<p><strong>Belt Tensioner 3976832 3911621</strong> — compatible with Cummins 4B3.9, 6B5.9, ISB, and QSB engine families. New aftermarket condition, ISO 9001 manufacturing standard.</p> <ul> <li>Part of the front-end belt drive system; matched supply with belts, idler pulleys, and associated seals ensures correct fit across engine serial variants</li> <li>Cross-reference interchange numbers 3937556, 3936207, 3911621, 3922901 verified for variant confirmation before overhaul</li> <li>Spring-loaded mechanism and pulley bearing evaluated at system level for B-series and C-series rebuilds</li> </ul> <p>Overhaul kit contents and matched components checked item by item against engine build requirements prior to dispatch.</p>
MOQ
1 Piece
Lead Time
2-5 Business Days
Shipping
120+ Countries
Warranty
3-12 Months
Compatible Brands
Overhaul Kit Verified — Cummins B-series and C-series tensioner cross-references checked against engine serial variants before dispatch.
| Parameter | Value |
|---|---|
| Part Number | 3976832 3911621 |
| Cross-Reference | 3937556, 3936207, 3934823, 3922901, 3973825, 3936208, 3934824, 3928748, 3279446, 4063951 (reference only) |
| Product Type | Belt Tensioner |
| Machine Fitment | 4B3.9, 6B5.9, 6C8.3, B5.9 G, ISB CM550, QSB5.9 CM850, 4BT3.9, 6BT5.9, ISB3.9, ISB4.5, QSB3.9, 6C, 6CT, 6CTA, 6CTAA, C8.3L, Hyundai R305LC-7, R290LC-7, HL757-7, HL740-9B |
| Condition | New Aftermarket |
| Warranty | 3–12 months against manufacturing defects |
| Certification | ISO 9001 |
| Engine System | Related Components |
|---|---|
| Front-End Belt Drive (4B3.9 / 6B5.9) | Drive belts, idler pulleys, fan hub assembly |
| Accessory Drive (ISB / QSB CM850) | Alternator bracket, water pump pulley, belt guard |
| C-Series Overhaul (6CT / 6CTAA) | Complete overhaul gasket set, crankshaft front seal |
| Hyundai Excavator Powertrain (R290LC-7 / R305LC-7) | Fan drive belts, coolant hoses near belt path |
The tensioner rarely fails alone — worn pulleys and fatigued belts create the load that kills it.
In Nigerian mining camps I have pulled apart ISB and 6B5.9 engines where a fresh tensioner was bolted onto a glazed pulley, and the new unit was squealing within two weeks. The root cause sits in the surrounding belt drive components: a scored idler bearing introduces lateral runout that the spring mechanism cannot absorb, and an old belt that has taken a permanent set demands more travel than the tensioner arm was designed to provide. Rebuilding shops that treat the belt drive as a system rather than a single-line item see noticeably fewer comebacks [NEED_CITE: belt drive system maintenance practices for heavy-duty diesel engines].
This Belt Tensioner for Cummins engine rebuild belongs to the front-end accessory drive on B-series and C-series powerplants. It maintains correct belt deflection across the alternator, water pump, and fan circuits simultaneously. When planning a rebuild, sourcing the tensioner alongside matched belts and inspected idler pulleys keeps the entire front-end drive within tolerance from first startup.
Cummins released multiple tensioner configurations across the 4B3.9, 6B5.9, ISB, and QSB families. Pulley diameter, spring rate, and arm pivot geometry differ between early and late serial ranges, and a superseded number does not always drop into the same mounting pattern. Confirming the exact engine serial number against the build sheet prevents the situation where the tensioner physically bolts on but applies the wrong load to a narrower belt profile [NEED_CITE: Cummins B-series and C-series belt drive configuration differences].
The spring-loaded mechanism inside this tensioner must deliver consistent radial force across its full travel range; a weak spring allows belt slip under high alternator load, while an over-tensioned unit accelerates water pump bearing wear. Pulley runout directly affects belt tracking — even minor lateral movement causes the belt to walk off the rib profile at high RPM. The bearing sealed inside the pulley must withstand continuous thermal cycling from the adjacent fan airstream and radiant heat from the exhaust manifold on compact B-series installations.
Replacing the tensioner in isolation on an engine that has already seen one overhaul cycle leaves worn idler bearings and stretched belts in place. The new tensioner compensates for the existing slack and travel mismatch, working outside its designed range from day one. Within a short service period the spring fatigues prematurely or the pulley bearing fails under the irregular load, and the machine is back in the workshop for the same complaint [NEED_CITE: diesel engine belt drive repeat failure analysis].
Production lines and qualified sourcing partners operate under one warranty account, so the tensioner ships alongside matched belts, gaskets, and idler components without warranty gaps between suppliers. Eight product categories mean a complete overhaul kit consolidates into a single consignment. Orders start from one piece for emergency rebuilds. Cross-reference verification covers superseded numbers across the full Cummins reference chain listed above. A technical team confirms the correct tensioner variant against your engine serial number and rebuild history before the order is finalized.
Provide your Cummins engine model, serial number, and any previous overhaul records so the correct tensioner variant is confirmed against the build sheet. Include the full list of belt drive components you need replaced so everything ships matched in one consignment.
Q: What other belt drive components should be replaced at the same time as the tensioner? A: Idler pulleys, drive belts, and the fan hub bearing should all be evaluated during the same service event. Worn idler bearings introduce runout that shortens tensioner life, and belts that have taken a permanent set demand travel the new unit cannot provide long-term. Matching these components in one order keeps the entire front-end drive within specification.
Q: How do Cummins engine serial variants affect which tensioner number applies? A: The 4B3.9, 6B5.9, ISB, and QSB families use different pulley diameters and spring rates across production runs. A superseded reference number may not match the mounting geometry of a later serial range. Supplying the full engine serial number allows the correct variant to be confirmed before the order is processed.
Q: Can I order a complete belt drive service kit including belts, pulleys, and hardware together? A: Yes. The belt drive system components ship in a single consignment under one warranty. Consolidating the tensioner, belts, idler pulleys, and associated fasteners into one order prevents compatibility gaps and avoids split shipments arriving at different times.
Q: My engine was previously rebuilt — how do I confirm the correct tensioner variant? A: Previous rebuilds may have introduced non-standard components or altered the accessory drive configuration. Provide the engine serial number along with any available rebuild records or photographs of the existing belt drive layout so the tensioner variant can be matched to what is actually on the engine.
Q: What inspection data is provided to confirm the tensioner meets specification before shipping? A: Each unit is checked for pulley runout, spring tension across full arm travel, and bearing smoothness before dispatch. The inspection record accompanies the shipment so the receiving workshop can verify the tensioner was within tolerance at the point of packing.
<p><strong>Overhaul kit contents verified item-by-item</strong> against your specific engine serial build before dispatch.</p>
View Details<p><strong>6718730 Fan Belt</strong> — engine cooling system replacement for Bobcat 5600, 773, S150–S205, T180–T190 skid steer loaders. High-tensile polyester cords with heat-resistant rubber compound sustain continuous flexing under heavy load.</p> <ul> <li>Inspect tensioner, idler pulley, and fan clutch at belt replacement to address root cause of failure rather than repeat it</li> <li>Confirm engine serial to verify correct belt variant and avoid mismatched drive components</li> </ul> <p>Matched belt and tensioner sets shipped together for complete cooling system service.</p>
View Details<p><strong>Belt Tensioner Assembly 7167165 7274780 7273503, 6061-T6 Aluminum Pulley with PTFE Bronze Bushing</strong> — replacement for Bobcat S510–T870 skid steer and track loaders.</p> <ul> <li>Part of the engine belt drive system; matched tolerances across pulley, spring, rocker arm, and bushings prevent repeat slippage failures</li> <li>Pulley runout within ±0.02 mm; spring preset to 180–220 N for consistent tension under high-torque cycles</li> </ul> <p>Overhaul kit contents verified item-by-item before dispatch to match your engine build.</p>
View Details<p>Stop downtime and noise from slipping or squealing drive belts — this <strong>bobcat drive pump belt</strong> delivers quiet, slippage-free power transfer even under heavy loader cycles. Built for real-world reliability, it replaces OEM part 6736775 with precision fit and proven durability across Bobcat S150, S175, S205, T190, and Toolcat 5600 models.</p> <ul> <li><strong>Flat, 3-groove cogged design</strong> eliminates harmonic vibration — no more high-frequency whine during hydraulic pump engagement</li> <li>Fiber-loaded backing + dual-cord reinforcement reduces heat buildup and extends service life beyond standard EPDM belts</li> <li>Exact OEM dimensions: 58.15″ L × 1.19″ W — critical for proper tension and pulley alignment on compact loader drive trains</li> <li>Ships same-day from our Guangzhou warehouse — no waiting weeks for OEM backorders</li> </ul>
View DetailsSend us your inquiry and our technical team will verify the part and provide a competitive quote within 24 hours. MOQ starts from 1 piece.
Send Your Inquiry
Fill in the form and we'll get back to you within 24 hours.
