Volvo Penta MD21A, MD32A, AQD21A, AQD32A Workshop Manual (P/N 2769 B)

• 42-page PDF reproducing the complete 40-numbered-page Volvo Penta workshop publication, plus its cover and introduction; identified as Pub. No. 2769 B, December 1975.
• Built around the MD21A, AQD21A, MD32A, and AQD32A, with separate data for the four-cylinder Indenor XDP 4/90 and six-cylinder XDP 6/90 engine families.
• Walks through major engine repair work from removal of electrical equipment, the combined intake/exhaust manifold, heat exchanger, sea-water and fresh-water pumps, fuel-injection pump, cylinder head, timing gear, camshaft, crankshaft, connecting rods, wet liners, and pistons through inspection and refitting.
• Documents cylinder-head repair, valve-guide and valve-seat work, liner-height checks, piston and ring installation, timing-gear assembly, crankshaft setup, and post-rebuild valve adjustment.
• Covers CAV Roto-Diesel/DPA injection-pump timing and test-bench setup, injector pressure and spray testing, feed-pump overhaul, glow-plug fault isolation, and final engine checks.
• Includes engine and instrument-panel wiring diagrams, a glow-plug troubleshooting table, component and cable-marking keys, and an engine fault-and-remedy chart.
• Supplies an illustrated 14-entry special-tool catalog plus torque tables, capacities, wear limits, fits, clearances, valve data, fuel-system settings, and lubrication specifications.

Engine Configurations and Repair Depth

This factory publication identifies the MD21A and AQD21A as four-cylinder XDP 4/90 engines and the MD32A and AQD32A as six-cylinder XDP 6/90 engines. Component-location plates show an MD32A with a Borg-Warner reverse gear and AQD21A/AQD32A installations with the 270D drive. Those views help identify the marine installation; the detailed repair instructions concentrate on the engine and its attached fuel, cooling, lubrication, starting, charging, and instrument systems. December 1975 is the publication date, not a blanket model-year claim for every covered engine.

The material is suited to marine-diesel technicians and experienced engine rebuilders who can use precision measuring equipment, dial indicators, pullers, valve-seat equipment, and diesel test-bench tooling. It is not written as a basic owner’s maintenance guide.

Internal Engine and Production Differences

The overhaul coverage goes well beyond disassembly. It addresses matched piston-and-liner assemblies, connecting-rod location and weight classes, crankshaft bearing checks, cylinder-head flatness inspection and grinding limits, prechamber handling, valve-seat geometry, guide replacement, and cold-engine valve adjustment after staged head-bolt tightening.

Production changes are called out where they affect repair choices. These include the later heat-exchanger lift-eye arrangement, the MD32 expansion-tank conversion, a revised vibration damper for MD32 engines above engine number 424673, and the requirement to use the late-production cylinder-head gasket whenever a liner has been replaced.

Fuel, Cooling, and Electrical References

Fuel-system data separates the four- and six-cylinder injection sequences and the settings for CAV Roto-Diesel/DPA pump types 4.90/4850 and 6.90/4350. The pump section describes engine indexing with a dial indicator, pump installation, test-bench fuel-flow adjustment, injector evaluation, and model-specific timing data without reducing the chapter to a list of measurements.

Named electrical and diagnostic references include the 4-cylinder engine with dynamo diagram, 4- and 6-cylinder engines with alternator diagram, early-production instrument panel schematic, late-production instrument panel schematic, glow-plug troubleshooting table, and final Troubleshooting Scheme for starting, stalling, low full-load speed, abnormal running, and overheating complaints.

Special Tools, Scope, and Repair Cautions

The two-page tool chart lists Volvo part numbers and model applicability. Examples include cylinder-liner extractor 884231, rear-main-seal tools 884232 and 884235, valve-guide tool 884236, CAV Roto-Diesel pump tool kit 884299, piston fitting ring 884309, and pump-adjustment valve tool 884473.

Two component-specific cautions matter during assembly and electrical testing. The crankshaft pulley must be fitted without damaging the sealing ring in the timing-gear case. The charging diagram also warns that opening the alternator-to-battery circuit while the engine is running can immediately ruin the charging-regulator diodes.

This workshop manual does not provide a separate overhaul section for the reverse gear or 270D drive. Oil grade and viscosity, fuel-system bleeding, and several boat, propeller, and outboard-drive checks are referred to the separate Instruction Book. Engine repair also involves heavy assemblies, rotating machinery, hot cooling components, and diesel injection equipment, so use appropriate lifting and test equipment and have safety-critical work handled by a qualified marine-diesel technician.