Yamaha MZ250 Page 73 Service Manual Download

Page: 73 / 118

3-39

ENG

2. Measure:

Piston clearance

Out of specifications

→

Rebore or

replace the cylinder, and then replace
the piston and piston rings.

Piston clearance =
Cylinder inside diameter –
Piston skirt diameter

Piston clearance:
Refer to “SPECIFICATIONS” in

the Supplementary service
manual.

Limit:
Refer to “SPECIFICATIONS” in

the Supplementary service
manual.

PISTON, CAMSHAFT, CRANKCASE, AND

CRANKSHAFT

CHECKING THE PISTON AND PISTON PIN

1. Measure:

Piston skirt diameter

= 10 mm (0.4 in) from the piston

bottom edge

Out of specification

→

Replace.

Piston skirt diameter:
Refer to “SPECIFICATIONS” in

the Supplementary service
manual.

Limit:
Refer to “SPECIFICATIONS” in

the Supplementary service
manual.

307-001

Summary of Contents for MZ250

Page 1: ...MZ250 MZ300 SERVICE MANUAL 7VB F8197 10 LIT 19616 01 80 cover indd 1 2012 10 30 12 01 25 ...

Page 2: ...cover indd 2 2012 10 30 12 01 25 ...

Page 3: ...ions of this manual TIP This Service Manual contains information regarding periodic maintenance to the emission control system Please read this material carefully HOW TO USE THIS MANUAL PARTICULARLY IMPORTANT INFORMATION Particularly important information is distin guished in this manual by the following nota tions This is the safety alert symbol It is used to alert you to potential personal injur...

Page 4: ...ica tions for each model are provided on the Supplementary Service Manual 8 3 21 ENG CYLINDER HEAD COVER CYLINDER HEAD 12 Nm 1 2 m kgf 8 7 ft lbf 50 Nm 5 0 m kgf 36 ft lbf 1st 2nd 6 5 4 3 1 2 7 8 9 9 7 8 7 Nm 0 7 m kgf 5 1 ft lbf 11 Nm 1 1m kgf 8 0 ft lbf 11 Nm 1 1m kgf 8 0 ft lbf 20 Nm 2 0 m kgf 14 ft lbf 2 3 Nm 0 23m kgf 1 7 ft lbf Order Job Parts to remove Q ty Remarks Removing the cylinder hea...

Page 5: ...ts Engine Carburetor Electrical Troubleshooting Specifications Filling fluid Lubricant Special tool T R Tightening torque Wear limit clearance Engine speed Electrical data Replace the part with a new one LS Lithium soap base grease M Molybdenum disulfide grease E Engine oil M Molybdenum disulfide oil LT Apply locking agent LOCTITE ...

Page 6: ......

Page 7: ...INDEX GENERAL INFORMATION GEN INFO PERIODIC CHECKS AND ADJUSTMENTS CHK ADJ ENGINE ENG CARBURETOR ELECTRICAL TROUBLESHOOTING CARB ELEC TRBL 1 2 3 4 5 6 ...

Page 8: ...ADJUSTING THE VALVE CLEARANCE 2 12 ENGINE SPEED WITH THROTTLE LEVER MODEL 2 14 ENGINE SPEED 2 15 ADJUSTING THE ENGINE SPEED WITH THROTTLE LEVER MODEL 2 15 ADJUSTING THE ENGINE SPEED 2 17 RECOIL STARTER 2 17 FITTINGS AND FASTENERS 2 17 CHAPTER 3 ENGINE ENGINE INSPECTION 3 1 MEASURING THE COMPRESSION PRESSURE 3 1 AIR FILTER 3 3 SILENT SEMI DRY TYPE 3 3 SEMI CYCLONE TYPE 3 4 FUEL TANK CANISTER 3 5 CH...

Page 9: ...CKING THE PISTON AND PISTON PIN 3 39 CHECKING THE PISTON RING 3 41 CHECKING THE CRANKSHAFT 3 42 CHECKING THE CONNECTING ROD OIL CLEARANCE 3 44 INSTALLING THE PISTON AND PISTON RING 3 45 INSTALLING THE CRANKSHAFT 3 46 SELECTING THE CRANKSHAFT SHIM P T O SHAFT TYPE E 3 48 CHAPTER 4 CARBURETOR REMOVING THE CARBURETOR 4 1 DISASSEMBLING THE CARBURETOR 4 2 MANUAL CHOKE MODEL 4 2 AUTO CHOKE MODEL 4 3 CHE...

Page 10: ...CHAPTER 6 TROUBLESHOOTING ENGINE 6 1 ...

Page 11: ...oils grease and sealers or the equivalents 3 Expendable parts Always replace the gaskets O rings cotter pins and circlips with new parts when servicing engine 4 Tightening torque Be sure to follow torque specifications When tightening bolts nuts or screws start with the largest diameter fastener and work from an inner position to an outer position in a crisscross pat tern 5 Notes on disassembly an...

Page 12: ...d O rings must be cleaned 2 Properly oil all mating parts and bearings during reassembly Apply grease to the oil seal lips BEARINGS AND OIL SEALS Install the bearing s 1 and oil seal s 2 with their manufacture s marks or numbers facing outward In other words the stamped letters must be on the side exposed to view When installing oil seal s apply a light coating of lightweight lithium base grease t...

Page 13: ...osen or damage the leads a Checking the connections Check the leads couplers and connectors for stains rust mois ture etc 1 Disconnect 9 Lead 9 Coupler 9 Connector NOTICE 9 When disconnecting a coupler release the coupler lock hold both sections of the coupler securely and then dis connect the coupler 9 There are many types of coupler locks therefore be sure to check the type of coupler lock befor...

Page 14: ...on Connect properly TIP 9 If the pin 1 on the terminal is flattened bend it up 9 After disassembling and assembling a coupler pull on the leads to make sure that they are installed securely 4 Connect 9 Lead 9 Coupler 9 Connector TIP 9 When connecting a coupler or connector push both sections of the coupler or connector together until they are connected securely 9 Make sure all connections are tigh...

Page 15: ...log pocket tester YU 03112 C Pocket tester 90890 03112 TIP 9 If there is no continuity clean the terminals 9 When checking the wire harness perform steps 1 to 4 9 As a quick remedy use a contact revitalizer available at most part stores BASIC SERVICE INFORMATION ...

Page 16: ... gauge P N 90890 03180 This gauge is used to adjust valve clearance piston clearance and piston ring end gap 4 Digital tachometer P N YU 39951 B 90890 06760 This tool is needed for observing engine r min 5 Engine compression tester P N YU 33223 Compression gauge P N 90890 03081 This tool is used for checking engine compression ø9 ø8 ø10 ø3 ø4 YM A5970 3 Six piece tappet set P N YM A5970 Tappet adj...

Page 17: ...lder P N YS 01880 A Sheave holder P N 90890 01701 This tool is necessary for holding the magneto rotor SVU1220 8 Heavy duty puller P N YU 33270 B Flywheel puller P N 90890 01362 This tool is necessary for removing the magneto rotor 9 Valve spring compressor P N 90890 01253 This tool is used to remove the valve springs 13 Oppama pet 4000 spark checker P N YM 34487 Ignition checker 90890 06754 This ...

Page 18: ...l These controls not only function to ensure air filter but are also vital to proper engine operation and maximum performance PERIODIC MAINTENANCE LUBRICATION INTERVALS Item Routine Pre operation check Initial Every 1 month or 20 Hrs 3 months or 50 Hrs 6 months or 100 Hrs 12 months or 300 Hrs Spark plug Check condition Clean and replace if necessary Fuel Check fuel level and leakage Fuel hose Chec...

Page 19: ...Recoil starter Check recoil starter for damage Fittings fasteners Check all fittings and fasteners Correct if necessary The point where abnormality was recog nized by use 1 The air filter element needs to be replaced more frequently when using in unusually wet or dusty areas Since these items require special tools data and technical skills have a Yamaha dealer per form the service ...

Page 20: ...se com pressed air to clean the cylinder head cover to prevent dirt from falling into the engine 2 Check 9 Spark plug type Not correct Replace Spark plug type Refer to SPECIFICATIONS in the Supplementary service manual 9 Electrode 1 Wear damage Replace 9 Insulator color 2 Not normal Replace a 1 2 3 Measure 9 Spark plug gap a Use a wire gauge or thickness gauge Out of specification Regap If necessa...

Page 21: ...o prevent threads from being damaged tem porally tighten a the spark plug before tight ening it to the specified torque b a b Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 Spark plug gap Refer to SPECIFICATIONS in the Supplementary service manual TIP Before installing the spark plug clean the gas ket surface and plug surface ...

Page 22: ... warning light 1 Check whether the oil warning light comes on by operating the recoil start er Oil warning light comes on Add oil Oil warning light does not comes on OK 2 Remove 9 Oil filler cap 1 TIP This engine is equipped with two oil filler caps Use whichever side is accessible 3 Check 9 Check that engine oil is at the specified level a Oil level checking steps a Place the engine on a level su...

Page 23: ...drain the engine oil 4 Install 9 Oil drain bolt gasket 3 9 Oil drain bolt 2 Oil drain bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual 5 Fill 9 Engine oil Make sure to fill with the recommended engine oil from the oil filler hole in the crankcase Recommended engine oil Refer to SPECIFICATIONS in the Supplementary service manual Recommended engine oil grade Refer to SPECIFICATION...

Page 24: ...mi cyclone type 3 Check 9 Air filter element Damage Replace Clogged Wash the element with sol vent and then dry it thoroughly Oil the element and squeeze out the excess oil WARNING Do not wash the element with gasoline or with acidic alkalic or organic solvents NOTICE Do not wring out the element This could cause it to tear 4 Install 9 Air filter element 9 Air filter cover 9 Air filter cover screw...

Page 25: ...ve 9 Spark arrester screw 1 2 Remove 9 Spark arrester 1 TIP Use a flathead screw driver to pry the spark arrester out from the muffler 3 Remove 9 Muffler Refer to MUFFLER on 3 7 4 Decarbonize 9 Muffler Tap on the muffler in the area shown in the illustration to loosen carbon build up and then shake it out from the end of the muffler NOTICE Do not use a wire to clean otherwise the noise damping mat...

Page 26: ...efer to TIGHTENINGTORQUES in the Supplementary service manual TIP Align the spark arrester lump a with the hole b in the muffler pipe FUEL TANK FILTER WARNING Do not smoke and keep away from open flames sparks or any other source of fire when handling or in the vicinity of fuel 1 Remove 9 Fuel tank cap 1 9 Fuel tank filter 2 2 Check 9 Fuel tank filter Damage Replace Dirt clog Clean TIP Clean the f...

Page 27: ...nity of fuel 1 Turn the fuel cock lever to the OFF posi tion 2 Remove 9 Strainer cup 1 9 Gasket 2 9 Fuel cock strainer 3 3 Check 9 Fuel cock strainer Damage Replace Dirt clog Clean TIP Clean the fuel cock strainer with clean gaso line and then dry it thoroughly 3 2 1 3 Install 9 Fuel tank filter 9 Fuel tank cap WARNING Make sure that the tank cap is tightened securely ...

Page 28: ...LINDER HEAD on 3 23 3 Install 9 Cylinder head R e fe r t o I N S TA L L I N G T H E CYLINDER HEAD ASSEMBLY on 3 24 BREATHER HOSE 1 Check 9 Breather hose 1 Crack damage Replace Poor connection Correct 1 4 Install 9 Fuel cock strainer 9 Gasket 9 Strainer cup Strainer cup Refer to TIGHTENINGTORQUES in the Supplementary service manual WARNING Make sure that the strainer cup is tight ened securely ...

Page 29: ...er head cover gasket 1 2 3 4 PERIODIC MAINTENANCE 4 Measure 9 Valve clearance Between the rocker arm and valve stem end Out of specification Adjust TIP Valve clearance must be measured when the engine has cooled down enough to be touched Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 3 Pull the recoil starter slowly and then set the piston at TDC top dead center on the compression stroke ...

Page 30: ...er valve clearance Move the thick ness gauge up and down to check for the proper resistance Six piece tappet set YM A5970 Tappet adjusting tool 90890 01311 Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 Adjuster Valve clearance Turn clockwise Decrease Turn counterclockwise Increase c Tighten the locknut 1 Valve adjuster locknut Refer to TIGHTENINGTORQUES in the Supplementary service manua...

Page 31: ...plementary service manual 9 Spark plug cap 1 ENGINE SPEED WITH THROTTLE LEVER MODEL 1 Warm up the engine for a few minutes 2 Attach 9 Digital tachometer 1 Digital tachometer YU 39951 B 90890 06760 3 Measure 9 High engine speed with no load Out of specification Adjust High engine speed Refer to SPECIFICATIONS in the Supplementary service manual a 1 Measurement steps a Move the throttle lever 1 to t...

Page 32: ... service manual ADJUSTING THE ENGINE SPEED WITH THROTTLE LEVER MODEL 1 Warm up the engine for a few minutes 2 Attach 9 Digital tachometer 1 Digital tachometer YU 39951 B 90890 06760 1 PERIODIC MAINTENANCE a 1 4 Measure 9 Low engine speed with no load Out of specification Adjust Low engine speed Refer to SPECIFICATIONS in the Supplementary service manual Measurement steps a Move the throttle lever ...

Page 33: ...ection a High engine speed is decreased Direction b High engine speed is increased c Tighten the throttle stop screw 1 until it touches the throttle lever d Move the throttle lever 2 to direction a until it stops e Turn the throttle stop screw 3 carbu retor in direction c or d until the low engine speed is obtained Low engine speed Refer to SPECIFICATIONS in the Supplementary service manual Direct...

Page 34: ...PEED 1 Warm up the engine for a few minutes 2 Attach 9 Digital tachometer 1 Digital tachometer YU 39951 B 90890 06760 1 a b 1 a b 1 3 Adjust 9 Engine speed Adjustment steps a Turn the throttle stop screw 1 in direc tion a or b until the engine speed is obtained TIP There are two different types of the throttle stop screws Adjust the engine speed accord ing to appropriate illustration Engine speed ...

Page 35: ...nce 1 Warm up the engine for a few minutes 2 Remove 9 Spark plug cap 9 Spark plug NOTICE Before removing the spark plug use com pressed air to clean the cylinder head cover to prevent dirt from falling into the engine 1 2 ENGINE 3 Connect 9 Compression gauge 1 9 Extension 2 Engine compression tester YU 33223 Compression gauge 90890 03081 Extension 90890 04082 3 ...

Page 36: ...imum speci fication a Squirt a few drops of oil into the cylin der b Measure the compression again Reading Diagnosis Higher than without oil 9 Worn cylinder piston and piston ring s Same as without oil 9 Defective piston piston ring s valve s and cyl inder head gasket 9 Improper valve timing and valve clearance Testing steps above the maximum speci fication a Check the cylinder head valve surfac e...

Page 37: ...m kgf 7 2 ft lbf 5 AIR FILTER SILENT SEMI DRY TYPE Order Job Parts to remove Q ty Remarks Removing the air filter Remove the parts in the order listed 1 Air filter cover 1 2 Air filter element 1 3 Element fitting plate 1 4 Plate 1 5 Breather hose 1 6 Air filter case 1 7 Gasket 1 For installation reverse the removal pro cedure ...

Page 38: ...EMI CYCLONE TYPE Order Job Parts to remove Q ty Remarks Removing the air filter Remove the parts in the order listed 1 Air filter cover 1 2 Air filter element 1 3 Breather hose 1 4 Air filter case 1 5 Gasket 1 For installation reverse the removal pro cedure ...

Page 39: ... Nm 0 6 m kgf 4 3 ft lbf 1 2 3 4 5 7 6 Order Job Parts to remove Q ty Remarks Removing the fuel tank and canister Remove the parts in the order listed 1 Fuel hose 1 Turn the fuel cock lever to the OFF position 2 Fuel tank 1 3 Fuel tank stay 1 1 4 Fuel tank stay 2 1 5 Fuel tank stay 3 1 6 Fuel tank cap canister 1 7 Fuel cock 1 For installation reverse the removal pro cedure FUEL TANK CANISTER ...

Page 40: ...3 6 ENG FUEL TANK CANISTER CHECKING THE CANISTER 1 Check 9 Canister 1 Cracks damage Replace 1 ...

Page 41: ...0 m kgf 14 ft lbf 20 Nm 2 0 m kgf 14 ft lbf 3 1 2 4 Order Job Parts to remove Q ty Remarks Removing the muffler Remove the parts in the order listed Fuel tank Refer to FUEL TANK CANISTER on 3 5 1 Muffler 1 2 Gasket 1 3 Muffler cover 1 4 Spark arrester 1 For installation reverse the removal pro cedure MUFFLER ...

Page 42: ...d bolt 3 until just comes in contact with the surface 2 Tighten 9 Muffler nut 1 9 Muffler nut 2 Muffler nut Refer to TIGHTENINGTORQUES in the Supplementary service manual 9 Muffler bolt 3 Muffler bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual TIP Tighten the nuts and bolt to the specified torque in order of muffler nut 1 muffler nut 2 and muffler bolt 3 ...

Page 43: ...der Job Parts to remove Q ty Remarks Removing the recoil starter Remove the parts in the order listed 1 Recoil starter assembly 1 2 Starter handle 1 3 Drive plate 1 4 Clip 1 5 Drive pawl 2 6 Spring 2 7 Sheave drum 1 8 Starter spring 1 9 Starter case 1 10 Starter rope 1 For installation reverse the removal pro cedure RECOIL STARTER ...

Page 44: ...e 9 Drive plate screw 1 9 Drive plate Clip 9 Drive pawls 9 Springs TIP Release the spring preload before removing the drive plate screw 1 Hook the rope into the sheave drum slot a and turn the sheave drum assembly clockwise 3 Remove 9 Sheave drum assembly 1 9 Starter spring 2 9 Starter rope NOTICE Be sure to press down on the sheave drum assembly because the spring will spread out suddenly when it...

Page 45: ...rum from the larger to the smaller diameter 2 Install 9 Sheave drum assembly TIP Engage the spring hook a with the starter case hook b 3 Install 9 Springs 1 9 Drive pawls 2 CHECKING THE RECOIL STARTER 1 Check 9 Starter rope Wear damage Replace 9 Starter case Cracks damage Replace 9 Starter spring Dirt Clean and apply grease Wear damage Replace 2 Check 9 Drive pawls 1 9 Drive plate 2 Wear damage Re...

Page 46: ... drum slot a and turn the sheave drum assembly counterclockwise four times and then unhook the starter rope from the slot 6 Check 9 Recoil starter operation TIP Pull the starter handle several times to check that the sheave drum turns smoothly and to check the starter rope for slack Repeat steps 1 5 if necessary 1 4 Install 9 Drive plate Clip 1 ...

Page 47: ... flywheel Remove the parts in the order listed Air filter Refer to AIR FILTER on 3 3 Fuel tank Refer to FUEL TANK CANISTER on 3 5 Carburetor Refer to CARBURETOR on 4 1 Recoil starter Refer to RECOIL STARTER on 3 9 1 Flywheel cover 1 2 TCI unit 1 3 Starter pulley 1 4 Flywheel 1 5 Woodruff key 1 6 Clamp 1 7 Charging coil 1 With charging coil model For installation reverse the removal pro cedure FLYW...

Page 48: ...y wheel Primary clutch holder YS 01880 A Sheave holder 90890 01701 3 Remove 9 Flywheel 1 9 Woodruff key TIP 9 Remove the flywheel 1 using the flywheel puller 2 9 Fully tighten the tool holding bolts making sure the tool body is parallel with the fly wheel If necessary one bolt may be backed out slightly to level the tool body Heavy duty puller YU 33270 B Flywheel puller 90890 01362 ...

Page 49: ...ary service manual TIP Tighten the flywheel nut 1 using the sheave holder 2 to hold the flywheel Primary clutch holder YS 01880 A Sheave holder 90890 01701 3 Install 9 TCI unit TCI unit bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual Refer to INSTALLING THE TCI UNIT on 3 16 9 Flywheel cover Flywheel cover bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual ...

Page 50: ... Adjust Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 TCI unit air gap Refer to SPECIFICATIONS in the Supplementary service manual 3 Adjust 9 TCI unit air gap Adjustment steps a Loosen the TCI unit bolts 1 b Adjust the TCI unit air gap Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 c Tighten the TCI unit bolts 1 TCI unit bolt Refer to TIGHTENINGTORQUES in the Supplementary servi...

Page 51: ... TANK CANISTER on 3 5 Fuel tank stay Refer to FUEL TANK CANISTER on 3 5 Engine switch and oil warning unit Refer to ENGINE SWITCH AND OIL WARNING UNIT on 3 20 Crankcase cover Refer to PISTON CAMSHAFT CRANKCASE AND CRANKSHAFT on 3 32 1 Clip 1 2 Governor shaft 1 3 Flyweight shaft assembly 1 For installation reverse the removal pro cedure GOVERNOR ...

Page 52: ...t 2 9 Washers 3 3 Remove 9 Flyweight shaft assembly 1 9 Washer 2 TIP Remove the flyweight shaft assembly by tap ping the flyweight shaft from outside of the crankcase cover DISASSEMBLING THE FLYWEIGHT SHAFT ASSEMBLY 1 Remove 9 Weight shafts 1 9 Weights 2 9 Collar 3 9 Washer 4 9 Circlip 5 9 Flyweight shaft 6 CHECKING THE FLYWEIGHT SHAFT ASSEMBLY AND GOVERNOR SHAFT 1 Check 9 Flyweight shaft assembly...

Page 53: ...EMBLY 1 Install 9 Flyweight shaft 1 9 Circlip 2 9 Washer 3 9 Collar 4 9 Weights 5 9 Weight shafts 6 INSTALLING THE FLYWEIGHT SHAFT ASSEMBLY AND GOVERNOR SHAFT 1 Install 9 Washer 1 9 Flyweight shaft assembly 2 2 Install 9 Washers 1 9 Governor shaft 2 9 Clip 3 3 Install 9 Governor arm 9 Crankcase cover R e fe r t o I N S TA L L I N G T H E CRANKCASE COVER on 3 37 3 2 1 1 ...

Page 54: ...ove Q ty Remarks Removing the engine switch and oil warning unit Remove the parts in the order listed Fuel tank Refer to FUEL TANK CANISTER on 3 5 Fuel tank stay Refer to FUEL TANK CANISTER on 3 5 1 Clamp 1 2 Oil warning unit 1 3 Oil warning light 1 4 Engine switch 1 5 Protector 1 For installation reverse the removal pro cedure ENGINE SWITCH AND OIL WARNING UNIT ...

Page 55: ...emarks Removing the cylinder head cover and cylinder head Remove the parts in the order listed below Fuel tank Refer to FUEL TANK CANISTER on 3 5 Muffler Refer to MUFFLER on 3 7 Air filter Refer to AIR FILTER on 3 3 Carburetor Refer to CARBURETOR on 4 1 Flywheel cover Refer to FLYWHEEL on 3 13 1 Spark plug cap 1 2 Spark plug 1 3 Breather hose 1 4 Cylinder head cover 1 5 Cylinder head cover gasket ...

Page 56: ...Nm 0 7 m kgf 5 1 ft lbf 11 Nm 1 1m kgf 8 0 ft lbf 11 Nm 1 1m kgf 8 0 ft lbf 20 Nm 2 0 m kgf 14 ft lbf 2 3 Nm 0 23m kgf 1 7 ft lbf Order Job Parts to remove Q ty Remarks 10 Rocker arm shaft 2 11 Rocker arm 2 12 Push rod 2 13 Cylinder head assembly 1 14 Cylinder head gasket 1 15 Dowel pin 2 For installation reverse the removal pro cedure ...

Page 57: ...fications Replace CHECKING THE CYLINDER HEAD 1 Check 9 Cylinder head combustion chamber Check the combustion chamber for car bon deposits Any carbon deposits Eliminate TIP Be sure not to damage the contact surface of the cylinder 2 Check 9 Cylinder head Cracks damage around the hole of spark plug Replace CHECKING THE ROCKER ARM 1 Check 9 Rocker arm Wear damage cracks Replace ...

Page 58: ...IFICATIONS in the Supplementary service manual Out of specifications Resurface or replace CYLINDER HEAD COVER CYLINDER HEAD 1 2 4 3 5 5 INSTALLING THE CYLINDER HEAD ASSEMBLY 1 Install 9 Cylinder head 9 Cylinder head bolts 1 to 5 TIP Tighten the bolts to the specified torque in two steps and in order from 1 to 5 Cylinder head bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual ...

Page 59: ...ve Remove the parts in the order listed Cylinder head Refer to CYLINDER HEAD COVER CYLINDER HEAD on 3 21 1 Valve cotter 2 2 Valve spring retainer 2 3 Valve spring 2 4 Exhaust valve 1 5 Intake valve 1 6 Valve stem seal 1 Intake side only For installation reverse the removal pro cedure VALVE ...

Page 60: ... using the valve spring compressor 5 TIP Do not compress the spring more than neces sary Valve spring compressor 90890 01253 CHECKING THE VALVE AND VALVE SPRING 1 Measure 9 Valve stem length a 9 Valve head diameter b Valve stem length Refer to SPECIFICATIONS in the Supplementary service manual Valve head diameter Refer to SPECIFICATIONS in the Supplementary service manual Out of specifications Rep...

Page 61: ... Valve spring free length a Valve spring free length Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual Out of specifications Replace a 2 Measure 9 Valve stem diameter a Valve stem diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual Out of sp...

Page 62: ... the valve guide and use a valve lapper to contact the valve face with the valve seat 302 028 a 6 Measure 9 Valve spring tilt a Tilt limit Refer to SPECIFICATIONS in the Supplementary service manual Out of specifications Replace a b 5 Measure 9 Compressed valve spring force a Out of specification Replace the valve spring Installed compression spring force Refer to SPECIFICATIONS in the Supplementa...

Page 63: ...entary service manual Out of specification rough eccentric wear Replace TIP Do not rotate the valve while the valve face is contacting the valve seat 4 Measure 9 Valve face contact width b Make sure that the contact width along the entire valve face is within specifica tions Valve face contact width Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Su...

Page 64: ... to make sure that there are traces of even contact in the center of the valve face 1 6 Remove carbon deposits on the valve face a and valve seat 9 Valve face contact seat width b 9 Valve margin thickness c Apply a small amount of coarse mechanic s blueing dye Dykem to the valve seat Press the valve through the valve guide and onto the valve seat to make a clear impression 9 Valve margin thickness...

Page 65: ... and use the valve spring compressor 5 to install the parts Valve spring compressor 90890 01253 NOTICE Do not compress the valve spring more than necessary TIP Make sure that the blunt edged corner of valve cotter is positioned to the valve spring retainer VALVE NOTICE Do not let the lapping compound enter the gap between the valve stem and the valve guide TIP After every lapping procedure clean o...

Page 66: ... 7 2 ft lbf Order Job Parts to remove Q ty Remarks Removing the piston camshaft crankcase and crankshaft Remove the parts in the order listed Cylinder head assembly Refer to CYLINDER HEAD COVER CYLINDER HEAD on 3 21 Flywheel Refer to FLYWHEEL on 3 13 1 Crankcase cover 1 2 Gasket 1 3 Dowel pin 2 4 Clamp 1 5 Oil level switch 1 6 Flyweight shaft assembly 1 7 Clip 1 8 Governor shaft 1 PISTON CAMSHAFT ...

Page 67: ... 15 10 11 9 Order Job Parts to remove Q ty Remarks 9 Camshaft 1 10 Valve lifter 2 11 Crankshaft shim P T O shaft type E 12 Connecting rod cap 1 13 Crankshaft 1 14 Connecting rod 1 15 Piston pin circlip 2 16 Piston pin 1 17 Piston 1 18 Piston ring set 1 For installation reverse the removal pro cedure ...

Page 68: ...move the camshaft when the camshaft gear mark a and the crankshaft gear mark b are aligned 2 Remove 9 Intake valve lifter 1 9 Exhaust valve lifter 2 NOTICE Mark the intake and exhaust valve lifters so as not to confuse them during reassem bly a b 1 1 2 CHECKING THE CAMSHAFT 1 Check 9 Camshaft Crack damage wear Replace ...

Page 69: ...e Supplementary service manual Out of specification Replace a b 2 Check 9 Camshaft lobe dimensions a and b Camshaft lobe dimensions Dimension a Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual Dimension b Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service...

Page 70: ...NG THE VALVE LIFTER AND CAMSHAFT 1 Install 9 Intake valve lifter 1 9 Exhaust valve lifter 2 2 Install 9 Camshaft 1 NOTICE Be sure to align the camshaft gear mark a with the crankshaft gear mark b a b 1 1 2 CHECKING THE CRANKCASE COVER 1 Check 9 Crankcase cover Damage Replace 9 Bearing Noise wear rotational failure Replace ...

Page 71: ...nder inside diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual Cylinder taper limit Refer to SPECIFICATIONS in the Supplementary service manual a b PISTON CAMSHAFT CRANKCASE AND CRANKSHAFT 8 1 2 3 4 5 6 7 8 INSTALLING THE CRANKCASE COVER 1 Install 9 Crankcase cover 9 Crankcase cover bolts 1 to 8 TIP Tighten the bol...

Page 72: ...r head at six points using a straight edge and thickness gauge CHECKING THE CRANKCASE 1 Check 9 Crankcase Damage Replace 9 Bearing Noise wear rotational failure Replace Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 Warpage limit Refer to SPECIFICATIONS in the Supplementary service manual Out of specification Replace the crankcase ...

Page 73: ...n the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual PISTON CAMSHAFT CRANKCASE AND CRANKSHAFT CHECKING THE PISTON AND PISTON PIN 1 Measure 9 Piston skirt diameter P a 10 mm 0 4 in from the piston bottom edge Out of specification Replace Piston skirt diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in ...

Page 74: ...ide diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual a 4 Measure 9 Piston pin diameter a Out of specification Replace Piston pin diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual ...

Page 75: ... the piston crown so that the ring is at an angle to the cylinder bore Piston ring end gap Limit Top ring Refer to SPECIFI CATIONS in the Supple mentary serv ice manual Refer to SPECIFI CATIONS in the Supple mentary serv ice manual 2nd ring Oil ring 5 Check 9 Check that the piston pin enters smoothly into the piston pin hole TIP If the piston pin fits too tight into the piston check the piston pin...

Page 76: ...grooves and rings before measuring the side clearance 9 Measure the side clearance at several posi tions Feeler gauge set YU 26900 9 Thickness gauge 90890 03180 Piston ring side clearance Limit Top ring Refer to SPECIFI CATIONS in the Supple mentary serv ice manual Refer to SPECIFI CATIONS in the Supple mentary serv ice manual 2nd ring CHECKING THE CRANKSHAFT 1 Check 9 Crankshaft sprocket 1 Damage...

Page 77: ...tside diameter Refer to SPECIFICATIONS in the Supplementary service manual Limit Refer to SPECIFICATIONS in the Supplementary service manual a 2 Measure 9 Crankshaft runout limit Out of specification Replace Use a dial gauge Dial indicator gauge YU A8428 Dial gauge 90890 03097 Runout limit Refer to SPECIFICATIONS in the Supplementary service manual ...

Page 78: ...e of Plastigauge 1 on the crank pin horizontally TIP Wipe off oil thoroughly from the crankshaft connecting rod and connecting rod cap 2 Install 9 Connecting rod 1 9 Connecting rod cap 2 Connecting rod cap bolt Refer to TIGHTENINGTORQUES in the Supplementary service manual TIP Tighten the cap bolts so that the crankshaft does not move while the oil clearance is being measured 1 1 2 ...

Page 79: ... the engine oil to the inside of the connecting rod small end 1 2 3 1 2 3 a 3 Remove 9 Connecting rod cap 9 Connecting rod 4 Measure 9 Connecting rod big end oil clearance Out of specification Replace crank shaft or connecting rod assembly and then measure the clearance again TIP Measure the widest portion of the pressed Plastigauge Connecting rod big end oil clear ance Refer to SPECIFICATIONS in ...

Page 80: ...he pis ton head faces toward the push rod 9 Install the piston pin clips so that the clip ends are 45 c or more from the cutout in the piston b a 1 3 2 45 90 90 90 a b c d c 1 2 3 INSTALLING THE CRANKSHAFT 1 Make sure that the end gap of each pis ton ring is positioned correctly as shown in the illustration a Lower oil ring rail b 2nd ring c Upper oil ring rail d Top ring oil ring expander 2 Insta...

Page 81: ...Attach the piston ring compressor to the pis ton and then insert the piston into the cylin der 4 Check 9 Piston with the connecting rod 1 posi tion TIP 9 Make sure that the mark a on the pis ton head faces toward the push rod 9 Make sure that the YAMAHA mark b on the connecting rod faces toward the crank case cover 1 5 Install 9 Crankshaft 1 ...

Page 82: ... alter nately two to three times 7 Install 9 Camshaft Refer to INSTALLING THE VALVE LIFTER AND CAMSHAFT on 3 36 9 Crankcase cover R e fe r t o I N S TA L L I N G T H E CRANKCASE COVER on 3 37 a SELECTING THE CRANKSHAFT SHIM P T O SHAFT TYPE E 1 Measure 9 Crankshaft free play a Out of specification Adjust Crankshaft free play Refer to SPECIFICATIONS in the Supplementary service manual 2 Calculate 9...

Page 83: ... the proper thickness c Install the crankcase cover 1 R e fe r t o I N S TA L L I N G T H E CRANKCASE COVER on 3 37 d Measure the crankshaft free play again TIP Repeat these steps until the free play is within specification Shim thickness table Part number Shim thickness 7VB E1561 00 0 1 0 03 mm 0 0039 0 0012 7VB E1561 10 0 2 0 05 mm 0 0079 0 0020 7VB E1561 20 0 3 0 05 mm 0 0118 0 0020 7VB E1561 3...

Page 84: ...arts in the order listed Fuel tank Refer to FUEL TANK CANISTER on 3 5 Air filter Refer to AIR FILTER on 3 3 1 Choke solenoid lead 2 Auto choke model 2 Link rod Spring 1 1 3 Carburetor assembly 1 4 Gasket 1 5 Joint 1 6 Gasket 1 For installation reverse the removal pro cedure CARBURETOR REMOVING THE CARBURETOR A Auto choke model ...

Page 85: ...1 5 Gasket 1 6 Main jet 1 7 Float pin 1 8 Float 1 9 Needle assembly 1 0 Pilot screw Spring 1 1 2 turns out q Pilot jet O ring 1 1 w Throttle stop screw Spring 1 1 For assembly reverse the disassembly procedure 1 2 3 4 5 6 7 8 9 0 q w 2 0 Nm 0 20 m kgf 1 4 ft lbf 3 5 Nm 0 35 m kgf 2 5 ft lbf 1 3 Nm 0 13 m kgf 0 94 ft lbf 9 Nm 0 9 m kgf 6 5 ft lbf 0 7 Nm 0 07 m kgf 0 52 ft lbf 0 7 Nm 0 07 m kgf 0 52...

Page 86: ...bf 3 5 Nm 0 35 m kgf 2 5 ft lbf 1 0 Nm 0 10 m kgf 0 72 ft lbf 5 Nm 0 5 m kgf 3 6 ft lbf Order Job Parts to remove Q ty Remarks Disassembling the carburetor Disassemble the parts in the order listed 1 Drain screw 1 2 Float chamber bolt 1 3 Gasket 1 4 Float chamber 1 5 Gasket 1 6 Main jet 1 7 Float pin 1 8 Float 1 9 Needle assembly 1 0 Pilot screw Spring 1 1 2 turns out q Pilot jet O ring 1 1 w Thro...

Page 87: ...y 1 For assembly reverse the disassembly procedure r 1 3 Nm 0 13 m kgf 0 94 ft lbf 7 Nm 0 7 m kgf 5 1 ft lbf 0 7 Nm 0 07 m kgf 0 52 ft lbf 0 7 Nm 0 07 m kgf 0 52 ft lbf 3 5 Nm 0 35 m kgf 2 5 ft lbf 2 0 Nm 0 20 m kgf 1 4 ft lbf 3 5 Nm 0 35 m kgf 2 5 ft lbf 1 0 Nm 0 10 m kgf 0 72 ft lbf 5 Nm 0 5 m kgf 3 6 ft lbf ...

Page 88: ... the float arm and then measure the float height a 9 Do not adjust the float height Float height Refer to SPECIFICATIONS in the Supplementary service manual 2 Check 9 Jets 9 Carburetor body Check for clogging Clogged Apply compressed air to clean the jet 3 Check 9 Valve seat Wear damage Replace Dirt Clean a Wear at groove b Dirt a a b DISASSEMBLING THE CARBURETOR ...

Page 89: ...id Connect the pocket tester Ω 1 Measure the choke solenoid resist ance Choke solenoid resistance Refer to SPECIFICATIONS in the Supplementary service manual Analog pocket tester YU 03112 C Pocket tester 90890 03112 Out of specification Replace Ω 1 DISASSEMBLING THE CARBURETOR ...

Page 90: ...C ELECTRICAL COMPONENTS ELECTRICAL ELECTRICAL COMPONENTS 1 2 3 4 5 6 7 1 Spark plug 2 TCI unit 3 Charging coil With charging coil model 4 Oil warning unit 5 Engine switch 6 Oil level switch 7 Oil warning light ...

Page 91: ...t the engine switch to STOP when checking or replacing a fuse 1 1 Remove 9 Fuse 1 2 Check 9 Fuse Checking steps a Connect the pocket tester Ω 1 to the fuse and check the continuity TIP Set the pocket tester selector to Ω 1 Analog pocket tester YU 03112 C Pocket tester 90890 03112 b If the pocket tester indicates replace the fuse ...

Page 92: ... electrical circuit is operational d If the fuse immediately blows again check the electrical circuit Fuse amperage Refer to SPECIFICATIONS in the Supplementary service manual WARNING Never use a fuse with an amperage other than that specified Improvising or using a fuse with the wrong amperage rating may cause extensive damage to the electrical system and could possibly cause a fire 4 Install 9 F...

Page 93: ...ket tester 90890 03112 TIP 9 Set the pocket tester to 0 before starting a test 9 To test the switch for continuity set the pocket tester to the Ω 1 range 9 Turn the switch on and off several times during the test A A typical example of switch continuity test Measurement example of the electric compo nents A Connect the connector and check W W W W A A B B Disconnect the connector and check SWITCHES...

Page 94: ...ester YU 03112 C Pocket tester 90890 03112 Oppama pet 4000 spark checker YM 34487 Ignition checker 90890 06754 1 Engine oil level 9 Check the oil level Refer to ENGINE OIL LEVEL on 2 5 2 Spark plug 9 Check the spark plug condition Refer to SPARK PLUG on 2 3 Add engine oil MEETS SPECIFICATION OUT OF SPECIFICATION Repair or replace the spark plug GOOD NOT GOOD ...

Page 95: ...tion checker 2 as shown a 1 2 3 Spark plug cap 1 Ignition checker 2 Ignition checker lead Spark plug 3 9 Turn the crankshaft and measure the ignition spark gap a Minimum spark gap Refer to SPECIFICATIONS in the Supplementary service manual MEETS SPECIFICATION OUT OF SPECIFICATION OR NO SPARK The ignition system is good ...

Page 96: ...ice manual 5 Air gap 9 Measure the thickness between the magnet rotor and TCI unit TCI unit air gap Refer to SPECIFICATIONS in the Supplementary service manual TIP 9 Do not pull out the spark plug cap from the high tension cord 9 Remove Turn the spark plug cap coun terclockwise 9 Install Turn the spark plug cap clockwise 9 Check the high tension cord for cracks or deterioration before installing t...

Page 97: ... Supplementary service manual 7 Ignition coil TCI unit resistance 9 Remove the ignition coil TCI unit 9 Connect the pocket tester Ω 1k to the secondary terminal 1 2 Tester lead High tension cord 1 Tester lead Black White terminal 2 Secondary coil resistance Refer to SPECIFICATIONS in the Supplementary service manual Replace the TCI unit MEETS SPECIFICATION OUT OF SPECIFICATION IGNITION SYSTEM Repl...

Page 98: ... 9 Connect the pocket tester Ω 1 to the engine switch connectors 9 Check the engine switch continuity a b 1 2 Tester lead Black terminal 1 Tester lead Black terminal 2 Switch ON a No continuity Switch OFF b Continuity Replace the engine switch MEETS SPECIFICATION OUT OF SPECIFICATION ...

Page 99: ...nd check for conti nuity 1 2 1 2 A B Tester lead Oil level switch lead 1 Tester lead Body ground 2 A Continuity Correct B No continuity Correct 10 Wire harness 9 Check the terminal of the connector for contamination rust or disconnection Replace the oil level switch MEETS SPECIFICATION OUT OF SPECIFICATION Correct or replace the connector Replace the TCI unit GOOD NOT GOOD IGNITION SYSTEM Replace ...

Page 100: ...attery voltage 9 Connect the pocket tester DC 20 V to the battery terminals 9 Measure the battery voltage Tester lead battery positive terminal Tester lead battery negative terminal Battery voltage 12 8 V or more Replace the fuse 9 Clean the battery terminals 9 Recharge or replace the battery CONTINUITY NO CONTINUITY OUT OF SPECIFICATION TIP Use the following special tool s for troubleshooting Ana...

Page 101: ...upler 9 Check the starter motor operation Replace the engine switch MOVES MOVES 1 Jumper lead 1 Jumper lead Replace the starter relay DOES NOT MOVE Check the battery DOES NOT MOVE GOOD NOT GOOD Repair and or charge the battery Repair and or replace the starter motor WARNING 9 A wire that is used as a jumper lead must have the equivalent capacity or more as that of the battery lead other wise the j...

Page 102: ... 1 16 Nm 1 6 m kgf 12 ft lbf 16 Nm 1 6 m kgf 12 ft lbf Order Job Parts to remove Q ty Remarks Removing the starter motor Remove the parts in the order listed 1 Starter motor assembly 1 For installation reverse the removal pro cedure REMOVING THE STARTER MOTOR ...

Page 103: ...8 Nm 0 8 m kgf 5 8 ft lbf Order Job Parts to remove Q ty Remarks Disassembling the starter motor Disassemble the parts in the order listed 1 Rear bracket 1 2 Plate 1 3 Brush holder 1 4 Brush spring 4 5 Brush 4 6 Yoke 1 7 Armature 1 8 Magnetic switch 1 9 Starter drive lever 1 0 Starter case 1 For assembly reverse the disassembly procedure ...

Page 104: ...e commutator Depth of insulator a Refer to SPECIFICATIONS in the Supplementary service manual TIP The mica insulation of the commutator must be undercut to ensure proper operation of the commutator 3 Measure 9 Armature coil insulation continuity Defects Replace the starter motor Connect the pocket tester to the arma ture coil Analog pocket tester YU 03112 C Pocket tester 90890 03112 Commutator con...

Page 105: ...manual 2 Check 9 Brush spring 2 Fatigue damage Replace Assembly 1 Reverse the disassembly steps Refer to DISASSEMBLING THE STARTER MOTOR on 5 14 1 CHECKING THE MAGNETIC SWITCH 1 Measure 9 Magnetic switch 1 coil resistance Connect the pocket tester Ω 1 to the magnetic switch Analog pocket tester YU 03112 C Pocket tester 90890 03112 Out of specification Replace 1 Continuity check 2 Insulation check ...

Page 106: ...ng coil resistance å Refer to SPECIFICATIONS in the Supplementary service manual Pull in coil resistance å ç Refer to SPECIFICATIONS in the Supplementary service manual ELECTRIC STARTING SYSTEM ELECTRIC STARTING MODEL ...

Page 107: ...log pocket tester YU 03112 C Pocket tester 90890 03112 1 Charging coil resistance 9 Disconnect the charging coil leads 9 Connect the pocket tester Ω 1 1 2 Measure the charging coil resistance Charging coil resistance Connector 1 Ground 2 Refer to SPECIFICATIONS in the Supplementary service manual Replace the charging coil OUT OF SPECIFICATION Check and repair wiring to the charging coil MEETS SPEC...

Page 108: ...eck if the fuel tank cap is clogged GOOD CLOGGED Set to ON Check the fuel cock lever position ON OFF Clean or replace the fuel tank or fuel hose Check if fuel flows to fuel cock FLOW OK NO FLOW Check that the oil warning light comes on by pull ing the starter rope LIGHTS ON DOSE NOT LIGHT Check the connections between the oil warning unit and oil level switch GOOD NOT GOOD Replace the oil warning ...

Page 109: ... to the spark plug cap and then ground the spark plug to check for spark GOOD SPARK WEAK OR NO SPARK Clean or replace 9 Check the spark plug for dirt and check the spark plug gap 9 Check for the voltage leakage due to faulty con nection or broken insulation of the high tension cord 9 Check the TCI unit connector for corrosion or faulty connection 9 Check the ignition system Refer to IGNITION SYSTE...

Page 110: ...GINE Correct Check if the marks on the crankshaft and cam shaft are aligned ALIGNED NOT ALIGNED Rebore or replace Check if there is seizure wear or damage on the piston piston ring or cylinder GOOD SEIZURE OR WORN ...

Page 111: ...9 Tighten the carburetor nuts securely 9 Replace the carburetor joint or gasket with a new one Check if there is air suction from the carburetor joint gasket or throttle shaft GOOD NOT GOOD Adjust Measure the valve clearance GOOD OUT OF SPECIFICATION Clean Check if the fuel hose is clogged GOOD CLOGGED Adjust Check the TCI unit air gap GOOD NOT GOOD Repair or replace Check if there is seizure wear...

Page 112: ...ECIFICATION Resurface or replace Check the valve face and valve seat for wear GOOD WORN Correct Check if the marks on the crankshaft and cam shaft are aligned GOOD NOT GOOD Rebore or replace Check if there is seizure wear or damage on the piston piston ring or cylinder GOOD SEIZURE OR WORN Clean the parts Check if the main passages such as the main jet in the carburetor are clogged GOOD CLOGGED 9 ...

Page 113: ... plug for dirt and check the spark plug gap GOOD DIRTY OR OUT OF SPECIFICATION 9 Tighten the carburetor nuts securely 9 Replace the carburetor joint or gasket with a new one Check if there is air suction from the carburetor joint gasket or throttle shaft GOOD NOT GOOD Clean the parts Check if the slow or main passages such as pilot jet and main jet in the carburetor are clogged GOOD NOT GOOD Adjus...

Page 114: ...eck if there is seizure wear or damage on the piston piston ring or cylinder GOOD SEIZURE OR WORN Resurface or replace Check the valve face and valve seat for wear GOOD WORN Adjust Check the valve clearance SUFFICIENT OUT OF SPECIFICATION ...

Page 115: ... that the governor link operate smoothly GOOD NO GOOD Replace Check that the governor spring is stretched GOOD STRETCHED Adjust Check the governor adjustment GOOD NOT GOOD Adjust or replace Check the governor weight and governor bushing function GOOD NOT GOOD ...

Page 116: ...6 9 TRBL ...

Page 117: ...cover indd 3 2012 10 30 12 01 25 ...

Page 118: ...2012_09 1 cover indd 4 2012 10 30 12 01 25 ...

Search results

Summary of Contents for MZ250

Reviews:

Related manuals for MZ250

Brands by name

Popular brands

Yamaha MZ250, Service Manual

Search results

Summary of Contents for MZ250

Reviews:

Related manuals for MZ250

Brands by name

Popular brands