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CENTURY 125 i.e E4
E n g i n e W o r k s h o p M a n u a l

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Do you have a question about the Century 125 and is the answer not in the manual?

Questions and answers

Alan Greenhalgh
March 21, 2025

Hi How do I change the battery on my Rieju 125 Century.

1 comments:
Mr. Anderson
May 14, 2025

To change the battery on a RIEJU Century 125, follow these general steps:

1. Turn off the ignition and ensure the motorcycle is stable on a stand.

2. Locate the battery compartment, which is typically under the seat or side panel.

3. Remove the seat or panel using appropriate tools (like a screwdriver or wrench).

4. Disconnect the battery terminals, starting with the negative (-) terminal, then the positive (+) terminal.

5. Remove the old battery from its holder.

6. Insert the new battery (e.g., BS Battery BT7B-4 for model years 2021–2023).

7. Reconnect the terminals, positive (+) first, then negative (-).

8. Secure the battery and reinstall the seat or panel.

9. Turn on the ignition to check if the battery works properly.

Always follow safety precautions and consult the service manual if needed.

This answer is automatically generated

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Summary of Contents for RIEJU Century 125

  • Page 1 CENTURY 125 i.e E4 E n g i n e W o r k s h o p M a n u a l...
  • Page 2 Not all versions/models shown in this publication are available in all countries. The availability of each model should be checked at the official RIEJU sales network. © Copyright 2014 - Rieju S.A. All rights reserved. Reproduction of this publication in whole or in part is prohibited.
  • Page 3 ENGINE WORKSHOP MANUAL Century 125 i.e. This manual for service stations was made by Rieju S.A. to be used by the workshops of dealers and sub-agencies RIEJU. It is assumed that users of this publication for the maintenance and repair of Rieju vehicles has a basic knowledge of the principles of mechanics and technique procedures of vehicle repair.
  • Page 4 Index 1. GEARBOX 2. STARTER MOTOR 3. GENERATOR SIDE 4. CLUTCH SIDE a. Checking the clutch b. Cheecking the springs 5. CRANKCASE a. Bushing slection 6. HEAD AND TIMING a. Checking the overhead camshaft b. Valve check c. Valve clerance b.
  • Page 5 Engine...
  • Page 6 Engine Gearbox Gearbox shafts Disassembling the gearbox • Open the crankcase halves. • Remove the gaskets from the crank- case. • Take out both fork rods and the trans- mission forks (1) (2). • Take out the desmodromic control (3). •...
  • Page 7: Assembling The Gearbox

    Engine THE CLASS AS WELL AS BEING REPRODUCED ON TWO COUPLING ELEMENTS IS ALSO SHOWN ON THE TWO CRANKCASE HALVES OF THE CRANKCASE. NOTE CRANKCASE SPARE PARTS ARE ALWAYS CLASS X. Checking the desmodromic drum • Check the contact zone on fork (1) and the driving pin (2) of the forks for wear. •...
  • Page 8 Engine • Position the desmodromic drum in the crankcase (3). • Fit the two axles of the transmission forks (1)(2). • Fit the two transmission forks. • Finally, fit the crankshaft. Starter motor TARTER OTOR pos. Description Type Quantity Torque Notes Starter motor fixing screw M6x25...
  • Page 9: Removing The Starter Motor

    Engine Removing the starter motor • Undo and remove the two fixing screws (1). • Remove the starter motor (2). NOTE THE STARTER MOTOR CAN ALSO BE REMOVED IF THE ENGINE IS FITTED TO THE VEHICLE. Installing the starter motor •...
  • Page 10 Engine pos. Description Type Quantity Torque Notes Timing control cover 3.5 - 4.5 Nm (2.58 - 3.31 lbf ft) Oil dipstick M12x1.5 4 - 6 Nm (2.95 - 4.42 lbf IGNITION UNIT pos. Description Type Quantity Torque Notes Flywheel rotor fixing screw M14x1.5 83 - 90 Nm (61.21 - 66.38 lb ft)
  • Page 11: Magneto Flywheel Removal

    Engine Magneto flywheel removal • Remove the starter motor gear. • Position the locking tool. • Unscrew and remove the hex head screw and retrieve the washer. • Position the tool. • Remove the flywheel and its spline.
  • Page 12 Engine • Remove the oil filter.
  • Page 13: Installing The Flywheel

    Engine Freewheel removal • Undo and remove the screw from the lock. • Remove the freewheel. Installing the flywheel For refitting follow the operations described previously in reverse order. See also Magneto flywheel removal...
  • Page 14 Motor Clutch side LUTCH COVER pos. Description Type Quantity Torque Notes Clutch cover fixing screw M6x35 11 - 13 Nm (8.11 - 9.58 lbf ft) Oil filter cover M56x1.5 24 - 26 Nm (17.70 - 19.17lbf ft) Oil pressure sensor 12 - 14 Nm (8.85 - 10.32 lbf ft)
  • Page 15: Removing The Clutch Cover

    Engine LUTCH pos. Description Type Quantity Torque Notes Clutch spring screw 3.5 - 4.5 Nm (2.58 - 3.31 lbf ft) Clutch housing retainer nut 35 - 45 Nm (25.81 - 33.19 lbf ft) Removing the clutch cover • Unscrew and remove the three water pump cover screws.
  • Page 16 Engine • Unscrew and remove the oil filter plug. • Remove the spring and oil filter.
  • Page 17: Disassembling The Clutch

    Engine • Unscrew and remove the ten clutch cover screws. • Remove the clutch cover and the gas- ket. • Collect the dowel pins. WARNING REPLACE THE GASKET DURING REFITTING. • Remove the lubrication circuit by-pass spring. Disassembling the clutch •...
  • Page 18 Engine • Remove the thrust bearing. • Remove the discs. • Release the screw by lowering the lock tab. • Block clutch bell rotation using the spe- cific tool. • Unscrew and remove the clutch bell fixing nut. • Remove the clutch hub. •...
  • Page 19: Checking The Clutch Plates

    Engine • Remove the shim. Checking the clutch plates Characteristic Driving plates thickness 2.85 - 2.95 mm (0.112 - 0.116 in) Number of driving plates Driven plates thickness 1.46 - 1.53 mm (0.057 - 0.06 in) Number of driven plates Checking the clutch housing COUPLING CLASSES The gears that are coupled to each other: clutch housing, first gear shaft and balancing countershaft,...
  • Page 20 Engine Check the primary driven gear for damage and wear and, if necessary, replace the primary driven gear and the clutch bell all together. Make sure there is not excessive noise during op- eration; if necessary, replace the primary drive gear and the clutch bell all together.
  • Page 21: Assembling The Clutch

    Engine Checking the springs • Check the springs for damage and, if necessary, replace the them all togeth- • Measure the clutch spring length when unloaded; if necessary, replace the springs all together. Characteristic Minimum wear limit in the release position of the individual clutch springs 31.6 mm (1.24 in) Assembling the clutch...
  • Page 22 Engine • Insert the clutch hub. • Screw in the retainer nut locking the rotation of the clutch housing with the specific tool. • Lift one side of the lock tab. • Insert the disc covered with the friction material into the bell. •...
  • Page 23 Engine • Insert a new gasket. • Position the dowel pins and the cover. • Position the clutch cable support. • Screw in the ten screws, tightening di- agonally and in stages. • Refit the water pump. • Refit the oil filter. •...
  • Page 24 Engine RANKSHAFT pos. Description Type Quantity Torque Notes Countershaft gear retainer nut 35 - 45 Nm (25.81 - 33.19 lbf ft) Balancing countershaft removal • Before taking out the balancing coun- tershaft the clutch cover and flywheel cover must be removed. •...
  • Page 25 Engine Removing the clutch cover Removing the flywheel cover • Remove the countershaft gear. • Remove the countershaft from the al- ternator side. Balancing countershaft fitting • Insert the countershaft from the alter- nator side. • Insert the gear aligning its reference to the primary gear.
  • Page 26 Engine Crankcase opening • Beforehand remove the clutch cover and the clutch. • Remove the gear selector. • Install the countershaft blocking tool. • Remove the primary gear unscrewing and removing the nut. • Collect the washer. • Remove the countershaft gear. •...
  • Page 27 Engine • Remove the chain guide slider, un- screwing and removing the fixing screw. • Remove the timing chain gear. • Remove the pump drive gear, remov- ing the seeger and recovering the washer. • Remove the base gear of the main shaft.
  • Page 28 Engine • Remove the oil pump unscrewing the three fixing screws. • Collect the gasket. • Remove the gear spider screw, un- screwing and removing the fixing screw. • Moving from the left side of the engine, remove the flywheel and all of its com- ponents beforehand.
  • Page 29: Bearing Removal

    Engine • Unscrew and remove the five screws (3). • Unscrew and remove the short screw (4). • Remove the left crankcase. Bearing removal • Heat the crankcase surface with a heat gun. • Remove the bearing using the extractor. Crankcase check There are two classes of couplings highlighted on the crankcases (X-Y and S-T).
  • Page 30 Engine Therefore, the couplings will be: COUPLING CLASSES CLUTCH HOUSING - FIRST GEAR SHAFT Coupling classes on Crankcase Clutch housing gear Transmission gear The coupling between the gears of the first gear shaft and gear of the balancing countershaft has been classified into two classes.
  • Page 31: Crankshaft Check

    Engine The classes of the transmission elements are also listed on the two crankcase halves. NOTE CRANKCASE SPARE PARTS ARE ALWAYS CLASS X. Crankshaft check • Before checking the crankcase halves, thoroughly clean all the surfaces and the oil pipes. •...
  • Page 32 Engine Bushing selection USHING SEAT DIAMETER ON CRANKCASE Specification Desc./Quantity Class 1 MIN 36.500 mm (1.4370 in) MAX 36.508 mm (1.4373 in) Class 2 MIN 36.508 mm (1.4373 in) MAX 36.516 mm (1.4376 in) RANKSHAFT DIAMETER Specification Desc./Quantity Class 1 MIN 32.480 mm (1.2787 in) MAX 32.485 mm (1.2789 in) Class 2...
  • Page 33 Engine • Position and screw the short screw (4). • Position and screw the five screws (3). See also Assembling the gearbox • Position and screw the long screw (2). • Moving from the left side of the crank- case, position and screw the six screws (1).
  • Page 34 Engine • Fit a new oil pump gasket. • Fit the oil pump, screwing the three screws. • Insert the countershaft gear and posi- tion the washer. • Use the specific tool to tighten the nut. • Apply the cotter to the main shaft. •...
  • Page 35 Engine • Insert the pump drive gear. • Insert the washer and apply the fixing seeger. • Insert the timing chain gear, paying at- tention to the direction. The engraving must face upward. • Fit the timing chain. • Position the chain guide slider. •...
  • Page 36 Engine • Fit the gear selector. Head and timing EAD COVER pos. Description Type Quantity Torque Notes Spark plug 12 - 14 Nm (8.85 - 10.32 lbf ft) Head cover fixing screw 10 - 12 Nm (7.38 - 8.85 lbf ft)
  • Page 37: Removing The Head Cover

    Engine ALVES pos. Description Type Quantity Torque Notes Head fastener screw, chain side M6x130 11 Nm (8.11 lbf ft) Exhaust side fixing stud bolt M8x40 12 Nm (8.85 lbf ft) Camshaft support fixing screw M6x40 10 Nm (7.38 lbf ft) Head fixing screw M8x166 25 Nm + 90°...
  • Page 38 Engine • Unscrew and remove the four cylinder head screws (2). • Remove the cylinder head (3). • Remove the gasket (4). • Remove the spark plug.
  • Page 39 Engine Removing the timing control • Turn the crankshaft from the hole on the cover (1) • Take the piston to TDC. • The sign (2) must be aligned with the sign (3). • Insert the specific pins (4) on the valves cam tower.
  • Page 40 Engine • Lock the timing gear using the tool. • Unscrew and remove the gear. • Repeat the operation with the other gear. Cylinder head Removing the overhead camshaft • Unscrew and remove the six screws (1) 1) ) a •...
  • Page 41 Engine • Remove the cylinder head (3). • Remove the two pins from the valves cam tower. • Remove the eight screws (1). • Remove the valve cam tower (2). • Remove the two camshafts, intake and exhaust side.
  • Page 42: Removing The Valves

    Engine Removing the valves • Remove the head. • Place the head on supporting surface. • Number the valves and their bucket tappets in order to position them cor- rectly upon refitting. • Remove the valve bucket tappets. • Compress the valve spring using the tool.
  • Page 43: Valve Check

    Engine • Release the valve springs. • Remove the cap and the valve spring. Checking the overhead camshaft • Check the camshaft bearings for signs of abnormal wear. Characteristic Standard diameter - Bearing A 19.980 - 19.959 mm (0.7866 - 0.7858 in) Minimum diameter allowed - Bearing A 19.95 mm (0.7854 in) Inlet cam height...
  • Page 44 Engine 3.95 mm (0.1555 in) Standard clearance - Intake: 0.015/0.042 mm (0.00059/ 0.0016 in) Standard clearance - Exhaust: 0.025/0.052 mm (0.00098/ 0.00204 in) Maximum clearance admitted - Intake: 0.060 mm (0.0023 in) Maximum clearance admitted - Exhaust: 0.070 mm (0.0027 in) Remove the head cover.
  • Page 45 Engine • Use a feeler gauge to check clearance on the four valves. • If the values measured differ from the values specified, record the difference between MAXIMUM ALLOWED CLEARANCE e CLEARANCE MEAS- URED. • Remove the chain tensioner. • Undo and remove the eight screws and remove the cam tower.
  • Page 46: Inspecting The Valve Sealings

    Engine • Remove the bucket tappet of the valve in question and read the calibration val- ue for that bowl, found inside the buck- et tappet itself. • Replace the bucket tappet with new one of a size suitable to restore the correct clearance.
  • Page 47: Inspecting The Valve Housings

    Engine - Measure the sealing surface width on the valv seats. VALVE SEALING SURFACE Specification Desc./Quantity Inlet valve - seal surface 2.30 +/- 0.15 mm (0.0905 +/- 0.0059 in) Outlet valve - seal surface 2.95 +/- 0.15 mm (0.1161 +/- 0.0059 in) Valve chamfering 0.2 +/- 0.1 mm x 45°...
  • Page 48: Inspecting The Springs And Half-Cones

    Engine Inspecting the springs and half-cones • Check that the spring upper supporting caps and the cotters show no signs of abnormal wear. • Check the unloaded spring length. Characteristic Valve spring length: 33.24 +/- 0.25 mm (1.3086 +/-0.0098 in) Checking the cylinder head •...
  • Page 49: Checking The Chain

    Engine Checking the chain tensioner CHAIN TENSIONER • Remove the central screw with the washer and the tensioner spring. Check that the one-way mechanism is not worn. • Check the condition of the tensioner spring. • If signs of wear are found, replace the whole assembly.
  • Page 50: Removing The Cylinder

    Engine YLINDER ISTON pos. Description Type Quantity Torque Notes Chain tensioner screw 6 Nm (4.43 lbf ft) Removing the cylinder CYLINDER REMOVAL • Remove the cylinder head gasket (1). • Remove the guide slider (2). • Remove the water sleeve clamp (3).
  • Page 51 Engine • Remove the cylinder (4). • Remove the gasket (5). Disassembling the piston • Apply the tool under the piston (1). • Cover the base of the cylinder with a cloth. • Remove the retainer ring which locks the pin (2). •...
  • Page 52: Checking The Piston

    Engine Checking the piston • Measure the pin seat diameter on the piston. • Calculate the pin - piston coupling clearance. • Measure the piston outside diameter, perpendicular to the pin axis. • Take the measurement at 6 mm (0.24 in) from the base, at the position shown in the figure.
  • Page 53: Inspecting The Wrist Pin

    Engine - top ring: +0.03 / 0.062 mm (0.0012 / 0.0024 in - middle ring: +0.02 / 0.052 mm (0.0008 / 0.0020 in - oil scraper: +0.01 / 0.19 mm (0.0004 / 0.007480 in cylinder check • Using a bore meter, measure the cyl- inder inside diameter at three different points according to the directions shown in the figure.
  • Page 54: Fitting The Piston

    Engine Specification Desc./Quantity Oil scraper ring 0.2 / 0.7 mm (0.0079 / 0.027 in) Top ring maximum value 0.45 mm (0.18 in) Middle ring maximum value 0.45 mm (0.18 in) Checking the connecting rod small end • Measure the inside diameter of the connecting rod small end using a spe- cific micrometer.
  • Page 55: Installing The Cylinder

    Engine • Temporarily install the cylinder on the piston, without the gasket of the cylin- der's base. • Fit a dial gauge on the specific tool. • Take the piston to TDC. • Position the dial gauge on one side of the cylinder and fasten it in order to de- tect the zero position correctly.
  • Page 56: Installing The Cylinder Head

    Engine • Fit a new gasket between the cylinder and the head. • Place the two dowels. • Install the head. Selecting the base gasket BASE GASKET SELECTION Specification Desc./Quantity Size measured: 0.95 / 1.09 mm (0.037 - 0.042 in) Gasket 0.3+/-0.05 mm (0.012+/-0.001 in) Size measured: 1.1 / 1.25 mm (0.043 - 0.049 in) Gasket 0.4+/-0.05 mm (0.015+/-0.001 in)
  • Page 57 Engine • Insert the timing control chain on the crankshaft. • Insert the chain tensioner pad of the head and lock it with the fixing screw. • Insert the camshafts in their seats on the head, remember to position the camshaft marked with the letter (A) on the intake side and the camshaft marked with the letter (S) on the ex-...
  • Page 58 Engine • Place the camshaft gears on the chain, be careful not to invert the original di- rection of rotation. • Keep the camshafts locked with the pins and screw but do not tighten the screws fixing the gears using Loctite 243.
  • Page 59: Conceptual Diagrams

    Engine Lubrication pos. Description Type Quantity Torque Notes Oil pump fixing screw M6x25 10 Nm (7.38 lbf ft) Loctite 243 Conceptual diagrams...
  • Page 60 Engine Removing • Remove the Seeger ring. • Remove the pump gear. • Remove the pump gear. • Separate the components to inspect them.
  • Page 61 Engine Inspection • Measure distance between rotors with a feeler gauge at the positions shown in the picture. Characteristic Oil intake rotor Thickness: 13.5 mm (0.53 in) Oil supply rotor Thickness: 8.5 mm (0.33 in) Standard values Radial clearance (1) between points of the rotor: 0.04 mm (0.0015 in) Radial clearance (2) between points of the rotor: 0.08 mm (0.003 in)
  • Page 63 RIEJU, S.A. c/.Borrassà, 41 E-17600 FIGUERES, GIRONA (SPAIN) Telf. +34 / 972500850 Fax +34 / 972506950 www.riejumoto.com / e-mail rieju@riejumoto.com...

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