Yanmar 729649-51320 Fuel Injection Pump Assembly For 4TNV84 4TNV88 Engines

Yanmar 729649-51320 is the MP2-series mechanical fuel injection pump assembly specified for 4TNV84 and 4TNV88 direct-injection industrial diesel engines. This mono-plunger distribution pump meters and pressurizes fuel for delivery to each cylinder's injector through the hydraulic head, restoring factory fuel curves and combustion characteristics. It serves as the direct replacement for pumps exhibiting plunger wear, delivery valve leakage, or governor response degradation. The unit carries the eleven-digit Yanmar part number stamped on the aluminum pump body nameplate, alongside identification and manufacture date codes required for calibration and service parts lookup . Cross-reference coverage includes 72964951320, YM729649-51320, YM72964951320, and 729602-51310 for verification against the original unit .

The 4TNV84/4TNV88 engine pair powers an extensive range of compact equipment in North American and European fleets. Mini excavators from Yanmar, Takeuchi, and Gehl utilize these engines for their balance of power density and fuel efficiency. Skid steer loaders, compact wheel loaders, and tractor-loader-backhoes in rental fleets frequently run the 4TNV88 naturally aspirated variant. Mobile generator sets and refrigeration units rely on these engines for continuous-duty operation where injection pump reliability directly affects uptime guarantees. The 4TNV84T turbocharged version appears in applications demanding higher output from the same displacement, such as certain Landini and agricultural tractor platforms . Marine auxiliary applications also use TNV-series engines in vessels requiring dependable onboard power. For diesel parts distributors serving mixed-brand construction and agricultural accounts, maintaining coverage on this pump family reduces backorder exposure because the engine platform remains widely deployed despite newer emissions tiers entering the market.

Replacing the 729649-51320 demands more than mechanical aptitude-it requires disciplined adherence to Yanmar's timing procedure. Before pump removal, technicians must record the timing index number stamped on the original hydraulic head's engine-side boss and mark the pump flange-to-gear case reference position . The replacement pump arrives with its own timing index number; the algebraic difference between old and new values determines the injection timing offset applied during installation. Each graduation on the Yanmar timing sticker represents 0.5° of crankshaft timing change. The pump drive gear must align with the idler gear using the stamped reference marks-on 4TNV84/88 engines with the front gear case cover removed, the drive gear, idler gear, and crankshaft gear must all align at their respective timing marks . 

From a repair facility perspective, the 729649-51320 occupies a favorable position in the parts portfolio: high enough failure frequency to generate consistent demand, yet specialized enough to discourage generic substitutions. MP2 pump failures typically surface between 2,500 and 4,000 operating hours, with root causes clustering around fuel contamination (water ingress, microbial growth, degraded biodiesel) and neglected filtration . The trochoid charge pump is particularly vulnerable to abrasive particles because it operates on the low-pressure side before the main filter in some configurations. When a 4TNV84/4TNV88 engine presents with hard starting, white smoke at cold idle, or power fade under load, the injection pump is a prime diagnostic target after ruling out injector nozzle degradation. Shops that stock remanufactured units alongside new pumps capture price-sensitive customers without sacrificing margin on OEM-grade replacements. 

Q1: The replacement pump's timing index number differs from my original. How do I calculate the adjustment?
A: Subtract the original pump's index number from the replacement's index number. A positive result means the new pump requires advanced timing-rotate the pump away from the engine block by that number of graduations (each = 0.5°). A negative result requires retarded timing. Always verify with spill timing at cylinder No. 1.

Q2: Can this pump be used on both turbocharged and naturally aspirated 4TNV engines?
A: The 729649-51320 covers 4TNV84, 4TNV84T, and 4TNV88 applications. However, fuel delivery calibration differs between turbo and non-turbo variants. Verify the original pump's eleven-digit part number matches before installation.

Q3: What warranty documentation does your facility require for pump warranty claims?
A: Retain the installation invoice, fuel system inspection record (filter condition, water separator findings), and the engine's hour meter reading at installation. Warranty does not cover failures from contaminated fuel, improper timing, or operation with a restricted fuel filter.

Q4: Do you offer remanufactured pumps with core exchange?
A: Remanufactured 729649-51320 units are available. Core acceptance requires a complete, non-disassembled pump with intact mounting flange and drive gear interface. Core charges are refunded upon receipt of an acceptable unit within the specified return window.

Q5: What is the typical turnaround for a remanufactured pump exchange?
A: Standard remanufacturing lead time runs 5–7 business days after core receipt. Expedited programs may be available for fleet accounts. Contact your supplier for current availability and freight terms.

Q6: How do I identify whether my pump requires replacement versus recalibration?
A: Recalibration addresses governor drift and delivery quantity variance on a pump with intact plunger-to-barrel clearances. Replacement is indicated when ultra-low speed delivery tests show excessive leakage, or when the hydraulic head exhibits scoring or corrosion visible on disassembly .