4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

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LUBRICATION SYSTEMS The lubrication system used with all Tecumseh horizontal crankshaft engines covered in this manual utilize a splash type system. An oil dipper on the connecting rod splashes oil in the crankcase to lubricate all internal moving parts. The oil dipper is either bolted on or may be cast on to the cap with one of the rod bolts (diag. 6). All vertical shaft engines use a positive displacement plunger oil pump or a rotary oil pump. Oil is pumped from the bottom of the crankcase, up through the camshaft and over to the top main bearing. Oil under pressure lubricates the top crankshaft main bearing and camshaft upper bearing (diag. 7). A crankshaft drilling also provides oil to the crankpin journal on engine models OHV 13.5 -16.5. On all Tecumseh vertical shaft 4-cycle engines, the oil is sprayed out under pressure through a small hole between the top camshaft and crankshaft bearing to lubricate the piston, connecting rod, and other internal parts (diag. 5). The plunger style oil pump is located on an eccentric on the camshaft. As the camshaft rotates, the eccentric moves the barrel back and forth on the plunger forcing oil through the hole in the center of the camshaft. The ball on the end of the plunger is anchored in a recess in the cylinder flange (diag. 8). SPRAY MIST HOLE CRANKCASE PASSAGE PLUG CAMSHAFT DRILLED CAMSHAFT PASSAGE DIPPER 6 MAIN BEARING OIL GROOVE BARREL TYPE LUBRICATION PUMP CRANKSHAFT OIL PASSAGE ASSEMBLE PUMP HOUSING WITH INSIDE CHAMFER TOWARD CAMSHAFT GEAR 7 The rotary pump is driven by the camshaft. It uses a lobed gear in a rotating ring to provide positive oil displacement (diag. 9). SPRAY MIST HOLE FLAT 8 OIL DRAIN HOLE COUNTERBALANCE SYSTEMS Some Tecumseh engines may be equipped with an Ultra-Balance ® counterbalance system. This system uses a single weighted shaft that is driven off the crankshaft. This shaft's function is to counteract the imbalance caused by the counterweights on the crankshaft (diag. 10). A dual shaft counterbalance is also used on some engine models. A gear on the crankshaft drives the counterbalance with the thicker gear, which in turn drives the second counter balance shaft. For timing of either counterbalance system, see " Engine Assembly Procedure " in the Service section of this CAMSHAFT chapter. Not For Resale 5 NOTE: INSTALL OIL PUMP AFTER THE SUMP IS ON DRIVE GEAR www.SmallEngineDiscount.com COUNTER- BALANCE SHAFT GOVERNOR FLANGE 9 10 59
COMPONENTS The cylinder block houses the piston, crankshaft, and along with the cylinder cover all the internal components. The block is a one piece diecast aluminum alloy cylinder casting which may have a cast iron liner (diag. 10). The piston transmits the force of the burning and expanding gases through the connecting rod to the crankshaft. The piston rings provide the seal between the cylinder wall and the piston. The rings keep the combustion pressures from entering the crankcase and also wipe the oil off the cylinder wall and return it to the sump. The connecting rod assembly is the link between the piston (piston pin) and the crankshaft. The cylinder head is a one piece aluminum alloy casting that is bolted to the top of the cylinder block. The overhead design contains all of the valve train except for the camshaft, lifters, and push rods. The crankshaft converts the up and down piston movement to the rotational force (torque) by an offset crankpin or rod journal. The camshaft lobes push the lifters at the proper time to allow air and fuel in and exhaust out of the cylinder. Teeth on the camshaft gear time the camshaft to the crankshaft. The valves allow air-fuel mixture to enter the cylinder and exhaust gases to exit. The valves provide a positive seal when closed. The valve springs return the valves to the closed position and must be strong enough to maintain valve lifter and cam lobe contact. The valve retainers lock the spring to the valve stem. The valve lifters maintain contact on the camshaft, move the push rods to pivot the rocker arms and move the valves. The crankcase breather is a one way check valve that allows air out and prevents air from coming in. It allows the engine to develop a partial vacuum in the crankcase during operation. The cylinder cover provides the bearing surface for the power take off (P.T.O.) end of the crankshaft and camshaft. This bolted on cover is removed to provide access to all internal components. The oil pump (vertical shaft only) consists of a steel plunger and a nylon or aluminum housing that rides an offset on the camshaft. The rotary pump consists of a lobed gear in a rotating ring that is driven by the camshaft. The flywheel provides the mass to smooth the effects of one power stroke every other crankshaft revolution. Flywheels are made of aluminum alloy or cast iron. The flywheel fins act as a fan to cool the engine. CHAMPFER UP TOWARD CAM SHAFT ROTOR OIL SEAL REMOVED PUSH ROD GUIDE PLATE PUSHRODS RING ROTARY PUMP SNAP RING LIFTERS CAMSHAFT VALVES 60 CRANKCASE BREATHER CRANKSHAFT FLYWHEEL Not For Resale www.SmallEngineDiscount.com 10
Page 1 and 2:
Not For Resale www.SmallEngineDisco
Page 3 and 4:
Page TESTING PROCEDURE ............
Page 5 and 6:
SHORT BLOCKS SBV OR SBH IDENTIFICAT
Page 7 and 8:
STORAGE (IF THE ENGINE IS TO BE UNU
Page 9 and 10:
TROUBLESHOOTING OR TESTING If the e
Page 11 and 12: 8 CHAPTER 3 CARBURETORS AND FUEL SY
Page 13 and 14: CARBURETOR VISUAL IDENTIFICATION Se
Page 15 and 16: TESTING 12 1. After repeated effort
Page 17 and 18: If further adjustment is required,
Page 19 and 20: FLOAT ADJUSTING PROCEDURE All Tecum
Page 21 and 22: ASSEMBLY PROCEDURE Welch Plugs To i
Page 23 and 24: Inlet Needle and Seat Make sure the
Page 25 and 26: 22 CHAPTER 4 GOVERNORS AND LINKAGE
Page 27 and 28: Governor Shaft Replacement, Retaini
Page 29 and 30: NOTE: Early production OHH engines
Page 31 and 32: OVM, OVXL, OHV VERTICAL SPEED CONTR
Page 33 and 34: CAUTION: HANDLE MATCHES SAFELY TO A
Page 35 and 36: 32 4. Use a small Phillips screwdri
Page 37 and 38: Stylized Starter (OHV 13.5 -17) 34
Page 39 and 40: CONVERTING ALTERNATING CURRENT TO D
Page 41 and 42: TROUBLESHOOTING ELECTRICAL STARTER
Page 43 and 44: TESTING PROCEDURE STARTING CIRCUIT
Page 45 and 46: 3 AMP DC ALTERNATOR SYSTEM - DIODE
Page 47 and 48: CHECKING THE SYSTEM: To check the s
Page 49 and 50: 10 Amp A.C. Alternator CHECKING THE
Page 51 and 52: LOW OIL PRESSURE SENSOR Test the se
Page 53 and 54: CHAPTER 7 FLYWHEEL BRAKE SYSTEMS GE
Page 55 and 56: BRAKE BRACKET ASSEMBLY Late product
Page 57 and 58: The flywheel with magnets provide t
Page 59 and 60: SERVICE To remove the ignition modu
Page 61: CHAPTER 9 INTERNAL ENGINE AND CYLIN
Page 65 and 66: ENGINE OPERATION PROBLEMS ENGINE MI
Page 67 and 68: ENGINE VIBRATES EXCESSIVELY 64 1. R
Page 69 and 70: 10. Remove the flywheel key and alt
Page 71 and 72: CYLINDERS Visually check the cylind
Page 73 and 74: PISTONS, RINGS, AND CONNECTING RODS
Page 75 and 76: Mechanical Compression Release (MCR
Page 77 and 78: CRANKCASE BREATHERS The breather el
Page 79 and 80: SERVICE BUSHING We are supplying th
Page 81 and 82: 8. Mount the cylinder cover or flan
Page 83 and 84: 13. On engine models OHH and OVRM,
Page 85 and 86: 22. Attach the fuel tank (if applic
Page 87 and 88: 84 ENGINE SPECIFICATIONS OVRM40 OVR
Page 89 and 90: OVERHEAD VALVE TORQUE SPECIFICATION
Page 91 and 92: CHAPTER 11. EDUCATIONAL MATERIALS A
Page 93 and 94: OIL SEAL DRIVER OIL SEAL REMOVER No
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4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

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