This is a general, instructive guide to how the system works and what to look for. It is not a service manual, and it is not specific to your truck. Procedures, clearances, pressures, torque figures and service limits differ between makes, models and build dates, and the manual for the machine you are actually working on is the only authority on what is correct for it. Work to that manual, and to your employer's safety procedures.
The two engines
The 4G63 and 4G64 are two members of Mitsubishi's 4G6 engine family, and between them they power a large share of the gas and LPG lift trucks in service. They were supplied to multiple manufacturers, so the same engine turns up under several brands and several part numbering systems. They are closely related, and the parts that do not interchange are exactly the ones people assume will.
| 4G63 | 4G64 | |
|---|---|---|
| Displacement | 1,997 cc, about 2.0 liters | 2,351 cc, about 2.4 liters |
| Bore | 85.0 mm | 86.5 mm |
| Stroke | 88.0 mm | 100.0 mm |
| Typical industrial output | 50 to 60 hp | 60 to 75 hp |
Both are cast iron blocks with aluminum cylinder heads, single overhead camshaft driven by a toothed timing belt, naturally aspirated with two valves per cylinder in industrial form. Output moves with fuel type, governor setting and application.
The extra displacement in the 4G64 comes from a modest bore increase and a much longer stroke, which makes it a physically taller engine. It is the more common of the two at the heavier end of the lift truck market, for the obvious reason: more torque at low speed is what a truck actually needs.
What interchanges and what does not
A good number of external and accessory parts cross over: water pump, oil pump, distributor and ignition components, starter, alternator, and much of the fuel system depending on configuration.
What does not cross over is everything determined by displacement. Block, crankshaft, connecting rods, pistons and head gasket are all specific to each engine. The 12 mm stroke difference also means a different deck height, so anything sized to the crank-to-cam distance — the timing belt among it — should be ordered against the specific engine rather than the family.
Cylinder heads are similar between the two and are sometimes described as interchangeable. Treat that as a case-by-case question rather than a rule. Head casting and combustion chamber details varied across the production run, and the head is not a part worth guessing at.
The automotive trap
The 4G63 has an enormous performance aftermarket, because the designation is shared with a turbocharged twin-cam automotive engine used in fast road cars. Searching the engine designation returns a flood of turbo parts, forged internals and performance components, almost none of which fit an industrial engine.
The automotive variant is a substantially different engine: different head, different valvetrain, different fuel system, different accessory drive, and none of the governor and industrial-duty hardware. A part listed as fitting a 4G63 in an automotive context very often will not fit an industrial 4G63, and the price difference will make it look like a bargain right up until it arrives.
Buy against the industrial application and the engine's stamped number, not against the family designation.
Fuel configurations
The engine designation says nothing about the fuel system. These engines shipped in several configurations, and nothing crosses over between them:
- LPG, with a mixer on the intake and a vaporizer or regulator plumbed into the coolant lines
- Gasoline, with a carburetor on earlier units
- Dual fuel, both of the above with a selector
- Electronically controlled on later emissions-compliant units, with a throttle body, sensors and an engine control unit in place of the mechanical mixer
Confirm the fuel system independently of the engine model, every time, before quoting anything from the intake forward.
What fails
- Timing belt and tensioner. These are belt-driven engines, so the belt is a scheduled replacement item, and it is the failure that strands the most trucks. Used equipment is the usual problem: a truck changes hands and the interval never gets picked up.
- Balance shaft components. Some versions carry twin counter-rotating balance shafts driven by their own belt. Where fitted, that belt is a known weak point, and if it fails the debris can take the timing belt with it. Check whether the unit in front of you has them before planning a belt service.
- Valve seat recession on LPG. Propane burns hot and provides no upper-cylinder lubrication, and these engines have aluminum heads. Seat recession is the classic LPG fleet failure, and hardened seats on rebuild are effectively mandatory for propane duty.
- Head gasket and warped head. An aluminum head on an iron block means overheating does real damage. Often secondary to a failing water pump or a plugged radiator.
- Water pump. Belt-driven, so a seized pump can destroy the timing belt as it goes.
- Oil leaks. Valve cover gasket, front crank seal and cam seal are all routine. A wet timing cover is worth investigating rather than topping off, since oil on a timing belt shortens its life considerably.
- Fuel system. LPG regulator and vaporizer diaphragms, mixer wear, and on electronically controlled units the sensors and throttle body.
Confirm whether the specific engine variant is an interference design. The answer differs across the 4G6 family, and it decides whether a broken belt means a belt job or a cylinder head.
Where these engines show up
Supplied as OEM powerplants to multiple lift truck manufacturers, most prominently Mitsubishi Forklift, Caterpillar lift trucks, Clark, Doosan and Daewoo. They also appear outside material handling in industrial sweepers and scrubbers, aerial work platforms, and stationary and portable power equipment.
Identifying which engine you have
Step 1: rule out the diesel
Mitsubishi also supplied diesel engines to the same manufacturers. If the truck is a diesel, neither the 4G63 nor the 4G64 is the answer. These are spark-ignition engines: look for a distributor or coil pack, and either a carburetor, an LPG mixer or a throttle body.
Step 2: read the engine number off the block
This is the authoritative source and the only reliable way to separate a 4G63 from a 4G64.
- Where to look
- A machined flat pad on the block. Position varies across the production run, so check the sides of the block near the bellhousing flange and toward the front of the engine.
- Getting it readable
- The stamps are shallow and usually buried under paint and grease. Degrease, brush the pad clean, then shine a flashlight across it at a low angle. Raking light makes shallow characters legible when direct light will not.
- What to record
- The complete string exactly as stamped, including every dash and suffix character. Suffixes distinguish variants within the same displacement.
On visual comparison: the 4G64's longer stroke makes it a taller engine, so with both side by side the deck height difference is apparent. On its own in a truck, that difference is not something to bet a parts order on. Read the stamp.
Step 3: cross-reference the truck data plate
The nameplate is on the dash cowl, or on a leg of the overhead guard. Record the truck model code and serial number in full. Model and serial cross-reference in the parts manual to the engine the truck left the factory with, and when the block stamp is unreadable this is the best substitute.
Remember that the data plate identifies the machine manufacturer, not the engine manufacturer. A Caterpillar, Clark or Doosan plate is entirely consistent with a Mitsubishi engine underneath. And where the plate and the block stamp disagree, the block stamp wins.
Frequently asked questions
Will 4G63 parts fit a 4G64?
Some will. Accessories and external components largely cross over — water pump, oil pump, ignition, starter, alternator. Anything set by displacement does not: block, crankshaft, rods, pistons and head gasket are specific to each engine, and the 12 mm stroke difference changes the deck height, so the timing belt goes with the specific engine too.
I found cheap 4G63 parts online. Why will they not fit?
Because they are almost certainly for the automotive engine that shares the designation — a turbocharged twin-cam unit used in fast road cars. It has a different head, valvetrain, fuel system and accessory drive, and none of the industrial governor hardware. The designation matches; the engine does not.
Can I tell the two apart by looking?
Side by side, yes: the longer stroke makes the 4G64 a taller engine and the deck height difference shows. On its own in a truck, no. That is not a difference worth betting a parts order on, so read the stamped number.
Does this engine have balance shafts?
Some versions do — twin counter-rotating shafts driven by their own belt. Check before planning a belt service, because where they are fitted that second belt is a known weak point and its debris can take the timing belt with it.
If the timing belt breaks, is the engine damaged?
It depends on whether your specific variant is an interference design, and the answer is not the same across the family. Confirm it before you plan the repair, because it is the difference between a belt job and a cylinder head.
Why do propane trucks need hardened valve seats?
Propane burns hot and provides none of the upper-cylinder lubrication that gasoline does, and these engines have aluminum heads. Seat recession is the classic LPG fleet failure, so hardened seats on rebuild are effectively mandatory for propane duty.
The data plate says Clark. Can it still be a Mitsubishi engine?
Yes. These engines were supplied to several manufacturers, and the plate identifies who built the truck rather than who built the engine. Where the plate and the block stamp disagree about the engine, the block stamp wins.
Before you order
- Read the block stamp first, complete with its suffix. It is the only reliable way to separate the two engines.
- Identify the fuel system separately before quoting anything from the intake forward.
- Ignore automotive listings entirely. The shared designation is a trap, not a cross-reference.
- Order the timing belt against the specific engine, not the family — the deck heights differ.
- Establish whether balance shafts are fitted before quoting a belt service.
- Treat the cylinder head as engine-specific unless you have verified otherwise for your particular pair of castings.
- Specify hardened seats on any head work destined for propane duty.
Not sure which engine you are working with? Send us the engine number stamp and the truck data plate information and we will verify fitment before you order.
This article covers the identification and common failure points of these engines in industrial service. Specifications, service intervals and part numbers vary between build dates, fuel configurations and the manufacturer that fitted the engine. As above, work to the service data for your own machine, and confirm fitment against the stamped engine number rather than the family designation.