Engine Grade Camshaft Gear 3946436 – Overhaul Component for Cummins 4B3.9 6B5.9

Engine Sequence Variants Confirmed — We match this timing gear to your exact Cummins B-series or QSB build code before dispatch, preventing profile mismatches during overhaul.

Technical Specifications

Application Suitability

Why One Timing Gear Failure Often Means a Full System Teardown

Isolating a single gear replacement without checking the entire timing train invites rapid re-failure.

When a camshaft gear tooth shows abnormal wear, the root cause usually sits elsewhere in the system — oil starvation at the timing case, a worn idler gear shifting the mesh pattern, or a failing camshaft bushing allowing axial play. Replacing only the damaged gear leaves the underlying fault active. I have seen engines back on the stand within months because the rebuild addressed the symptom rather than the cause [NEED_CITE: timing gear train failure root cause analysis in medium-duty diesel engines]. A proper engine rebuild requires inspecting every mating surface in the timing drive before deciding what goes back in.

Timing System Context for Cummins B-Series and QSB Platforms

This camshaft gear sits at the center of the timing drive on Cummins 4B3.9, 6B5.9, and QSB5.9 engines. It meshes directly with the crankshaft timing gear below and transfers drive to the camshaft and fuel injection pump above. During an engine rebuild, the camshaft gear must be evaluated alongside its mating gears for backlash, tooth contact pattern, and axial runout. A camshaft gear replaced in isolation while the idler gear carries wear will develop uneven loading and accelerated tooth degradation.

Engine Serial Variants and Build Code Awareness

Cummins ISB CM2150 and CM550 builds can carry different timing gear profiles depending on production era and emission configuration. Ordering by engine family alone risks receiving a gear with incorrect tooth count or hub depth. Before confirming any timing component, the engine serial number and build code must be verified against the service manual timing section. We cross-check the serial range to confirm whether your engine requires the standard profile or a variant-specific camshaft gear configuration [NEED_CITE: Cummins ISB and QSB timing gear variant identification procedures].

Material Specification and Gear Accuracy

The 40Cr alloy steel construction provides the core hardness and fatigue strength needed for continuous timing drive duty. Zinc-nickel plating protects against corrosion during storage and initial run-in before full oil film establishment. ISO 1328-1 class 6 gear accuracy ensures tooth profile and pitch deviation remain within tight bounds, which directly affects mesh smoothness and noise levels at operating speed. The ±0.02 mm tolerance and <0.03 mm runout specification mean the gear mounts true to the camshaft axis, preventing the eccentric loading that causes premature bushing wear on the opposite end of the shaft.

What Happens When the Wrong Grade Goes In

Installing a timing gear without confirming the engine's rebuild history can introduce mismatched backlash. If a previous overhaul used oversize bearings or a reground camshaft journal, the gear mesh geometry shifts. The result is not immediate failure but a slow accumulation of tooth surface damage that surfaces as timing noise and eventually skipped teeth. This kind of fault is difficult to diagnose because it mimics injection timing problems [NEED_CITE: timing gear backlash effects on valve and injection synchronization]. Always pull the timing cover and measure existing clearances before ordering replacement components.

Sourcing With System-Level Accountability

Our own production lines and qualified partner facilities operate under a single warranty account, so every timing component in your overhaul carries identical quality terms. Eight product categories mean the camshaft gear ships alongside the timing cover gasket set, camshaft bushing, and front seal in one consignment — no split freight, no waiting on a second delivery. Minimum order is one piece, so a single replacement gear for a down machine moves as fast as a fleet overhaul kit. Guangzhou warehouse stock covers common B-series timing components for rapid dispatch. We identify parts from the engine serial number, a photograph of the nameplate, or the existing gear itself. Technical support is available to confirm compatibility and advise on matched replacement scope.

Documentation & Verification

• Commercial invoice listing each timing component by verified part number
• Cross-reference sheet mapping 3946436 to interchange numbers (reference only)
• Dimensional inspection record covering tooth profile and runout checks
• Warranty terms covering timing system defects for 3–12 months
• Packing photographs showing anti-rust coating and foam protection
• HS code and customs documentation for international engine parts shipment

Installation & Rebuild Sequence

• Clean timing case thoroughly and verify oil gallery flow before gear installation
• Check camshaft journal condition and bushing clearance before mounting the new gear
• Measure gear backlash against crankshaft and idler gears per service manual specification
• Confirm tooth contact pattern with marking compound after assembly
• Replace timing cover gasket set and front seal during the same rebuild cycle
• Run initial break-in at reduced load and re-check timing marks after first operating cycle

Request a Matched Timing Component Quote

Provide your engine model, serial number, and any known rebuild history so we can confirm the correct camshaft gear profile and recommend companion components for the timing system. If the nameplate is worn, a photograph of the existing gear or timing case casting number helps us verify fitment before you commit to a full overhaul order.

Frequently Asked Questions

Q: What other timing components should I replace along with the camshaft gear? A: During a timing system overhaul on Cummins B-series engines, we recommend inspecting the idler gear, crankshaft timing gear, camshaft bushing, and fuel pump drive gear for wear. The timing cover gasket set and front crankshaft seal should be replaced as standard practice. Replacing matched components together prevents early re-failure caused by a worn mating surface damaging the new gear.

Q: How do I confirm which camshaft gear fits my Cummins engine serial variant? A: Provide the full engine serial number and build code from the nameplate or dataplate. ISB CM2150 and CM550 variants may use different timing gear profiles. We cross-reference your serial against the manufacturer service data to confirm tooth count, hub depth, and mesh compatibility before dispatch.

Q: Is this gear included in a complete engine overhaul gasket kit? A: The camshaft gear is a hard part and is not included in gasket kits. However, we supply it alongside the timing cover gasket set, seals, and bearings as a consolidated overhaul package. This ensures all timing system components arrive together and carry the same warranty terms.

Q: What causes premature timing gear wear beyond the gear itself? A: Common root causes include oil starvation at the timing case, worn camshaft bushings allowing axial movement, misaligned idler gear shafts, and contamination in the lubrication system. Addressing these underlying faults during rebuild prevents the replacement gear from suffering the same damage cycle.