Parts: DO NOT lay them out in some sort of order in the shop stuff gets bumped, moved, or borrowed if it's sitting out in the open. I like to use ZipLock bags for my projects it's easy to write on the bag what is inside. Thread fasteners BACK into the holes they came out of. An engine crane (also called a Cherry Picker) I cannot stress enough, the importance of organization!!! This list is pretty general, and is there really to open your eyes to what is involved. Every vehicle will have a slightly different list, but for the most part this works: 1. Disconnect and remove the battery 2. Remove the engine hood 3. Drain the engine coolant, and remove the radiator 4. Drain the engine oil An engine stand 5. Disconnect and label all coolant hoses 6. Disconnect and label all electrical wires 7. Disconnect and label all vacuum hoses 8. Disconnect the air conditioning pump from the motor and lay to the side (do not disconnect the A/C lines) 9. Disconnect the power steering pump from
the motor and lay to the side (do not disconnect the P/S lines) 10. Disconnect the throttle cable, cruise control cable, and automatic transmission linkages from the motor 11. Disconnect the exhaust pipes from the exhaust manifolds 12. Disconnect the torque convertor from the engine flex plate (if automatic) 13. Attach a chain to the motor, using existing bolts or hooks, attach the chain to the engine crane 14. Unbolt the transmission bellhousing from the motor 15. Unbolt the engine motor mounts (you may need to support the engine with the crane) Video: Remove Engine (user: ElectricMgMidget YouTube) 16. Raise the engine, jockeying it around until it clears everything, and remove from the vehicle 17. NEVER leave an engine hangin off the chain put it on the ground, or on an engine stand. SHOW Engine Failure The Twisted World of Mr. Wellwood