HOW TO DISASSEMBLE A FOUR-STROKE ENGINE

IN THIS SECTION, YOU WILL FIND THE FOLLOWING SUBSECTIONS:

THE BASIC DISASSEMBLY PROCEDURE
DISASSEMBLING A FOUR STROKE TECUMSEH ENGINE
STEP 1: DISCONNECT THE SPARK PLUG
STEP 2: DOCUMENT THE ENGINE INFORMATION
STEP 3: DRAIN ALL FLUIDS
STEP 4: CLEAN THE ENGINE EXTERIOR
STEP 5: REMOVE THE SPARK PLUG
STEP 6: REMOVE THE AIR CLEANER
STEP 7: REMOVE THE FUEL TANK AND FUEL LINE
STEP 8: REMOVE THE MUFFLER
STEP 9: REMOVE THE BLOWER HOUSING AND STARTER ASSEMBLY
STEP 10: REMOVE THE CARBURETOR
STEP 11: REMOVE THE IGNITION SYSTEM
STEP 12: REMOVE THE FLYWHEEL
STEP 13: REMOVE THE CYLINDER HEAD
STEP 14: REMOVE THE VALVES
STEP 15: REMOVE THE CRANKCASE COVER
STEP 16: REMOVE THE OIL PUMP
STEP 17: REMOVE THE CAMSHAFT AND THE VALVE LIFTERS
STEP 18: REMOVE THE PISTON AND CONNECTING ROD ASSEMBLY
STEP 19: REMOVE THE CRANKSHAFT
STEP 20: REMOVE ANY BEARINGS OR SEALS
DISASSEMBLING A BRIGGS & STRATTON FOUR STROKE ENGINE

THE BASIC DISASSEMBLY PROCEDURE

Most engines are disassembled using similar procedures. Here is a decent 20 step process whereby you can take apart virtually any four stroke engine, whether said engine is an old L head like the example we provide below, or an overhead valve(OHV) or overhead cam(OHC) model. Because there are slight differences between engines, it may be advantageous to juggle the order of some steps. Never be afraid to do so.

The biggest differences between an L head and an OHV motor is in the positioning of the valves, making valve extraction a bit different. The camshaft will be positioned similarly in the crankcase in both these engines. The valves of an OHC engine will be positioned like those of an OHV engine; however the camshaft will be located in the cylinder head rather than the crankcase, and its rotation by the crankshaft will be done via a timing chain instead of intermeshed gears. While each of these engine configurations is unique in its way, none is significantly more complicated to disassemble or work on than the others. Here is our 20 step disassembly procedure:

1)Disconnect spark plug wire and remove the engine from its equipment
2)Document engine information
3)Drain fluids from the engine
4)Thoroughly clean the engine exterior of dirt, grease, and debris
5)Remove the spark plug
6)Remove the air cleaner
7)Remove the fuel tank and disconnect the fuel line
8)Remove the muffler
9)Remove the blower housing and starter assembly
10)Disconnect linkages and springs from the carburetor; remove the carburetor
11)Remove the ignition coil or electronic ignition system
12)Remove the flywheel
13)Remove the cylinder head
14)Remove the valves, valve springs, and valve spring retainers
15)Remove the crankcase cover
16)Remove the oil pump
17)Remove the camshaft and valve lifters
18)Disconnect the connecting rod from the crankshaft; remove the piston and connecting rod assembly from the block
19)Remove the crankshaft
20)Remove any bearings or seals in the crankcase

DISASSEMBLING A FOUR STROKE TECUMSEH ENGINE

Following are the above 20 steps applied to an 3.5 horsepower L head Tecumseh motor with recoil start, a vertical crankshaft, and electronic ignition.

STEP 1: DISCONNECT THE SPARK PLUG
(Will be performed the same way on L head, OHV, OHC motors)

Before beginning work, disconnect the spark plug wire. Since most small engines run with no outside power sources(like a battery), they can start unexpectedly as they are being worked on. To ensure that this does not happen, you should ground the disconnected spark plug wire by fastening it to the engine block. On many engines, a grounding stub will be located near the spark plug wire.

STEP 2: DOCUMENT THE ENGINE INFORMATION
(Will be performed the same way on L head, OHV, OHC motors)

Document all engine information. You will need the engine identification number when you are ordering parts, or looking up specifications in your service manual. Write down the information for speedy reference. The example engine is a Tecumseh Legend with 3.5 horsepower, electronic ignition, and oil pump lubrication.

STEP 3: DRAIN ALL FLUIDS
(Will be performed the same way on L head, OHV, OHC motors)

Drain all fluids from the engine. To drain the gasoline, disconnect the fuel line, remove the filler cap on the fuel tank, and turn the engine upside down so that fuel can run into a secure container. To remove the engine oil, take out the oil drain plug, and drain the oil into an approved container. Remember to follow appropriate disposal procedures(the easiest disposal method is to take the used oil to Checker Auto or Autozone).

STEP 4: CLEAN THE ENGINE EXTERIOR
(Will be performed the same way on L head, OHV, OHC motors)

Once the fluids have been drained, the engine should be cleaned. Cleaning an engine prior to disassembly makes it easier to locate fasteners, and also to remove them.

STEP 5: REMOVE THE SPARK PLUG
(Will be performed the same way on L head, OHV, OHC motors)

Always use a spark plug socket to remove the plug. Using a plug socket instead of some alternative implement will prevent damage to the plug insulator. Fit the socket over the spark plug terminal, and loosen it until the plug can be removed by hand.

STEP 6: REMOVE THE AIR CLEANER
(Will be performed the same way on L head, OHV, OHC motors)

To remove the air cleaner, you will probably need to remove the cover on the air cleaner housing. After this been accomplished, remove the air cleaner filter element. In this Tecumseh engine, it is a piece of foam rubber. Without the filament in the way, the fasteners securing the main air cleaner housing can be accessed. On the Tecumseh motor, two screws attach the housing to the carburetor, when these are removed, the housing is free.

STEP 7: REMOVE THE FUEL TANK AND FUEL LINE
(Will be performed the same way on L head, OHV, OHC motors)

On this Tecumseh, the oil dip stick tube runs up through the fuel tank. For this reason, the dipstick must be removed from its tube before you can proceed. After removing the dipstick, the three retaining bolts on the fuel tank surface can be extracted. Disconnect the fuel line that runs between the tank and carburetor. Since the tank has already been emptied, no fuel should leak out.

With the fuel tank out of the way, you will be able to see the dipstick tube that extends from the base of the crankcase. The tube is fastened to the side of the engine by just one bolt. After this bolt has been loosened, the tube can be lifted out of the crankcase. In this case, there is an O ring seal at the bottom of the tube which prevents oil leaks from the tube bottom where it fits into the crankcase. When the dipstick tube is removed, this seal may come out with it, or it may remain in the crankcase hole. If an O ring seal stays inside of a hole this way, try using a pair of needlenose pliers or a small screwdriver to dig it out.

STEP 8: REMOVE THE MUFFLER
(Will be performed the same way on L head, OHV, OHC motors)

The muffler housing on this Tecumseh engine is secured to the block with two bolts. Bolts that secure a muffler can become corroded or rusted into place, and therefore their removal might require extra force. Be cautious not to break these bolts. Use the proper sized tool, and if possible, a six point socket or six point wrench. This will help prevent tool slippage, and rounded bolt heads. When loosening a bolt that is stuck in place by rust or corrosion, consider soaking its threads with a lubricant like WD-40 in advance.

STEP 9: REMOVE THE BLOWER HOUSING AND STARTER ASSEMBLY
(Will be performed the same way on L head, OHV, OHC motors)

At this juncture, most of the external engine items should have been removed. The only external parts that remain are the blower housing and carburetor. The blower housing controls the flow of air across the engine for cooling as it operates. In this Tecumseh engine, the flywheel is positioned directly beneath the blower housing. As the flywheel spins, its fins act like fan blades and propel air over the engine.

This engine is like many in that the starter assembly attaches to the blower housing, and will therefore come off as one entity. Four bolts hold the housing in place on the Tecumseh. Once these bolts are removed, you can lift the housing from the engine. This leaves visible the flywheel and ignition system.

If there is a problem with the starter assembly, it can be separated from the blower housing for repair. A recoil start assembly relies on a coiled spring to retract the recoil rope each time it is pulled. Be aware that this recoil spring is under tension, so as you draw the starter assembly from the blower housing point it away from yourself and other persons to avoid injury via an uncoiling recoil spring.

STEP 10: REMOVE THE CARBURETOR
(Will be performed the same way on L head, OHV, OHC motors)

The Tecumseh engine uses a float type carburetor. There is linkage and a spring that attaches the throttle control bracket of the carburetor to the speed governor. The throttle control bracket is a metal plate secured to the intake manifold by two bolts. With these removed, the bracket can be lifted up to expose the governor linkage and spring connections on its underside.

Before you disconnect this linkage and spring, their proper positions should be noted carefully. Here is where you will want to either enact a quick sketch, or take some photographs to record the placement of these small components. It is appallingly easy to forget how these are connected, and an engine will never run right if they are reconnected incorrectly. So after you have recorded the linkage and spring positions, they can be disconnected. On this particular engine, there is also a kill wire attached to the throttle control bracket; this wire must be connected to the ignition system for the engine to shut down when its throttle is moved to the OFF position. This kill wire, like the governor linkage and spring, must be documented before it is unhooked. With all of these small components detached from the throttle control bracket, the bracket itself is free from the engine.

With the throttle control bracket out of the way, the carburetor and intake manifold can be removed from the engine as one assembly. This Tecumseh engine utilizes two bolts to secure its intake manifold to its block. There are no fasteners between the carburetor and block, so as the intake manifold bolts come out, you will need to support the carburetor to keep it from dropping to the floor and sustaining damage.

When you are removing the carburetor, try to keep it in an upright position. Unless you ran the engine dry prior to pulling it from the piece of equipment, there will be fuel remaining in the carburetor float bowl. Keeping it upright means not spilling. After the carburetor has been removed from the engine, you can invert it to drain the remaining fuel from the bowl.

Be aware that dissecting a carburetor during a rebuild is not usually necessary. If the carburetor appeared to be working, it should be left intact and set aside for eventual reassembly.

STEP 11: REMOVE THE IGNITION SYSTEM
(Will be performed the same way on L head, OHV, OHC motors)

Our Tecumseh engine employs an electronic ignition system. Electronic modules are frequently mounted at the outside edge of a flywheel, and therefore should be removed prior to the flywheel.

Removing an electronic ignition module is an easy process. You would simply remove the bolts holding the module in place. Being that it is one of the flimsier and more fragile engine parts, take care that it does not drop to the floor, and store it in a protective manner that prevents it from being damaged.

STEP 12: REMOVE THE FLYWHEEL
(Will be performed the same way on L head, OHV, OHC motors)

The flywheel contains permanent magnets that energize the ignition coil as the flywheel rotates. The flywheel is also used to smooth out the jerky pulses of the crankshaft as it turns. In a four stroke engine, the crankshaft turns with every other piston stroke, and the weight of the flywheel helps maintain a consistent turning speed in the crankshaft in between these dominant piston strokes.

The engine crankshaft has a tapered end. A hole in the center of the flywheel is tapered to match that crankshaft end for a tight fit. The two parts, both tapered, lock themselves together when installed. When the flywheel is installed, the crankshaft end will protrude through it, and a retaining nut attached to keep the two components tightly bound.

A metal key is used to keep the flywheel from rotating on the end of the crankshaft. This flywheel key is a tiny piece of metal that fits into slots in the flywheel and crankshaft end. When the flywheel is being detached from the crankshaft, watch for this key; it is very small, and easily misplaced. Often(but not always) the flywheel key will remain stuck to either the crankshaft or flywheel when these components are separated. Always be sure that, after the flywheel is free, you locate the key, remove it from its slot, and store it in a good safe place.

Now consider how to best get the flywheel off of the crankshaft. First you must loosen the flywheel retaining nut. Since the flywheel turns with the crankshaft, the flywheel crankshaft assembly will also turn when you try to loosen the retaining nut. To prevent the flywheel from turning, you will need to use a tool called a flywheel holder. There are different types of flywheel holders available: one kind uses a strap to harness the outside edge of the flywheel and keep it from rotating; another slides between flywheel fins to prohibit rotation. An service manual will often specify what style flywheel holder to use with a given engine. You may be able to obtain one designed for that engine from the manufacturer. When the flywheel holder is in place, you can remove the flywheel retaining nut and its washer; this Tecumseh engine also possesses a starter cup which can now be withdrawn.

Even with the retaining nut removed, you will discover that the flywheel cannot simply be pulled from the crankshaft. These two components wedge together so tightly that another special tool is needed to separate them. The tool in question will be either a knock off tool or a flywheel puller. As with the flywheel holder, the type of tool required, knock off or flywheel puller, will vary depending on the engine make and model. On our Tecumseh engine, a knock off tool is used. The knock off tool is a threaded piece of aluminum that can be screwed onto the threads of the crankshaft end. Then, to knock the flywheel loose, you would pry up on it from underneath, and when it was loose, drive the crankshaft through it with a hammer. The only purpose of the knock off tool in this case is to protect the end of the crankshaft from direct hammer blows; hammer blows could cause damage to the crankshaft end threads, or mushrooming of the metal crankshaft tip. Either outcome would prevent reinstallation of the flywheel retaining nut later. The aluminum knock off tool, when fitted over the threads, can be hammered on with impunity to thread or crankshaft end damage.

The knock off tool should be threaded just partway onto the crankshaft. If it were to be screwed on too tightly, it would prohibit the flywheel from coming off. With the tool in place, pry up on the flywheel edge from underneath with a pry bar, as the flywheel is loosened by hammer strikes to the end of the puller. Usually one or two blows from a hammer will dislodge the flywheel.

Remember to account for the flywheel key as soon as the flywheel is removed. Place it where it will be protected and not lost.

STEP 13: REMOVE THE CYLINDER HEAD

L Head

In an L head motor, to detach the cylinder head you must remove the bolts securing it to the block. Try to loosen the bolts evenly, each one a few turns at time, and begin with any at the corners of the head before proceeding to those in the center. Loosening bolts in this way will lessen the chance of cylinder head warping or bending.

The cylinder head in the Tecumseh engine is secured by eight bolts. With these removed, the head can be lifted from the engine block, and the old cylinder head gasket extracted. During disassembly, you should never be concerned about damaging a gasket; they will always be replaced during reassembly. In fact, the old gasket should be replaced whenever a cylinder head is removed. If any of the gasket material remains on the cylinder block or head, it will need to be scraped away with a putty knife.

Overhead Valve or OHV

The cylinder head in an overhead valve engine will be guarded by a head cover; remove this first, along with the cover gasket. With this cover extracted, you will see the rocker arms that activate the engine valves. The valve heads will be visible on the underside of the cylinder head after it has been removed.

NOTE: before removing the cylinder head, some manufacturers recommend that the piston be positioned at top dead center(TDC) of its compression stroke; this is so that both valves will be closed when the cylinder head is removed. You can move the piston by rotating the crankshaft by hand, the ends of which should be protruding from the crankcase. Since by now, the engine oil has been drained, you can dispense a teaspoonful or so of new oil into the spark plug hole to help lubricate the cylinder walls as the piston is moving. With the cylinder head cover removed, leaving the rocker arms visible, it will be easy to see when both valves are in their closed positions; TDC on the piston compression stroke will occur when neither rocker arm is exerting downward pressure on its valve stem.

When the piston is positioned appropriately, the rocker arms should no longer be needed; however, unbolting them at this time is not required unless they are obstructing your access to the cylinder head bolts. If such access is not hindered, rocker arm removal can be accomplished later, when the valves themselves are pulled from the freed up cylinder head. Depending on the engine, there can be as few as two, or as many as four, bolts mating the cylinder head and engine block. Extract these, and the cylinder head assembly will be liberated. With it out of the way, you will see the push rods protruding from the engine block; go ahead and remove these at this stage. Lingering cylinder head gasket material can be scraped from the head or engine block with a putty knife.

NOTE: that engine manufacturers will recommend that the piston be at top dead center(TDC) on its compression stroke before the cylinder head is removed.

Overhead Cam or OHC

STEP 14: REMOVE THE VALVES

What remains with the cylinder head removed is the lower end of the engine. This, the cylinder and crankcase together, is referred to as a short block. If you were to purchase a new short block assembly, this is what you would receive. Be aware that the short block may not include valve assemblies in an OHV or OHC powerplant(or a camshaft and timing chain in an OHC motor). Be certain that you know what is included in a short block package before purchase.

L Head

Now you can turn your attention to removing the valves. Begin by removing the valve cover, a thin plate of aluminum that shields the area in the engine block which houses the valves. The valve cover of our Tecumseh engine is positioned perpendicular to the crankshaft and immediately beneath the intake and exhaust ports. This particular valve cover is held in place by two bolts. When the valve cover has been removed, the intake and exhaust valves and their valve springs will be visible.

These springs apply pressure to the intake and exhaust valves, keeping them firmly closed until the camshaft is in position to heave them open. Each valve spring is held in place by a small retainer which slides into a groove on the valve stem. For the retainer to be either removed or inserted, the valve spring in question must be compressed so that spring pressure on the retainer is relieved.

The valve springs will be squeezed by a tool known as a valve spring compressor. The tool is a small clamp that can be fitted over the spring ends as they sit inside the engine. Tightening the clamp compresses the valve spring, and allows the retainer to be drawn over the end of the valve stem. Begin with either spring you chose; the order of removal does not matter.

The retainer must first slide horizontally so that the wider section of its slot is centered on the valve stem. The retainer slot is comprised of two overlapping holes, one larger than the other. The smaller of these holes conforms in size to the groove on the valve stem, while the larger is a size or two bigger than the standard stem circumference. When the retainer has ceased to hold the spring and valve together, the valve can be pulled from the top of the cylinder, and the spring itself removed inside the compressor tool. Keep in mind that the spring remains under extreme pressure; pressure on the spring should be released slowly to prevent it soaring from the tool jaws.

Overhead Valve or OHV

Your cylinder head, containing its valves, has been separated from the engine block. In order to extract the valves, you will need to reach the valve springs. Therefore, if the rocker arms were not removed before, do it now. Each rocker arm will be held in place by a locknut, and beneath the locknut a threaded adjuster. With these taken off, the rocker arm will come free.

To free the valve, the spring must first be compressed. This requires a slightly different compression tool than the one employed above on the L head valve springs. Though it may vary by engine, the tool is probably a standard looking clamp; its stationary end will be braced by the underside of the cylinder head, while its movable end is tightened to apply pressure to the spring. Try to compress the valve spring only as much as it takes to remove the retainer clip from the valve stem groove. Beneath the clip will be a valve spring retainer which should slide off uninhibited. At this point, the valve is free; however, the compression tool remains positioned on the valve spring. Slowly loosen the valve spring compressor until it has released its pressure on the spring. By relieving the pressure slowly, you can avoid the spring escaping and possibly injuring somebody.

Overhead Cam or OHC

STEP 15: REMOVE THE CRANKCASE COVER
(Will be performed the same way on L head, OHV, OHC motors)

To access the components inside the crankcase, you must remove the crankcase cover. If the engine, like this Tecumseh, harbors a vertical shaft, the crankcase cover will be located at the bottom of the engine. If an engine possesses a horizontal crankshaft, the crankcase cover will be located at the left or right edge of the crankcase. Your engine service manual may refer to the crankcase cover as a sump or sump cover.

On the Tecumseh, six bolts secure the crankcase cover to the crankcase. There will be a gasket between the crankcase cover and crankcase to prevent oil leakage. Remove any lingering gasket residue with a putty knife. When the crankcase cover is pulled from the engine, you will notice that there are steel dowel pins between the surfaces to preserve their precise alignment. These small pins are referred to as alignment dowels; they are inserted into matching holes in the crankcase and crankcase cover. Since one crankshaft bearing is located in the cover, and the other in the crankcase itself, their correct alignment is critical for proper crankshaft rotation. The Tecumseh engine has just two alignment dowels between its crankcase and crankcase cover. Often a small engine will have more.

Because dowels are simply inserted into drilled holes(instead of being fastened), you should be able to pull them out. Be on the alert for alignment dowels as you pull the crankcase cover from the crankcase. Also keep in mind that, during engine reassembly, the dowels must be replaced.

STEP 16: REMOVE THE OIL PUMP
(Will be performed the same way on L head, OHV, OHC motors)

After the crankcase cover has been removed, you will be able to observe the engine oil pump. Oil pumps in small engines are almost always puny innocuous looking things that look, if anything, inadequate for their purpose; actually they work quite well(LUBRICATION SYSTEMS). In the Tecumseh, the oil pump is a small plastic affair that contains a metal rod that ends in a tiny ball. The plastic part of the pump is forced up and down by the camshaft. As it slides along the metal rod, a pumping action ensues, causing oil to be spread over and onto engine components.

With this engine, the primary thing to be cognizant of is that upon reassembly, the ball end of the metal rod must fit into a crankcase cover cavity designed for it; if it is not properly placed, the pump will not work, and oil will not reach the engine components it needs to. The same is true regardless of pump type. Another engine may use a gear driven pump, or a simple slinger that dips into the oil reservoir at the bottom of the engine as the crankshaft rotates, and splashes oil across engine components. The oil pump is a small but exceedingly important engine component that must always function properly, and be installed properly.

To remove the Tecumseh oil pump, you would just slide it off of the camshaft. It may be desirable to first pull the metal rod from the pump to prevent damage. If an engine contains a mechanical speed governor, like this Tecumseh, it will likely be visible on the inside surface of the crankcase cover. A mechanical governor operates on the basis of centrifugal force. It will contain a gear whose teeth mesh with the teeth of either a camshaft or crankshaft gear. As engine speed increases, the cam or crankshaft gear spins the governor gear at an accelerated pace; this causes a pair of weights attached to the governor gear to swing outward, drawing a governor plate against a lever that, through a system or springs and linkage, influences engine speed at the carburetor.

This particular engine is similar to many in that its governor cannot be removed or installed easily. As long as the governor functioned effectively before the engine was disassembled, and if it appears to be in good condition after a careful visual examination, then it should not be removed.

STEP 17: REMOVE THE CAMSHAFT AND THE VALVE LIFTERS

L Head and Overhead Valve or OHV

If you are working on one of these engines, you will be able to see a pair of intermeshing gears inside the crankcase with the crankcase cover removed. A gear on the crankshaft is mated to larger gear on the camshaft. The camshafts in L head and OHV engines will be positioned similarly in the crankcase.

Both the crankshaft and camshaft gears will be endowed with punch marks which need to be aligned when the engine is reassembled to ensure that the valves open and close at proper intervals. To remove the camshaft in an L head engine, the timing marks on the gears should be aligned(should not be necessary in an OHV powerplant). Rotate the L head camshaft until the punch marks line up. This guarantees that there will be no load on the cam as it is removed. With the valves previously extracted, load on the camshaft will be minimized, however it still makes sense to have the marks aligned. Most of the time, timing marks on the intermeshing crankshaft and camshaft gears are designed to line up when the piston reaches top dead center or TDC on the engine compression stroke. At this point, the cam lobes will not be activating the valve lifters, making it that much easier to remove the cam from the crankcase.

With the camshaft withdrawn, you will perceive above where it was positioned two metal rods with wide flat ends; they will be stretching downward from the top of the engine block. These are the valve lifters or tappets. The wide flat end surface of the valve lifter is what contacts the camshaft lobe. In an L head motor, the opposing end of the lifter will press against the valve stem; in an OHV engine, it will press against a pushrod which, in turn, pushes on a rocker arm to open the valve. In either engine configuration, the valve lifter will stimulate an opening of the valve whenever the oblong side of the cam lobe rotates against it. There will be two lifters in a single cylinder L head or OHV engine, one for each valve; with the camshaft removed, they should be easy to pull out.

Overhead Cam of OHC

STEP 18: REMOVE THE PISTON AND CONNECTING ROD ASSEMBLY
(Will be performed the same way on L head, OHV, OHC motors)

As of now, the only parts remaining inside the engine are the crankshaft, and the piston and connecting rod assembly. The Tecumseh engine contains a two piece connecting rod. The bottom end of the rod is called the rod cap. The two parts of the connecting rod are bolted around the crankshaft crankpin.

To remove the piston and rod, the connecting rod cap must come off first. Removing the cap will allow you to disconnect the rod from the crankshaft, after which the piston and rod assembly can then be extracted together through the top of the cylinder. There are two bolts securing the rod cap to the main connecting rod in this Tecumseh engine. Since it is important during reassembly to replace these bolts in the positions from which they were removed, be sure to keep them separate from other engine bolts. After these two bolts have been removed, the rod cap should come free.

There will probably be no discernible difference between the two sides of the end cap. Therefore consider making a small mark on the cap and main connecting rod with a punch or scribe so that the cap is not reinstalled backward. Installing a cap backward should not affect engine operation; however these parts, worn in together, will fit together better during reassembly if they retain their original positions.

Before you remove the piston, observe its installed position. There are two ways to install a piston and connecting rod, and on many engines, it will make a difference to engine performance if this assembly is installed backwards. Prior to removing the assembly, mark the piston and take note of its position so that it is reinstalled correctly. A piston can be marked in many ways, but remember that, since these parts will be cleaned before engine reassembly, that a non permanent mark(ink for example) may be unavoidably eradicated. Instead try leaving a small scratch or punch mark in the top of the piston to indicate how the assembly should be replaced in the cylinder. Always be careful though not to impact the area of piston where the rings are installed.

The piston and rod assembly can now be lifted from the cylinder. To do this, rotate the crankshaft so that the piston reaches TDC; ideally it should be flat against the top of the cylinder. Then, using your fingers, reach into the crankcase and push the connecting rod end off of the crankshaft crankpin. This will propel the piston through the top of the cylinder. When the piston protrudes from the cylinder, you can grasp it and pull it out from above.

After removing the assembly, unhook the piston from the connecting rod. Usually the wristpin will be held in place by a retaining clip. Use needlenose pliers to remove this clip, and the wristpin will then slide out of the piston, freeing the connecting rod. The retaining clip that secures the wristpin will only need to be replaced during reassembly if it is in some way defective. Keep the clip in a safe place until you need it later.

STEP 19: REMOVE THE CRANKSHAFT
(Will be performed the same way on L head, OHV, OHC motors)

Now the crankshaft can be pulled from the crankcase. The crankshaft will be supported in the crankcase by a bearing. You should be able to remove it easily enough by simply pulling it from its bearing, however the crankshaft should be handled carefully to guard against damage to it or its bearing.

STEP 20: REMOVE ANY BEARINGS OR SEALS
(Will be performed the same way on L head, OHV, OHC motors)

The final step in the disassembling of an engine is to remove any bearings or seals that are in the crankcase and crankcase cover. This Tecumseh engine has no separate crankshaft bearing. It uses the aluminum crankcase itself as a bearing surface. For suggestions regarding bearing removal, see ENGINE BEARINGS.

What the Tecumseh does possess is a crankcase oil seal. This type of seal prevents oil leakage from the site where the crankshaft exits the crankcase. The oil seals(one for each end of the crankshaft) are pressed into place from outside the crankcase. Oil seals such as these are normally removed with a special tool which resembles a miniature pry bar. The seal remover is used to pry the edges of the seal free. Remember not to worry about seal damage. Oil seals will always be replaced during engine reassembly.

DISASSEMBLING A BRIGGS & STRATTON FOUR STROKE ENGINE

Consider a 3.0 horsepower, L head Briggs & Stratton four stroke engine with a vertical crankshaft. How would you go about its disassembly? You would follow an almost identical procedure to the one applied above to the Tecumseh.

Your preliminary steps before the disassembly procedure commences are the same. They include disconnecting the spark plug wire, noting and recording engine data, cleaning the engine exterior, and draining all engine fluids. The model number on this engine is 92502, the type number is 0773-01, and the code number is 80041424.

You must disconnect the spark plug wire, and ground it against the engine. After you have disconnected the plug wire, the spark plug itself can be removed, however its removal now is not absolutely critical.

Next you would remove the air cleaner, which, on this engine, is attached by a single bolt. Removal of the air cleaner allows the blower housing to be easily accessed. With its pain free access, it will not hurt anything to deviate from the process slightly and pull the blower housing and recoil start assembly from the engine now. This will permit easier access to other engine components. The blower housing can be freed by removing three bolts, and as before, the recoil start, unless dysfunctional, does not need to be detached from the blower housing.

The muffler on this Briggs can be unscrewed from the engine block with a pair of vise grips or channellock pliers. Since the muffler may be difficult to loosen, try wetting its threads first with solvent or lubricant.

The flywheel and ignition coil in this Briggs engine are underneath the blower housing. An air vane governor is used to manage engine speed. An air vane governor is operated by air from the flywheel; a thin flat strip of metal called an air vane captures air currents manufactured by the spinning flywheel. As the engine rotates at a higher rpm, air blown by the flywheel increases accordingly. An increased air flow pushes the air vane away from the flywheel, and it tugs on linkage that in turn closes the carburetor throttle plate. This process keeps the engine from over revving. Likewise, as the engine speed slows, the flow of flywheel induced air decreases, and a spring pulls the air vane closer to the flywheel; it pulls on throttle plate linkage which in turn opens the carburetor throttle plate. This action prevents the engine from stalling.

On the Briggs L head, the carburetor is attached directly to the top of the fuel tank. Because the carburetor sucks fuel straight from the tank, a fuel line between the two is unnecessary. The easiest way to remove these components is to remove the two bolts that hold the fuel tank to the engine, and pull both carburetor and tank away together. As you pull the carburetor tank assembly from the engine, you will need to disconnect the governor linkage from the carburetor. Be sure to note how this linkage is attached so that it can be reinstalled accurately. The Briggs carburetor is held to the fuel tank by a handful of screws. With these withdrawn, the carburetor can be separated from the tank, if necessary. Remembering that unless the carburetor was malfunctioning prior to disassembly, it is as well to leave it alone.

Special tools will be required to remove the engine flywheel. This Briggs engine requires that you utilize a flywheel holder, a flywheel wrench, and a flywheel puller. The flywheel retaining nut is designed to function as a drive for the recoil start. The flywheel holder must be used to hold the flywheel motionless while its retaining nut is removed. The flywheel wrench is the tool that loosens the retaining nut. The flywheel holder needed for this engine is a strap wrench. The strap wrench surrounds the exterior surface of the flywheel rather than slipping between its blades.

After the flywheel retaining nut has been removed, the flywheel can be dislodged with a flywheel puller. This is a different device than the knock off tool employed earlier during disassembly of the Tecumseh engine. The flywheel puller is slipped over the end of the crankshaft. Then two long bolts, each of which has had a nut tightened almost to its head, are placed through holes in the puller surface, through two more nuts below the puller surface, and finally are threaded into matching holes in the flywheel itself. The nuts that rest between the underneath puller surface and the flywheel are tightened against the flywheel surface. Then the nuts resting between the bolt heads and upper puller surface are tightened evenly, one turn at a time, into the tool. This tightening motion causes the flywheel to be drawn upward until it is freed from the crankshaft.

The Briggs engine uses a flywheel magneto ignition system which is located beneath a protective metal cover underneath the flywheel. With both flywheel and protective cover removed, you can observe the points and condenser employed by this elderly engine as a triggering mechanism. To remove the condenser, you must remove a screw and retaining bracket that keep it in place. Before the condenser is lifted out, it needs to be disconnected from other parts of ignition system. This is a matter of detaching one wire. It should be done with a condenser removal tool that depresses the spring holding the wire in place. After the condenser has been liberated, you can also remove the screw that fastens the points to the engine block and remove them.

For the rest of the disassembly, follow the same steps that were used to deconstruct the Tecumseh engine above. Remove the bolts from the cylinder head, and lift it away. On this engine, the carburetor throttle control bracket is mounted to the engine by these same cylinder head bolts; therefore the throttle control bracket will be freed along with the cylinder head. From there, the valves, the valve spring retainers, and the valve springs themselves can be removed.

Next you would remove the crankcase cover to reveal the internal engine components. This Briggs motor has a different oil pump than the one used by the Tecumseh. It is a type of slinger(LUBRICATION SYSTEMS) that resides in oil at the bottom of the crankcase, and is rotated via intermeshing gears by the camshaft. Paddles on the outer edge of the slinger dip into crankcase oil and fling it over engine parts, affording them lubrication as the engine runs. The faster the engine runs, the faster the slinger rotates, and the more lubrication oil it flings.

The Briggs & Stratton engine contains a two piece connecting rod. If the rod cap is unbolted, the piston and main connecting rod can be removed, as with the Tecumseh, through the top of the cylinder. The crankshaft can then be pulled from the crankcase. This engine contains the same kind of crankshaft bearing as the Tecumseh; in other words, the aluminum crankcase itself serves as the crankshaft bearing. Therefore there is no bearing to remove. Also like the Tecumseh, the Briggs engine does use oil seals. For hints regarding seal removal, visit the section on ENGINE BEARINGS.