Royal Enfield Liquid Gun 10W50 Fully Synthetic Engine Oil 1L – Interceptor 650 / Continental GT 650 – Part 3900105

Royal Enfield part 3900105 is the genuine Liquid Gun 10W50 Fully Synthetic Engine Oil – 1 litre pack, developed for the 650 Twin platform. Royal Enfield’s official technical specifications for the Interceptor 650 and Continental GT 650 clearly recommend fully synthetic 10W-50 engine oil to API SL (or higher), JASO MA2 for optimum lubrication and clutch performance. In the factory parts list for the 650 parallel-twin engine, 3900105 is listed as “10W50 API SL Engine Oil – 1 Litre”.

This 1L pack of Liquid Gun 10W50 is ideal for authorised-grade oil changes on Interceptor 650 and GT 650, especially if you prefer to use OEM-branded oil instead of third-party brands. The fully synthetic formulation is designed to handle sustained high RPM, hot climates, traffic, and touring loads, while keeping the engine internals cleaner and protecting the slip-assist clutch.

A full oil change on the 650 Twins typically requires about 3.1L, which means most riders buy 4 x 1L cans (3900105) for one service and retain the remaining oil for top-ups. For riders who care about warranty, sticking to the correct 10W50 API SL / JASO MA2 specification is critical.

Note: This listing is specifically optimised for Interceptor 650 and Continental GT 650 (BS4 & BS6) where 10W50 fully synthetic is the factory-recommended grade. It is not the correct grade for 350 UCE/J-Series or Himalayan 411 engines, which typically require 15W50.

Key Features 

• Genuine OEM Royal Enfield part 3900105 – 10W50 API SL fully synthetic engine oil, 1 litre pack.

• Correct grade for 650 Twins – matches factory spec for Interceptor 650 / Continental GT 650: Fully Synthetic 10W-50, API SL (or higher), JASO MA2.

• Designed for high-performance parallel-twin engines – supports sustained highway speeds, spirited riding, and high ambient temperatures without viscosity breakdown.

• Fully synthetic formulation – superior film strength and thermal stability vs mineral or semi-synthetic oils, helping reduce wear on cams, pistons, rings and bearings.

• Wet-clutch compatible (JASO MA2-grade) – ensures proper clutch engagement on the 650 Twins’ slipper-assist clutch system and smooth gearshifts.

• OEM grade for warranty-friendly maintenance – uses the same viscosity and performance category referenced in Royal Enfield documents and recommended by dealers for 650 Twins.

• Ideal for DIY servicing – 1L can with clear labelling, convenient for at-home oil changes or top-ups between scheduled services.

• Cleaner engine over time – synthetic base oils and detergent additives help control deposits and sludge, especially important for long-interval oil changes on 650 Twins.

Compatibility Table

Engine platform: 650cc Parallel Twin (Royal Enfield)

Evidence of association with 650 Twin engines: In the Royal Enfield INT 650 Euro IV microfiche, 3900105 is listed under the 650cc parallel-twin engine section as “10W50 API SL Engine Oil – 1 Litre” together with the 50L workshop drum 3900104. The RE price list also lists 3900105 = 10W50 Engine Oil 1 litre as a standard spare item.

Not for: Classic/Bullet/Thunderbird 350/500 UCE, J-Series 350s, Himalayan 411, Scram 411, Super Meteor 650 or Himalayan 450 – these platforms typically specify 15W50 or 10W40 grades from the factory, not 10W50 Liquid Gun.

Variants

• Pack Size:

  • 1 x 1 Litre can – Part No. 3900105 (this listing)

FAQs 

Q1. Is this the correct Royal Enfield oil for Interceptor 650 and Continental GT 650?
Yes. Royal Enfield’s official technical spec for the 650 Twins calls for fully synthetic 10W-50 engine oil to API SL (or higher), JASO MA2. Liquid Gun 10W50 in the 1L pack (part 3900105) is the OEM grade designed around that requirement.

Q2. How many litres do I need for a full oil change on my 650 Twin?
The Interceptor 650 and GT 650 generally require about 3.1 litres for a routine oil change, and around 3.9 litres for a first dry fill. Practically, most riders buy 4 x 1L cans (4 litres total) and keep the unused oil for top-ups.

Q3. Is Liquid Gun 10W50 fully synthetic or semi synthetic?
Liquid Gun 10W50 (3900105) is marketed and sold as a fully synthetic engine oil, distinct from the 15W50 Liquid Gun semi-synthetic blend used in many 350cc models.

Q4. Can I use this 10W50 oil in my Classic 350, Bullet 350 or Himalayan 411?
Officially, most Royal Enfield 350 UCE and J-Series engines, and the Himalayan 411, specify 15W50 (often Liquid Gun 15W50 semi-synthetic). While some riders experiment with 10W50, using a grade different from what’s in the manual can impact warranty and is not generally recommended.

Q5. Will using non-OEM oil void my warranty?
Royal Enfield primarily cares that the oil meets the required grade and specification (10W-50, API SL or higher, JASO MA2) and that service intervals are followed. However, using genuine Liquid Gun 10W50 (3900105) keeps your maintenance completely aligned with OEM expectations and avoids arguments with service centres.