Q: What is the correct engine oil and capacity for the KTM 125? A: The KTM 125 Duke and RC require 1.5 Liters of high-quality 15W-50 semi-synthetic or full synthetic oil (JASO MA2 compliant, such as Motorex Formula 4T).

Q: What are the torque settings for the oil drain plug and filter cover? A: * Oil Drain Plug: 15 Nm

• Oil Filter Cover Bolts: 8 Nm

• Note: Always replace the O-rings when performing an oil change to prevent leaks.

Q: What is the spark plug and the correct gap? A: The standard spark plug is the BOSCH VR5NE (or equivalent NGK). The gap should be set to 0.8 mm (0.031 in).

Q: How much chain slack should a KTM 125 have? A: Chain slack should be between 5–7 mm when measured from the swingarm (refer to the wear indicator mark on the underside of the swingarm). If measuring the total vertical play in the center of the chain, aim for 25–30 mm.

Q: What are the valve clearance (tappet) specs for a cold engine? A: * Intake: 0.08–0.12 mm

• Exhaust: 0.13–0.17 mm

• Checking these is recommended every 7,500 km (4,650 miles).

Q: What is the coolant capacity and type? A: The system holds approximately 1.0 Liter. Use a silicate-free permanent anti-freeze (OAT technology) mixed 50:50 with distilled water.

Q: What are the standard tire pressures? A: * Front: 1.75 bar (25 psi)

• Rear: 2.0 bar (29 psi)

• Note: For high-speed riding or carrying a passenger, increase the rear to 2.2 bar (32 psi).

Essential Torque Specifications

Critical for safety and preventing stripped threads in the aluminum casings.

Component

Torque Setting (Nm)

Notes

Oil Drain Plug

15 Nm

Do not overtighten; uses a copper washer.

Oil Filter Cover

10 Nm

M6 bolts.

Front Axle Nut

45 Nm

43mm WP Forks.

Rear Axle Nut

90 Nm

Check chain alignment after tightening.

Spark Plug

12 Nm

Use a dedicated spark plug socket.

Brake Caliper (Front)

45 Nm

Radial mount bolts.

Rear Sprocket Bolts

35 Nm

Use Loctite 243 (Blue).

2. Fluids & Capacities

Based on the LC4c and standard Duke/RC single-cylinder engines.

• Engine Oil: * Capacity: 1.5L (Full change with filter).

  • Specification: SAE 15W-50 (or 10W-40) JASO MA2 (e.g., Motorex Formula 4T).

• Coolant: ~1.0L total. Use silicate-free permanent anti-freeze (50:50 mix).

• Brake Fluid: DOT 4 or DOT 5.1 (Never use DOT 5).

• Fork Oil: 450ml per leg (WP Apex 43mm). SAE 4W is the standard weight

. Tuning & Electrical Data

• Spark Plug: * Model: NGK LKAR8A-9 (Standard for Duke 125/200/390).

  • Electrode Gap: 0.8 mm – 0.9 mm.

• Valve Clearance (Cold Engine):

  • Intake: 0.08 – 0.12 mm.

  • Exhaust: 0.13 – 0.17 mm.

• Idle Speed: 1,400 ± 50 RPM (125/200) | 1,600 – 1,700 RPM (390).

• Tire Pressures (Solo): * Front: 29 PSI (2.0 Bar).

  • Rear: 29 PSI (2.0 Bar) — Increase to 32 PSI with a pillion.