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Volvo Penta MD21A Engine

General Technical Data

Engine Specifications

Engine Model ............... Volvo Penta MD21A
Engine Type ............... 4-cycle inline 4-cylinder indirect injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.54 (90.0)
Engine Stroke, in (mm) ............... 3.27 (83.0)
Displacement, cu.in (L) ............... 128.7 (2.11)
Rated Engine Power, hp (kW) ............... 75 (55) at 4500 rpm
Rated Engine Speed, rpm ............... 4500
Peak Torque ............... 116.8 Nm (86.1 lb-ft) at 2500 rpm
Idle Speed ............... 700-800 rpm
Aspiration Type ............... Naturally Aspirated
Operating Speed ............... 3000-4000 rpm
Compression Ratio ............... 22.1:1
Firing Order ............... 1-3-4-2
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Aluminum alloy
Lubrication System ............... Full-pressure
Oil Pump Type ............... Gear-driven
Oil Filter Type ............... Full-flow, spin-on
Cooling System ............... Liquid-cooled with heat exchanger
Water Pump Type ............... Belt-driven centrifugal fresh water pump and rubber impeller sea water pump
Air Cleaner Type ............... Replaceable element dry type or mesh silencer
Starting System ............... Electric Starter
Electrical System ............... 12V

Fuel System

Injection Pump Model ............... CAV Roto-Diesel DPA type
Injection Pump Type ............... Rotary distributor type
Governor Type ............... Mechanical or hydraulic built-in
Fuel Feed Pump Type ............... Diaphragm mechanical pump plunger activated
Fuel Injection Pressure, psi (bar) ............... 1958-2030 (135-140)
Injection Timing, degrees BTDC ............... 21
Injector Nozzle Type ............... Pintle nozzle type
Fuel Filter Type ............... Spin-on disposable cartridge with water separator separator element
Fuel Pre-Filter Type ............... Primary water separator sedimenter unit
Maximum Fuel Return Flow, gph (L/h) ............... 4.2 (16.0)
Fuel Tank Vent Diameter, in (mm) ............... 0.39 (10.0)
Fuel Supply Line Diameter, in (mm) ............... 0.31 (8.0)
Fuel Return Line Diameter, in (mm) ............... 0.23 (6.0)
Leak-off Pipe Type ............... Flexible copper or steel low pressure line
Cold Start Device ............... Glow plugs embedded inside pre-combustion chambers
Glow Plug Voltage, V ............... 12V
Glow Plug Current Draw, A ............... 15-20 per plug
Fuel Transfer Pump Pressure, psi (bar) ............... 4.4-7.3 (0.3-0.5)

Dimensions and Weight

Overall Length, in (mm) ............... 39.0 (990)
Overall Width, in (mm) ............... 23.6 (600)
Overall Height, in (mm) ............... 27.6 (700)
Dry Weight, lbs (kg) ............... 529 (240)
Wet Weight, lbs (kg) ............... 562 (255)

Maintenance Data

Service Information

Compression Pressure Test, psi (bar) ............... 298-341 (21.0-24.0)
Oil Pressure at Idle Speed, psi (bar) ............... 14.2 (1.0)
Oil Pressure at Full Speed, psi (bar) ............... 56.9-64.0 (4.0-4.5)
Thermostat Opening Temperature, F (C) ............... 167 (75)
Thermostat Fully Open Temperature, F (C) ............... 190 (88)
Alternator Belt Tension Deflection, in (mm) ............... 0.39 (10.0)
Intake Valve Clearance, in (mm) ............... 0.010-0.012 (0.25-0.30)
Exhaust Valve Clearance, in (mm) ............... 0.012-0.014 (0.30-0.35)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, SAE 15W-40
API Service Classifications ......................... CD or higher
Engine Oil Capacity with Filter, qt (L) ............... 5.81 (5.5)
Engine Oil Capacity without Filter, qt (L) ............... 5.28 (5.0)
Coolant Fluid Capacity, qt (L) ............... 9.51 (9.0)

Service Intervals

Change engine oil ............... Every 50 hours
Replace oil filter ............... Every 100 hours
Service air filter ............... Every 50 hours
Inspect seawater cooling ............... Every 100 hours
Replace impeller ............... Every 100 hours
Valve-lash adjustment ............... Every 100 hours
Check fuel system ............... Every 100 hours
Belt inspection ............... Every 100 hours

Service Specifications

Cylinder Bore Inner Diameter, in (mm) ............... 3.540-3.541 (90.000-90.015)
Cylinder Bore Maximum Wear Limit, in (mm) ............... 0.0039 (0.10)
Cylinder Bore Taper Limit, in (mm) ............... 0.0015 (0.04)
Main Bearing Clearance, in (mm) ............... 0.0019-0.0039 (0.05-0.10)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0015-0.0035 (0.04-0.09)
Crankshaft End Play, in (mm) ............... 0.0027-0.0098 (0.07-0.25)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0031-0.0047 (0.08-0.12)
Top Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.25-0.40)
Second Ring End Gap, in (mm) ............... 0.0078-0.0137 (0.20-0.35)
Third Ring End Gap, in (mm) ............... 0.0078-0.0137 (0.20-0.35)
Oil Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.25-0.40)
Top Ring Groove Side Clearance, in (mm) ............... 0.0027-0.0043 (0.07-0.11)
Second Ring Groove Side Clearance, in (mm) ............... 0.0019-0.0035 (0.05-0.09)
Third Ring Groove Side Clearance, in (mm) ............... 0.0019-0.0035 (0.05-0.09)
Oil Ring Groove Side Clearance, in (mm) ............... 0.0015-0.0031 (0.04-0.08)
Cylinder Head Flatness Maximum Distortion, in (mm) ............... 0.0019 (0.05)
Cylinder Block Surface Flatness Maximum Distortion, in (mm) ............... 0.0019 (0.05)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0011-0.0027 (0.03-0.07)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0019-0.0035 (0.05-0.09)
Valve Stem Maximum Wear Deflection Limit, in (mm) ............... 0.00078 (0.02)
Valve Face Angle, degrees ............... 45
Valve Seat Angle, degrees ............... 45
Camshaft End Play Clearance, in (mm) ............... 0.0019-0.0059 (0.05-0.15)
Camshaft Journal Clearance, in (mm) ............... 0.0011-0.0031 (0.03-0.08)
Rocker Arm Shaft Radial Clearance, in (mm) ............... 0.0007-0.0023 (0.02-0.06)

Tightening Torques

Cylinder Head Bolts (First Stage), lb-ft (Nm) ............... 29.5 (40.0)
Cylinder Head Bolts (Second Stage), lb-ft (Nm) ............... 51.6 (70.0)
Cylinder Head Bolts (Final Stage), lb-ft (Nm) ............... 51.6 (70.0)
Main Bearing Cap Bolts, lb-ft (Nm) ............... 59.0 (80.0)
Connecting Rod Cap Nuts, lb-ft (Nm) ............... 36.8 (50.0)
Flywheel Fastening Bolts, lb-ft (Nm) ............... 44.2 (60.0)
Crankshaft Front Pulley Attachment Nut, lb-ft (Nm) ............... 125.3 (170.0)
Camshaft Timing Gear Drive Bolt, lb-ft (Nm) ............... 25.8 (35.0)
Timing Gear Housing Casing Screws, lb-ft (Nm) ............... 18.4 (25.0)
Rocker Arm Shaft Assembly Support Bolts, lb-ft (Nm) ............... 29.5 (40.0)
Cylinder Rocker Valve Cover Nuts, lb-ft (Nm) ............... 5.9 (8.0)
Oil Pan Sump Drain Plug Drain Bolt, lb-ft (Nm) ............... 36.8 (50.0)
Oil Pan Sump Flange Housing Mounting Bolts, lb-ft (Nm) ............... 8.1 (11.0)
Fuel Injector Clamp Assembly Nuts, lb-ft (Nm) ............... 14.7 (20.0)
Fuel Injection Pump Drive Input Gear Nut, lb-ft (Nm) ............... 44.2 (60.0)
Fuel Pump Housing Body Bracket Fasteners, lb-ft (Nm) ............... 18.4 (25.0)
Fuel Injection High Pressure Line Union Nuts, lb-ft (Nm) ............... 18.4 (25.0)
Fuel Low Pressure Supply Pipe Banjo Fasteners, lb-ft (Nm) ............... 11.0 (15.0)
Glow Plugs Installation, lb-ft (Nm) ............... 14.7 (20.0)
Exhaust Manifold Collector Assembly Nuts, lb-ft (Nm) ............... 14.7 (20.0)
Intake Manifold Mounting Flange Bolts, lb-ft (Nm) ............... 14.7 (20.0)
Fresh Water Circulating Pump Housing Body Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Sea Water Impeller Pump Bracket Screws, lb-ft (Nm) ............... 14.7 (20.0)
Thermostat Housing Cover Screws, lb-ft (Nm) ............... 14.7 (20.0)
Oil Pressure Sensor Sending Unit, lb-ft (Nm) ............... 22.1 (30.0)
Coolant Temperature Sensor Sender Unit, lb-ft (Nm) ............... 22.1 (30.0)
Alternator Pivot Mount Bolt, lb-ft (Nm) ............... 36.8 (50.0)
Alternator Adjustment Lock Tensioning Bolt, lb-ft (Nm) ............... 18.4 (25.0)
Starter Motor Housing Mounting Flange Fasteners, lb-ft (Nm) ............... 36.8 (50.0)
Flywheel Housing Ring Adaptation Frame Bolts, lb-ft (Nm) ............... 36.8 (50.0)
Oil Filter Adaptation Nipple Thread Connector Bolt, lb-ft (Nm) ............... 22.1 (30.0)
Oil Pump Pickup Tube Screen Strainer Bracket Bolt, lb-ft (Nm) ............... 8.1 (11.0)
Oil Pump Internal Body Assembly Closure Screws, lb-ft (Nm) ............... 5.9 (8.0)
Crankcase Breather Valve Cap Assembly Nuts, lb-ft (Nm) ............... 5.9 (8.0)
Reverse Gear Marine Transmission Input Flange Nut, lb-ft (Nm) ............... 125.3 (170.0)

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