General Installation Method for 12V Starter Motors of Sisu, Ursus, Valtra/Valmet, and Valmet

I. Pre-installation Preparation (General)

1. Tools and Materials

• Special Tools: 10–19mm socket wrench set, torque wrench, Phillips/flathead screwdriver, wire crimping tool, insulating tape/heat shrink tubing

• Auxiliary Materials: OEM grade 8.8 or higher high-strength mounting bolts, flat washers, spring washers, conductive paste, medium-strength threadlocker (e.g., Loctite 243)

• Safety Protection: Disconnect the negative battery cable (for 12V single-battery systems, disconnect the negative terminal directly). Wear gloves and safety goggles. Clean oil, dirt, and rust from the installation area in the engine compartment or on the tractor engine side.

2. Core Compatibility Checks

• Meshing Clearance: Manually push the starter drive gear; the clearance between the gear and the flywheel ring gear must be 2–4mm (excessive clearance causes gear chipping, insufficient clearance leads to jamming).

• Voltage Verification: 12V starters are only for 12V single-battery systems. Connection to 24V dual-battery series systems is strictly prohibited.

• Gear Matching: Ensure the drive gear tooth count and module match those of the original flywheel ring gear. For Sisu, verify the engine model (e.g., D9/D12 light-duty series). For Ursus, check the tractor model (e.g., U450/U550). For Valtra/Valmet, confirm the starter part number corresponding to the model (e.g., Valmet 300/400 series, Valtra A series).

II. Brand-Specific Installation Steps (12V Dedicated)

(1) Installation of 12V Starter Motor for Sisu (Light Commercial Vehicles/Small Construction Machinery)

Location and Mounting Base Preparation

Pre-installation and Centering

1. Hoist the starter to the mounting seat and align the bolt holes. Temporarily screw in 2 mounting bolts (do not fully tighten).

2. Adjust the angle to ensure the drive gear axis is parallel to the flywheel ring gear axis.

3. Manually rotate the crankshaft to check that the gears mesh smoothly without jamming or uneven wear.

Bolt Tightening

Electrical Connection

• Main Power Supply: Connect the thick positive battery cable to the starter’s B+/+ main terminal. Install flat and spring washers, tighten to a torque of 20–25N·m, and apply conductive paste to the connector.

• Control Circuit: Connect the thin wire from the ignition switch to the solenoid’s S/50 auxiliary terminal. Wrap the connector with insulating tape.

• Grounding: Ensure the starter housing is properly grounded to the engine block. If grounding is poor, install an additional grounding cable with a cross-sectional area of ≥10mm² (smaller than required for 24V systems).

(2) Installation of 12V Starter Motor for Ursus (Small Tractors)

Mounting Base Preparation

Fixing and Centering

1. Small 12V starters typically use 2 mounting bolts. During pre-installation, adjust the position to ensure the drive gear can flexibly extend into the flywheel ring gear.

2. Manually toggle the gear to check smooth retraction.

Bolt Tightening

Electrical Connection

• Main Power Supply: Connect the thick positive battery cable to the B+/+ terminal, tighten to 20–25N·m, and apply conductive paste.

• Control Circuit: Connect to the output terminal of the tractor start switch. Secure the wiring firmly and keep it away from high-temperature components such as the exhaust pipe.

• Grounding: Ensure reliable grounding between the starter housing and the engine block. Install an additional grounding cable if necessary.

(3) Installation of 12V Starter Motor for Valtra/Valmet (Tractors/Agricultural Equipment)

Note: Valmet is the predecessor of Valtra. Installation specifications for 12V models are consistent, with the key difference lying in the mounting base layout (side-mounted for older Valmet models, bottom-mounted for newer Valtra models).

Mounting Base Preparation

• Older Valmet Models: The starter is mounted on the side flywheel housing mounting seat. Clean oil and rust and straighten deformed mounting bases.

• Newer Valtra Models: The starter is mounted on the lower flywheel housing mounting seat. Clean the mating surface and check for bushing wear.

Pre-installation and Centering

1. 12V starters mostly use 2 mounting bolts. After pre-installation, adjust the angle to ensure the meshing clearance between the drive gear and flywheel ring gear is 2–4mm.

2. Manually rotate the crankshaft to verify smooth gear meshing without jamming.

Bolt Tightening

Electrical Connection

• Main Power Supply: Connect the positive battery cable to the B+/+ terminal, tighten to 20–25N·m, and apply conductive paste.

• Control Circuit: Connect to the S/50 terminal of the start/ignition switch. Secure the wiring with cable ties to avoid interference with moving parts.

• Grounding: Ground the starter housing to the engine block/frame to ensure an unobstructed circuit.

III. Post-installation Commissioning (General)

1. Power Restoration: Reconnect the negative battery cable and check that no tools or debris are left around the starter.

2. No-load Test: Turn on the ignition switch and press the start button for ≤5 seconds per cycle. Observe that the starter runs smoothly without abnormal noise or smoke, and the drive gear extends and retracts freely.

3. Load Test: Start the engine and check for no gear meshing noise. The drive gear must retract quickly after engine startup. If cranking is weak, inspect for loose cable connections, insufficient battery voltage (≥12.4V static), or poor grounding.

IV. Key Precautions (12V-specific)

1. Power-off SafetyFor 12V single-battery systems, only disconnect the negative battery terminal. After power-off, wait 2–3 minutes to discharge residual power in the starter solenoid (shorter than the waiting time required for 24V systems).
2. Torque Control12V starters are compact with smaller-sized mounting bolts. Never exceed the specified torque limit, as over-tightening may cause thread stripping or bolt breakage.
3. Wiring Protection12V systems draw large starting currents (up to 200–400A). Use a main power cable with a cross-sectional area of ≥16mm². Ensure cable connectors are crimped tightly and coated with conductive paste to prevent overheating and ablation.
4. Anti-loosening MeasuresAgricultural/construction machinery operates under high-vibration conditions. Both spring washers and medium-strength threadlocker are mandatory for mounting bolts. Inspect bolts regularly for loosening.
5. Gear LubricationApply a small amount of high-temperature grease to the drive gear splines. Never inject oil into the solenoid or one-way clutch as this may cause internal component failure.

References：

I. OEM Official Manuals of Respective Brands (Core Basis)

1. Sisu

• Core Manuals: Sisu Workshop Manual - Electrical System (Light-duty Engine Volume, D9/D12 Light-duty Series), Sisu Engine Installation Manual

• Publisher: Sisu CV AB (Finnish Sisu Commercial Vehicle/Construction Machinery Company)

• Access Channels: Local authorized Sisu service centers/dealers, Sisu official service portal

2. Ursus

• Core Manuals: Ursus Tractor Service Manual (12V Small Tractor Models such as U450/U550), Ursus Electrical System Installation Standard

• Publisher: Ursus S.A. (Polish Ursus Tractor Company)

• Access Channels: Authorized Ursus service stations/parts centers in China, Ursus official website

3. Valtra/Valmet

   Note: Valmet is the predecessor of Valtra, and the installation specifications for 12V models are consistent.

• Valmet: Valmet Tractor Service Manual (12V Models of 300/400 Series)

• Valtra: Valtra Technical Manual - Starter Installation (Light-duty 12V Models such as A Series)

• Core Manuals:

• Publisher: Valtra Inc. (Finnish Valtra Agricultural Machinery Company, affiliated to AGCO Group)

• Access Channels: Valtra official website (https://www.valtra.com), authorized Valmet/Valtra dealers, AGCO technical service platform