Royal Enfield 143907 – Chaincase Outer (Front Half, Inches Thread) for Old Bullet 350 / 500, Electra, Machismo, Lightning, Thunderbird (Pre-March 2002, 4-Speed)

Royal Enfield part 143907 is the genuine “CH.CASE FRONT HALF STD / Chaincase outer (Inches)” used as the outer primary chaincase cover on classic cast-iron and early AVL Bullets and derivatives built up to March 2002 with imperial-thread chaincase hardware. Royal Enfield’s retired-models parts catalogue lists 143907 as “Chaincase outer (Inches)” for a wide range of CI models (Std, Deluxe, Machismo, Campus, Electra, Bullet 500, Lightning, Machismo A-series, Thunderbird) with a remark: “Before Mar ’02”, after which it is superseded by metric and CDI-specific chaincases.

Bike-Parts-RoyalEnfield and multiple dealer price lists confirm 143907 / CH.CASE FRONT HALF STD as an OEM part, while Hitchcocks describe it as “CHAINCASE, OUTER (Imperial threads fitted up to March 2002)”, reinforcing the date and thread-type boundary. Sellers like Recart and The Spares Company label it as chaincase outer for “OLD model, 1980–2009” Bullets and list Bullet 350, Deluxe, Machismo, Campus, Bullet 500 among confirmed users.

This cover forms the right-side primary case enclosing the engine sprocket, primary chain and clutch. A damaged or leaking primary cover can cause oil loss, noisy running and poor appearance. Replacing it with a genuine 143907 ensures correct sealing surfaces, screw pattern and imperial threads, avoiding the headaches of mixing inch and metric hardware.

⚠️ Important: 143907 fits imperial-thread primary chaincases only (pre-March 2002). Later metric/CDI/TCI and UCE / J-Series engines use different chaincase designs and are not compatible.

Key Features 

• Genuine Royal Enfield primary chaincase outer – OEM part no. 143907, described in RE catalogues as “CH.CASE FRONT HALF STD / Chaincase outer (Inches)”.

• Designed for cast-iron & early AVL Bullets with imperial-thread primary cases produced up to March 2002.

• Forms the front/outer half of the primary chaincase, enclosing primary chain, clutch and engine sprocket.

• Correct bolt pattern, profile and depth for stock 4-speed primary layout – no cutting, drilling or bracket jugaad on compatible bikes.

• OEM-grade pressing and finish for proper sealing with the matching crankcase-to-chaincase gasket and oil level plug.

• Ideal for restoring leaking, cracked or over-welded primary cases on old Bullets where oil seepage and misalignment are common.
  

• Supplied as chaincase outer only – internal components, gaskets and fasteners sold separately, allowing you to reuse good existing parts.

Compatibility Table 

Platform rule:

• ✅ Fits CI / early AVL models with imperial-thread primary chaincase, built up to March 2002.

• ❌ Does not fit later metric-thread chaincases, CDI/TCI-only versions, UCE or J-Series engines.

✅ Confirmed Applications (per RE retired-models catalogue & specialist dealers)

PLEASE CHECK PART NUMBER BEFORE PURCHASE 

❌ Explicit Exclusions

• All UCE models: Classic 350/500 UCE, Bullet 350 UCE, Electra UCE, Thunderbird UCE.

• All J-Series: Classic Reborn, Hunter 350, Meteor 350, new Bullet 350 J.

• 650 Twins (Interceptor / Continental GT), Himalayan 411 / 450, Scram 411, Guerrilla 450 etc.

• Later machismo / Electra / Thunderbird where RE or aftermarket explicitly warn: “not for Machismo, Thunderbird, Electra and other lean burn models” – those use metric/CDI cases.

Variants

This listing covers one OEM variant:

• Part Number: 143907

• Description: Chaincase outer / CH.CASE FRONT HALF STD – inches thread

• Finish: Typically polished or painted alloy/steel primary cover (appearance can vary slightly by production batch; check product photos)

• Position: Right side – outer half of primary chaincase

• Quantity: 1N (primary outer cover only)

FAQs 

Q1. How do I know if my bike needs the “inches” chaincase (143907) or a metric one?
If your Bullet / Thunderbird / Lightning is pre-March 2002 and still running its original primary, it most likely uses imperial-thread chaincase hardware and in many cases 143907. Later bikes changed to metric fasteners and CDI-specific cases (e.g., 144917/4, 145464/1). The safest check is your parts book or existing chaincase part number, or measuring the thread of the primary cover screws.

Q2. Will 143907 fit my Electra / Machismo / Thunderbird?
It depends on year and engine type. RE’s retired catalogue shows 143907 used on several early CI/AVL variants, but many modern sellers clearly warn that it will not fit later lean-burn Electra / Machismo / Thunderbird models with metric and CDI/TCI cases. If your bike is post-2002 or labelled “lean burn/AVL CDI”, treat fitment as unlikely and confirm with a parts manual or RE dealer before ordering.

Q3. Does this chaincase outer come with gaskets, oil plugs, or screws?
No. Part 143907 is only the outer chaincase cover/front half. You must purchase or reuse the gasket, inspection/oil filler plugs, fiber washers and mounting screws separately (they carry different part numbers in the primary chaincase diagram).

Q4. Can I use 143907 on a UCE Bullet or Classic Reborn?
No. UCE and J-Series engines have a completely different unit-construction primary and gearbox layout, so the old separate chaincase outer will not fit. This part is strictly for older CI/AVL “separate gearbox” Bullets with primary drive on the right.