Komatsuengine(no series)

Komatsu 3D68E-3B(S/N 00101-UP)

Maintenance schedule, common problems & OEM parts breakdown

Search live 3D68E-3B(S/N 00101-UP) parts

The Komatsu 3D68E-3B is a naturally aspirated, indirect-injection 3-cylinder diesel built for Komatsu's smallest conventional mini excavators. It belongs to Komatsu's 68E-88E engine series, a family spanning the 2D68E, 3D68E, 3D74E, 3D78AE, 3D82AE, 3D82E, 3D84E, and 3D88E three-cylinder engines plus the 4D82E/4D84E/4D88E four-cylinder derivatives used across Komatsu's compact excavator and industrial equipment lines. Displacing roughly 0.78 liters (a 68 mm bore and 72 mm stroke), the -3B build (serial number 00101-UP) is the confirmed engine for the Komatsu PC05-7 mini excavator, rated around 10.3 kW (13.8 hp) at 2400 rpm on the general-use governor setting. The host machine runs roughly 1.2 to 1.4 tonnes (2,650 to 3,090 lb) operating weight, varying by production year and configuration, with the wider family of 3D68E-powered mini excavators (spanning roughly the PC05-7 through PC20FR-1 class) covering a broader sub-1-tonne to 2-tonne range. It uses a mechanical governor, gear-driven camshaft, and a glow-plug cold-start system, with no turbocharger and no emissions aftertreatment.

Later machines in this engine family carry the 3D68E-3G, 3D68E-3H, and 3D68E-3K engine codes at a separate, later serial break, fitted to a different set of Komatsu mini-excavator hosts than the PC05-7 covered here — a broader generational step within the same 3-cylinder architecture rather than a documented direct changeover on this specific chassis. Because the 3D68E core design is shared with the Yanmar 3TNE68, rebuild kits, gaskets, and wear parts stay easy to source even though Komatsu stopped building this excavator generation decades ago. That parts commonality, paired with a simple mechanical fuel system and no onboard electronics to fail, keeps these small excavators attractive on the used market to owner-operators and rental fleets who want a rebuildable machine rather than a disposable one.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.

Komatsu 3D68E-3B(S/N 00101-UP) specifications

Engine

Engine model	3D68E-3B (S/N 00101-UP), factory-fitted to the Komatsu PC05-7 mini excavator
Type	Vertical, 4-cycle water-cooled diesel, 3 cylinders
Combustion system	Indirect injection, special swirl pre-combustion chamber
Bore x stroke	68 x 72 mm
Displacement	0.784 L (47.8 cu in)
Rated output	10.3 kW (13.8 HP) at 2400 rpm, general-use (VM) governed application
Output range across governed speed settings	8.6 kW (11.5 HP) at 2000 rpm up to 12.9 kW (17.3 HP) at 3000 rpm, per governed speed setting selected for the application
Compression ratio	23:1
Governor	Mechanical centrifugal, all-speed type
Starting system	Electric
Emissions tier	Not documented for this pre-regulation era serial range

Weights

Operating weight (host machine, PC05-7)	1.2 t to 1.4 t, varies by production year/configuration
Engine dry weight	70 kg with back plate, 81 kg with flywheel housing
Ground pressure	Not documented for this exact serial range — verify with your dealer

Dimensions

Engine overall dimensions (L x W x H)	463.5 x 401 x 496 mm with back plate, 473.5 x 401 x 496 mm with flywheel housing
Host machine transport width	0.96 m to 1.0 m, varies by production year/configuration
Host machine track/undercarriage width	230 mm
Bucket capacity (host machine)	0.03 to 0.07 m3, varies by bucket fitted
Transport length/height	Not documented for this exact serial range — verify with your dealer

Performance

Travel speed	Not documented for this exact serial range — verify with your dealer
Swing speed	Not documented for this exact serial range — verify with your dealer
Digging depth / reach	Not documented for this exact serial range — verify with your dealer
Governing performance	Steady-state speed band and recovery time meet the factory general-use (VM) governor class for this engine platform

Service capacities (summary)

Fuel tank	Not documented for this exact serial range — verify with your dealer
Hydraulic system	Not documented for this exact serial range — verify with your dealer
Engine oil (lubrication)	2.4 L maximum, 1.0 L effective (dipstick-to-full working range)
Cooling system	0.9 L, engine circuit only (radiator circuit not included)

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

3D68E-3B(S/N 00101-UP) fluids & capacities

System	Capacity	Recommended fluid
Engine crankcase (with filter)	2.4 L maximum, 1.0 L effective dipstick-to-full range (2.5 US qt maximum, 1.1 US qt effective)	Komatsu Genuine EO diesel engine oil, API CD/CF-class. SAE 15W-40 for temperate climates, SAE 10W-30 for cooler regions, and a low-ash arctic grade for sustained cold down to about -30°C (-22°F). Match viscosity to seasonal ambient temperature per the standard Komatsu oil-viscosity chart.
Cooling system	0.9 L (1.0 US qt), engine circuit only — full-system total including radiator is not documented for this exact serial range	Komatsu Super Coolant (ethylene-glycol, corrosion-inhibited, all-season type), premixed to the local freeze-protection requirement. Do not mix coolant types.
Fuel tank	Not documented for this exact serial range — verify with your dealer	No. 2-D diesel fuel (ASTM D975 equivalent) for normal use; switch to No. 1-D or a winter-blend diesel in cold weather below roughly -1°C (30°F) to prevent fuel waxing.
Hydraulic system (tank and circuit)	Not documented for this exact serial range — verify with your dealer	Komatsu Genuine HO-series anti-wear hydraulic oil, SAE 10W equivalent for normal ambient range; a low-viscosity cold-climate hydraulic grade where sustained sub-zero starts are expected.
Travel and swing drives	no standalone refill capacity documented for this engine's host machines	Not applicable as a separate service point. On this excavator class the travel/swing motors are sealed hydrostatic units integrated with the main hydraulic circuit; no independent gear-oil change interval is published. Confirm with the host-machine OMM.
Transmission / powertrain compartment	not applicable	Not applicable. This engine powers hydrostatically-driven mini-excavator hosts with no mechanical transmission or gearbox requiring a separate fluid fill.
Grease points (pins, bushings, linkages)	per-point service, no bulk reservoir capacity specified	Komatsu Genuine multipurpose lithium-base grease (G2-LI type), applied at scheduled greasing intervals.

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Komatsu 3D68E-3B(S/N 00101-UP) maintenance schedule

Service interval	Tasks
Every 50 h	Check engine oil level before starting each shift and top up as needed. Check coolant level in the radiator and reservoir; inspect for external leaks. Drain water and sediment from the fuel filter/water separator. Inspect fan belt tension and condition. Walk around the engine and hose fittings checking for fuel, oil, or coolant seepage. Clean the air cleaner element more often when working in dusty conditions.
Every 250 h	Change engine oil and replace the oil filter cartridge. Inspect and clean (or replace) the air cleaner element. Check battery electrolyte level and clean/tighten terminal connections. Inspect glow plug wiring and connector points for corrosion. Check undercarriage track tension and grease idlers and rollers.
Every 500 h	Replace the fuel filter cartridge. Check and adjust fan belt tension. Change the hydraulic oil filter element. Inspect injector spray pattern if cold starting has gotten harder or exhaust smokes. Check oil level in travel/swing reduction gear cases. Clean radiator fins and inspect coolant hoses for hardening or cracking.
Every 1,000 h	Check and adjust intake and exhaust valve clearance. Replace the hydraulic tank breather element and return filter. Check fuel injection timing. Inspect starter motor and alternator brushes and connections. Change oil in travel and swing reduction gear cases.
Every 2,000 h	Replace hydraulic system oil. Check and reset fuel injection pump delivery. Test the glow plug relay/timer and charge indicator circuit. Check cylinder head bolt torque and inspect for head gasket seepage. Inspect injector nozzles as a set for wear at the swirl-chamber tip.
Every 4,000 h	Inspect or replace the water pump and thermostat. Check crankshaft end play and main/rod bearing clearance if oil pressure has dropped. Overhaul or replace the fuel injection pump. Inspect cylinder liners, pistons, and rings for wear ahead of a top-end rebuild. Replace engine mounts and vibration dampers.
Every 6,000 h	Plan a full in-frame overhaul: pistons, rings, liners, and main bearings. Resurface or replace the cylinder head if repeated warpage has been logged. Rebuild the gear-driven camshaft train and inspect timing gear backlash. Replace all engine seals and gaskets as a set during teardown.

Servicing the 3D68E-3B(S/N 00101-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

The 3D68E-3B carries no ECM or fault-code system, so condition monitoring rides on scheduled oil sampling and visual inspection instead of diagnostics. Pull an oil sample at every oil change and track wear-metal trends — the small 3-cylinder sump concentrates contamination faster than a larger block. Watch exhaust smoke color for early injector or swirl-chamber wear, and check coolant condition given the compact radiator's limited reserve. Hard cold starts or a new injector knock are early warning signs worth logging before they become a repair.

Corrective & Common Repairs

Most field calls on this engine trace to electrical accessories rather than the block: glow plug relay, current limiter, and charge indicator circuits are recurring failure points behind hard starting or charging complaints. Injection pump and nozzle wear from swirl-chamber carbon buildup shows up as rough idle or white smoke. On the excavator side, expect rubber-track roller and idler wear from the compact undercarriage, plus hydraulic relief-valve drift that slows bucket and swing cycle times as the machine ages.

Overhaul & Rebuild Points

Overhaul work on the 3D68E-3B centers on the swirl-chamber prechamber and glow plug bore, which erode faster than the cylinder itself on this indirect-injection design. Check liner and ring wear, crankshaft main and rod bearing clearance, and backlash in the gear-driven camshaft train. Cylinder head warpage from overheating is a recurring rebuild finding — resurface or replace rather than shim it. Because the block shares tooling with the Yanmar 3TNE68, overhaul gasket sets and piston kits remain easy to find.

Seasonal & Environment Servicing

This naturally aspirated, indirect-injection 3-cylinder is a notoriously hard cold-starter without a healthy glow plug system — test the glow plugs and relay/timer circuit before winter and keep the battery at full charge. In hot or dusty jobsite conditions, step up air cleaner and radiator fin cleaning since the small-capacity radiator has little thermal margin. Drain fuel filter water more often through wet-season use, and confirm coolant antifreeze concentration before freezing weather to protect the compact cooling jacket.

3D68E-3B(S/N 00101-UP) common service parts

Part number	Part	Notes
YM119255-55620	Fuel Filter Ass'Y	Fuel system service	Check fitment →
YM102103-55520	O-Ring,(For Fuel Filter)	Fuel system service	Check fitment →
YM124550-55700	Element,Fuel Filter	Fuel system service	Check fitment →
YM171051-92760	Wrench,Fuel Filter? Water Separator	Fuel system service	Check fitment →
YM121465-12510	Element,Air Cleaner	Air intake service	Check fitment →

Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.

3D68E-3B(S/N 00101-UP) attachments & work tools

Digging buckets

Standard trenching buckets for this engine's confirmed host, the Komatsu PC05-7 mini excavator, and similarly sized machines in Komatsu's wider micro-excavator class run roughly 200-400 mm wide with capacities around 0.03-0.06 m3, varying by exact model and dipper geometry. Pin-on mounting is standard; no factory quick-coupler is fitted at this size class.

Grading/ditching buckets

Wider, flatter buckets are offered for backfilling and light grading on the same pin-on mount as the digging bucket. Width and capacity scale with the host model within this micro-excavator range and are not interchangeable across differently sized siblings without confirming dipper pin spacing.

Dozer/backfill blade

A front-mounted angling or straight blade is standard or factory-optional across this class, used for backfill, leveling and machine stabilization during digging. It runs off the base hydraulic circuit (its own blade cylinder), not an auxiliary attachment line.

Hydraulic breaker/hammer

Light-duty breakers sized for this weight class are supported as an option but require an auxiliary one-way hydraulic piping kit that is either factory-fitted or dealer-retrofitted to the arm; machines without the kit cannot run a breaker without added plumbing.

Auger

A small-diameter earth auger is an available work tool on models in this range, also requiring the auxiliary hydraulic piping kit noted above. Size/torque capacity is limited by the machine's small pump output and is not documented in detail for this exact serial range; verify with your dealer.

Mounting/coupler system

Bucket and attachment mounting on this micro-excavator class is pin-on; a factory hydraulic quick-coupler is not typical at this size, so tool changes are done manually with mounting pins.

Undercarriage and operator guarding

Rubber crawler tracks are standard across this size class for surface protection, and a TOPS-rated canopy is the usual factory operator guard, with an enclosed cab offered on some machines in the wider class. Some sibling machines in this engine-family class use zero- or reduced-tail-swing / retractable-track configurations for confined-space work rather than a bolt-on attachment.

All 3D68E-3B(S/N 00101-UP) assemblies by section

Every catalogued assembly group for the Komatsu 3D68E-3B(S/N 00101-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Cooling System

Komatsu : 3d68e-3b(S/N 00101-Up) : Cooling System : Water Pump And Cooling Fan

YM***00	Water Pump Ass'Y	1
YM***20	Gasket (Kit)	1
YM***91	V-Belt	1
YM***52	Screw	3

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Cylinder Block

Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Camshaft And Tappet

YM***00	Tappet	6
YM***50	Retainer, Bearing	1
YM***22	Screw	2
YM***00	Rod,Push	6

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Crankshaft

YM***00	Gear,Crank	1
YM***80	Bolt	1
YM***41	Washer	1
YM***80	Pulley,Crank	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Cylinder Block

YM***11	Joint,Drain	1
YM***00	Gauge,Oil Level	1
YM***10	Bushing	1
YM***00	Plug	2

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Flywheel And Flywheel Housing

YM***20	Bolt Plated	3
YM***52	Bolt	6
YM***20	Parallel Pin	2
YM***80	Parallel Pin	2

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Front Cover And Gear

YM***22	Retainer, Idle Gear	1
YM***51	Cap, Lub. Oil Supply	1
YM***00	Ring, Snap	1
YM***40	O-Ring,Drain Plug	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Oil Pan

YM***40	Plug,Drain	1
YM***52	Bolt Plated	20
YM***80	Oil Pan Ass'Y	1
YM***80	O-Ring,Engine Oil Drain	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Block : Piston And Connecting Rod

YM***00	Piston Ring Ass'Y	1
YM***10	Bearing (--0.25 mm)	1
YM***30	Piston Ass'Y	3
YM***00	Ring,Snap	6

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Cylinder Head

Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Air Cleaner

YM***50	Case,Air Cleaner	1
YM***10	Cap	1
YM***80	Bolt,Wing	1
YM***90	Washer	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Air Intake Manifold And Connection

YM***10	Gasket, Suction Manifold	1
YM***82	Bolt	1
YM***20	Wire,Glow Plug	1
YM***02	Nut	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Cylinder Head

YM***00	Screw	14
YM***00	Plug	2
YM***10	Valve, Exhaust	3
YM***40	Seat,Intake And Exhaust (Kit)	6

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Cylinder Head Cover

YM***00	Pipe,Breather	1
YM***51	Cap, Lub. Oil Supply	1
YM***10	Gasket,Head Cover (Kit)	1
YM***20	O-Ring,Cylinder Head Cover Bolt	2

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Exhaust Manifold And Muffler

YM***00	Manifold, Exhaust	1
YM***22	Stud	2
YM***30	Muffler	1
YM***02	Stud	2

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Komatsu : 3d68e-3b(S/N 00101-Up) : Cylinder Head : Rocker Arm

YM***30	Screw,Adjusting	2
YM***50	Rocker Arm Ass'Y,Intake	3
YM***02	Nut	2
YM***70	Screw	1

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Electrical System

Komatsu : 3d68e-3b(S/N 00101-Up) : Electrical System : Alternator (20a)

YM***00	Stator Ass'Y	1
YM***10	Bearing,Ball	1
YM***02	Alternator A. (20a)	1
YM***00	Nut,Ball	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Electrical System : Alternator And Mounting (20a)

YM***02	Bolt Plated	1
YM***52	Screw	1
YM***30	Plate,Adjust	1
YM***02	Bolt	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Electrical System : Safety Relay? Current Limiter? Charge Indicator? Grow Relay And Timer

YM***21	Indicator, Charging	1
YM***20	Timer,Solenoid	1
YM***10	Relay,Stop Solenoid	1
YM***11	Limiter, Current	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Electrical System : Starting Motor

YM***01	Washer,Spring	1
YM***20	Cover	1
YM***51	Nut	1
YM***51	Yoke Ass'Y	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Electrical System : Starting Motor And Mounting

YM***52	Bolt Plated	2
(Y***1)	Starting Motor Ass'Y,(See Fig.A6210-B0a1)	1

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Fuel System

Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Fuel Feed Pump And Mounting

YM***21	Feed Pump Ass'Y	1
YM***62	Bolt Plated	2
YM***51	Gasket (Kit)	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Fuel Filter And Piping

YM***20	Fuel Filter Ass'Y	1
YM***40	Lever	1
YM***00	O-Ring (Kit)	1
YM***80	Pipe	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump

Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Fuel Injection Pump And Piping

YM***20	Retainer, Pipe	1
YM***30	Pipe,Injection? No.3	1
YM***50	Shim Ass'Y	1
YM***62	Bolt Plated	3

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Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Fuel Nozzle And Spill Pipe

YM***40	Spacer, Valve Stop	1
YM***00	Fuel Nozzle Ass'Y	3
YM***00	Sleeve	1
YM***80	O-Ring (Kit)	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Governor Control

YM***00	Pin, Cotter	1
YM***00	Retainer, Shaft	1
YM***30	Screw,Adjust	1
YM***14	Pin,Spring	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Fuel System : Water Separator

YM***00	Gasket	2
YM***00	O-Ring (Kit)	1
YM***50	Plug,Air	2
YM***10	Bowl, Fuel Strainer	1

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Lubricating Oil System

Komatsu : 3d68e-3b(S/N 00101-Up) : Lubricating Oil System : Lubricating Oil Filter

YM***50	Nut	1
YM***00	Valve Ass'Y	1
YM***50	Cartridge,Engine Oil	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Lubricating Oil System : Lubricating Oil Pump

YM***50	Oil Pressure Transmitter	1
YM***22	Screw	2
YM***81	Pipe,Inlet	1
YM***20	O-Ring,Cylinder Head Cover Bolt	1

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Tool And Kit

Komatsu : 3d68e-3b(S/N 00101-Up) : Tool And Kit : Gasket Kit

YM***10	Gasket, Suction Manifold	1
YM***10	Gasket Kit	1
YM***10	Gasket,Head Cover (Kit)	1
YM***40	O-Ring,Drain Plug	1

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Komatsu : 3d68e-3b(S/N 00101-Up) : Tool And Kit : Tool

YM***60	Wrench,Fuel Filter? Water Separator	1
YM***50	Screw Driver	1
YM***51	Wrench,(For Engine Oil Filter)	1
YM***10	Flex Horn (Optional)	1

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3D68E-3B(S/N 00101-UP) serial number reference

The 3D68E-3B engine's own ID plate is on the engine block itself, typically near the injection pump or valve cover, and reads as a plain numeric serial block such as 00101 and up rather than a letter-coded PIN prefix. The host PC05-7 mini excavator's own serial/PIN plate is mounted on the machine frame, typically near the operator's seat or at the boom foot pivot, and on these Japan-built minis it is likewise a bare numeric or letter+numeric range (e.g. 8001-UP for general-market build, F20001-UP for the Italy-assembled build) rather than a Cat-style alpha prefix. Identify the machine by matching model, plant block, and serial together in the parts book rather than by a 3-letter code.

Prefix	Identifies	Notes
00101-UP	3D68E-3B engine, own serial block	Engine's own stamped serial range. Naturally aspirated, indirect-injection 3-cylinder diesel, Yanmar-built (3TNE68/3TNE68C equivalent). Fitted as the powerplant for the PC05-7 mini excavator. Distinct from the later 3D68E-3G/3H/3K block, which starts at a separate higher serial break and covers a different mini-excavator lineup, and from the 2D68E-3A twin-cylinder variant used in the PC07-2. Not fitted to the PC12UU-2 mini excavator, which uses an unrelated 3D72-family engine.
8001-UP	PC05-7 host chassis range, general/export build	Chassis/PIN serial break for the general-market PC05-7 fitted with the 3D68E-3B engine. Appears consistently across parts-book sections for this model and serial start. Parts groupings show a running change partway through this block (roughly mid-10,000s), so confirm the exact 3D68E-3B cutoff with your dealer before ordering engine parts late in this range.
F20001-UP	PC05-7 host chassis range, Italy-assembled build	Separate regional production block for a European/Italian-built PC05-7 sharing the 3D68E-3B engine fitment. Numbering differs from the general-market PC05-7 range, so treat as a distinct plant block, not a typo. Confirm engine fitment for this specific serial block with your dealer.

Frequently asked questions

What are the specs of the Komatsu 3D68E-3B(S/N 00101-UP) engine?

It is a naturally aspirated, water-cooled, indirect-injection 3-cylinder diesel displacing about 0.78 liters (68 mm bore x 72 mm stroke). Rated output is 10.3 kW (13.8 hp) at 2400 rpm on the general-use governed setting, with a governed range from about 8.6 kW (11.5 hp) at 2000 rpm up to 12.9 kW (17.3 hp) at 3000 rpm depending on the governor speed setting selected for the application.

What is the operating weight of machines built with the 3D68E-3B?

Its confirmed application, the Komatsu PC05-7 mini excavator, runs roughly 1.2 to 1.4 tonnes (about 2,650-3,090 lb) operating weight, varying by production year and configuration.

What replaced the Komatsu 3D68E-3B?

Not documented as a direct one-for-one replacement on this chassis. The broader 68E-88E engine family continued in later-suffix variants — 3D68E-3G, 3D68E-3H, and 3D68E-3K — fitted to a different Komatsu mini-excavator lineup starting at a later serial break; parts commonality across the family stays high since they share the same 3-cylinder architecture.

What 3D68E-3B(S/N 00101-UP) owners discuss

What host machine actually runs the 3D68E-3B (S/N 00101-UP), and does that matter for troubleshooting?

This engine is the mechanically-injected, naturally aspirated 3-cylinder diesel confirmed as the powerplant for the Komatsu PC05-7 mini excavator at this serial range. It belongs to a wider 68E-88E engine family shared in concept across several small Komatsu excavator badges, but always confirm the engine's own serial block stamped on the block itself rather than assuming fitment from the machine model tag — related blocks such as 3D68E-3G/-3H/-3K power a different mini-excavator lineup starting at a separate, later serial break and are not interchangeable on specs with this -3B, 00101-UP range.

Is a puff of white or light smoke on cold startup something to worry about?

No, not by itself. These are mechanically governed, indirect-injection small diesels without electronic engine management, and a brief smoke puff on a cold start — especially before glow plugs and the block reach temperature — is normal behavior reported across this engine family. What's not normal is smoke that persists past warm-up, or smoke paired with rough idle or a power drop, which points to worn injectors, uneven fuel delivery, or air trapped in the injection lines rather than just cold weather.

The machine won't start or won't move even though the battery and hydraulics seem fine — where do owners look first?

The most commonly reported cause on this class of mini excavator is the safety lever (lockout) switch mounted in the left armrest console. When that switch or its wiring fails, the machine either won't crank or will start but refuse to move any hydraulic function, since the control system reads the lever as still "up." Owners also check the travel motor and final drive for internal blockage if the machine starts and other functions work but travel alone won't respond. Because this switch is a safety interlock, have your dealer verify the fix rather than leaving it permanently bypassed.

What hydraulic behavior is considered normal wear versus a real fault on machines this age?

Some boom or arm settling over several minutes when parked under load is common as seals age, but noticeable drift within a short hold, or one function going sluggish while others stay strong, usually means a worn control-valve spool or cylinder seal rather than a pump problem. Multi-function work (curling the bucket while swinging, for example) getting weak or jerky is a frequently reported early sign of internal leakage. Persistent boom drop under a raised load is a safety issue — have your dealer verify the control valve and cylinder seals before continuing to operate.

What undercarriage and track wear patterns show up on this size of Komatsu mini excavator?

Rubber-track wear concentrates at the drive sprocket lugs and the outer track edges first, and a track that's begun to sag or run loose usually points to a leaking or worn tensioner rather than the track itself. Because the undercarriage and final drives are among the costliest components to repair on a machine this size, owners buying used routinely get down and check track tension, look for uneven wear side-to-side (a sign of misalignment), and listen for grinding or whining from the travel motors and swing gear during a test run.

Are there known electrical or sensor gremlins on this engine and machine generation?

This engine predates onboard fault-code diagnostics, so there's no ECM to throw codes — issues here are almost always simple sender or wiring problems: a corroded coolant-temperature or oil-pressure sender connector giving a false gauge reading, or the safety lever switch mentioned above. Persistent overheating traced back to a failing water pump seal is also a recurring theme in this engine family, and left unaddressed it risks a blown head gasket. Any true overheating event should be checked by a dealer before returning the machine to work.

What should I check before buying a used machine with this engine?

Start the engine cold if possible and watch for hard starting, excess smoke past warm-up, or rough idle. Run every hydraulic function together to load the pump, then hold the boom and arm up to watch for drift. Get down and check track tension and wear pattern on both sides, and rotate the upper structure through a full turn listening for grinding from the swing bearing. Ask for oil-change and filter records, since low-quality fuel and stretched service intervals are the biggest factors that shorten life on this engine family. Have your dealer verify hydraulic pressures and any structural welds before finalizing a purchase.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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