Yanmar 4LHA HTP Specifications
| Engine Model: Yanmar 4LHA HTP |
| Engine Type: 4-stroke inline 4-cylinder turbocharged water-cooled diesel |
| Total Displacement: 211 cu.in (3.45 L) |
| Rated Engine Power: 160 Hp (118 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 4LHA-HTP is a 4-stroke, vertical,
water-cooled marine diesel engine from the LHA series. Designed as a
compact, high-power-to-weight solution for powerboats, this engine is
suited for planing hulls, semi-displacement cruisers, and light
commercial vessels. The HTP designation indicates a high-output
configuration with turbocharging and intercooling. Produced from the
late 1990s through the mid-2010s, the 4LHA-HTP represented Yanmar’s
approach to powering smaller planing craft with diesel efficiency and
durability.
The engine’s 3.5-liter displacement produces 160 hp at 3,300 rpm,
achieving a power-to-weight ratio advantageous for vessels requiring
speed without the fuel consumption of gasoline engines. The 4LHA-HTP
incorporates direct injection, a VE rotary injection pump, and a
fresh-water cooling system with heat exchanger, engineered for sustained
high-speed marine operation.
The Yanmar 4LHA-HTP engine is recognized for its high power density,
compact dimensions, and reliable starting characteristics. The
turbocharged and intercooled configuration provides strong mid-range
torque, allowing planing hulls to achieve plane quickly and maintain
speed without excessive fuel consumption. The direct injection
combustion system delivers improved fuel efficiency compared to indirect
injection designs, a significant advantage for vessels covering long
distances. The fresh-water cooling system with heat exchanger isolates
the engine block from seawater corrosion, extending service life in
saltwater environments.
The engine's dry weight of 342 kg (754 lb) without marine gear supports
favorable vessel weight distribution. The availability of multiple
transmission options including the KMH50A hydraulic gear, KMH50V
V-drive, and ZF63A accommodates diverse vessel configurations and
sterndrive applications. Service considerations include regular valve
clearance checks and attention to the turbocharger and intercooler
system for sustained high-output operation.
Engine Type: Vertical inline 4-cylinder, 4-cycle, water-cooled
turbocharged diesel.
Family: Yanmar LHA series.
Displacement: 3.455 liters (211 cu.in), equivalent to 3.5 L.
Bore: 100.0 mm (3.94 in).
Stroke: 110.0 mm (4.33 in).
Compression Ratio: 17.8:1.
Combustion System: Direct injection.
Aspiration: Turbocharged with intercooler (air-to-air or air-to-water).
Valvetrain: OHV (Overhead Valve), 2 valves per cylinder (8 total).
Firing Order: 1-3-4-2.
Rotation (from flywheel end/stern): Counter-clockwise.
Rated Speed Range: 3,000-3,300 rpm.
Maximum Output (Crankshaft): 118 kW (160 hp) @ 3,300 rpm.
Continuous Rating Output (Marine propulsion): 91 kW (124 hp) @ 3,100
rpm.
Maximum Torque: 380 Nm (280 lb-ft) @ 2,200-2,600 rpm.
Cruising RPM Range: 2,800-3,200 rpm.
Low Idle Speed: 700-750 rpm.
The cylinder block is constructed from cast iron with a closed-deck
design. The block features integral cylinder bores machined directly
into the casting, surface-hardened with a honed finish for piston ring
compatibility. The four-cylinder block incorporates five main bearing
webs supporting a forged steel crankshaft with five main bearings. The
crankshaft is induction-hardened at the journal surfaces and features
eight counterweights for vibration control.
The block features a deep-skirt configuration extending below the
crankshaft centerline, with reinforced bulkheads at each main bearing
location. Integrated oil galleries within the block supply the
crankshaft main bearings, connecting rod bearings, and camshaft
bearings. Piston cooling oil jets are mounted in the block, directing
continuous oil streams to the underside of each piston crown for thermal
management under sustained high-power operation. The timing gear housing
is integrated into the front of the block.
The cylinder head is manufactured from cast iron and houses the overhead
valve (OHV) arrangement with two valves per cylinder. The cross-flow
design positions intake ports on one side and exhaust ports on the
opposite side, improving volumetric efficiency and cooling of the
exhaust valve area. Intake valves measure 38.0 mm (1.50 in) in diameter,
while exhaust valves measure 34.0 mm (1.34 in). The valvetrain consists
of a single camshaft located in the cylinder block, operating the valves
through hardened pushrods and forged steel rocker arms.
Valve seat inserts are replaceable and manufactured from sintered alloy
material for wear resistance under high exhaust temperatures. Valve
clearance is adjusted by a screw and locknut on each rocker arm. The
cylinder head is secured by four head bolts per cylinder (16 total),
requiring a multi-step torque sequence. The direct injection combustion
chambers are recessed bowls in the piston crowns, with the injector
nozzles mounted centrally in the cylinder head.
The fuel system employs a mechanical direct injection architecture using
a Bosch VE-type rotary distributor injection pump. The VE pump is
flange-mounted to the timing gear housing and driven by the engine's
gear train. A mechanical governor, integrated into the injection pump,
maintains engine speed under varying loads through a centrifugal weight
mechanism. An aneroid compensator (boost compensator) adjusts fuel
delivery under turbocharger boost conditions, optimizing the air-fuel
ratio across the engine speed range.
High-pressure injection lines deliver fuel to multi-hole injectors
mounted in each cylinder head. Injector opening pressure is factory set
between 200 and 220 bar (2,900-3,190 psi). A mechanical fuel feed pump,
mounted on the injection pump, draws fuel from the tank and supplies it
through a spin-on primary fuel filter and a secondary fuel filter. A
manual primer lever on the feed pump allows bleeding air from the system
after filter changes.
The lubrication system is a forced-feed, wet-sump type utilizing a
trochoid-type oil pump mounted to the front timing gear housing. The
trochoid pump design provides smooth, pulseless oil flow with reduced
noise compared to gear pumps. The pump is driven by the camshaft gear,
ensuring immediate oil pressure upon startup. Oil is drawn from a cast
aluminum oil pan through a strainer before pressurization. A full-flow
spin-on oil filter is mounted externally on the cylinder block.
The system supplies lubricant to the crankshaft main bearings,
connecting rod bearings, camshaft bearings, timing gears, pushrods,
rocker shaft, valve tips, and turbocharger center bearing. The oil pump
incorporates a pressure relief valve set between 3.5 and 4.5 bar (50-65
psi) at rated speed. A seawater-cooled oil cooler is integrated into the
lubrication system to maintain oil temperature under sustained
high-power operation. The oil pan capacity accommodates extended
operation with a dipstick on the side of the block indicating oil level.
The cooling system is a freshwater (closed-circuit) cooled system with a
heat exchanger, isolating the engine block from seawater corrosion. A
centrifugal fresh-water pump, gear-driven from the timing gear housing,
circulates coolant through the cast-iron cylinder block and cast-iron
cylinder head. A wax-type thermostat with a rated opening temperature of
82°C (180°F) regulates the engine operating temperature. The heat
exchanger is a tube-in-shell design mounted on the engine.
A rubber-impeller seawater pump, belt-driven from the crankshaft pulley,
draws seawater through a seacock and strainer, passes it through the
heat exchanger and oil cooler, and discharges it overboard. The
intercooler (charge air cooler) is integrated into the intake manifold
and may be seawater-cooled or fresh-water-cooled depending on
configuration. The freshwater capacity is 8.0 liters (8.5 qt) inclusive
of the engine block and heat exchanger.
| Intake and Exhaust Systems |
Intake System: Air is drawn through a dry-type paper element air filter
or flame arrestor before entering the turbocharger compressor inlet.
After compression and intercooling, air enters the intake manifold. The
intake manifold is cast from aluminum and incorporates the intercooler
within the manifold body.
Exhaust System: A cast-iron exhaust manifold collects gases and directs
them to the turbocharger turbine inlet. After the turbocharger, exhaust
gases pass through a water-injected exhaust elbow. Seawater is injected
into the exhaust elbow to cool exhaust gases before they pass through
the exhaust hose and waterlock/silencer system.
Timing System: The camshaft is driven by a gear train from the
crankshaft. Hardened steel timing gears at the front of the engine
provide fixed timing without belts or chains requiring replacement. The
gear train sequentially drives the crankshaft gear, idler gear, camshaft
gear, and injection pump gear. Timing marks on each gear must align
during assembly. No timing tensioner is present due to the fixed gear
arrangement.
Turbocharging System: A fixed-geometry turbocharger (Mitsubishi TD
series or IHI) is flange-mounted to the exhaust manifold. The
turbocharger utilizes exhaust gas energy to compress intake air,
increasing volumetric efficiency and power output. An intercooler
(charge air cooler) reduces compressed air temperature before entry to
the intake manifold, increasing air density and combustion efficiency.
The turbocharger bearing housing is supplied with engine oil through a
dedicated feed line and returns oil to the crankcase.
Starting System: A 12-volt electric starter motor (2.5 kW) is mounted to
the flywheel housing, engaging a ring gear on the flywheel. A 12V/80A
alternator maintains battery charge and supplies electrical power for
navigation equipment, lighting, and vessel systems. The electrical
system is designed for marine environments with corrosion-resistant
terminals and sealed connectors.
Glow Plug System: Individual pencil-type glow plugs are mounted in each
cylinder head. Glow plug operation is controlled by a timer relay, with
pre-heat times of 5-10 seconds depending on ambient temperature. A glow
indicator lamp on the helm signals when starting can commence.
Overall Engine Length (without gearbox): 1,100 mm (43.3 in) from front
cover to flywheel housing.
Overall Engine Length (with KMH50A gear): 1,131 mm (44.5 in).
Overall Engine Width: 719 mm (28.3 in).
Overall Engine Height (without gearbox): 811 mm (31.9 in) from oil pan
bottom to rocker cover top.
Dry Weight (Bobtail, without gearbox): 342 kg (754 lb).
Dry Weight (with KMH50A hydraulic gear): 380 kg (838 lb).
Dry Weight (with KMH50V V-drive): 400 kg (882 lb).
Engine Oil Capacity (with Filter): 8.5 liters (9.0 U.S. qt, 7.5 imperial
qt).
Engine Oil Specification: API CD, CE, CF, CF-4, or CI-4 grade; SAE
15W-40 or 10W-30.
Coolant Capacity (Freshwater): 8.0 l (8.5 qt) inclusive of the engine
block and heat exchanger.
Coolant Specification: Ethylene glycol-based antifreeze with corrosion
inhibitors.
Seawater Pump Impeller Inspection Interval: 200 operating hours or
annually.
Seawater Pump Impeller Replacement Interval: 500 operating hours or 2
years.
Heat Exchanger Service: 250 hours or annually in saltwater.
Thermostat Opening Temperature: 82°C (180°F).
Fuel Filter Replacement Interval: 250 operating hours or annually.
Primary Fuel Filter Element Replacement: 250 hours.
Oil Change Interval: 250 hours or annually under normal conditions.
Oil Change Interval: 150 hours under severe service.
Valve Clearance (Cold): Intake: 0.20 mm (0.008 in); Exhaust: 0.25 mm
(0.010 in).
Valve Clearance Inspection Interval: 400 operating hours or annually.
Injector Inspection Interval: 800 operating hours for opening pressure
testing.
Injection Pump Timing: Static timing set at 10-12 deg btdc.
Fuel Injection Pressure: 200-220 bar (2,900-3,190 psi, 200-220 kgf/cm2).
Turbocharger Inspection: 1,000 operating hours.
Glow Plug Resistance: 0.5-1.0 ohm at 20°C (68°F).
Engine Mounts: Inspection and alignment annually to prevent shaft and
coupling wear.
Cylinder Head Bolts, Step 1: 30 Nm (3.1 kgf-m, 22 lb-ft).
Cylinder Head Bolts, Step 2: 60 Nm (6.1 kgf-m, 44 lb-ft).
Cylinder Head Bolts, Step 3: 90 Nm (9.2 kgf-m, 66 lb-ft).
Cylinder Head Bolts, Step 4: 120 Nm (12.2 kgf-m, 89 lb-ft).
Main Bearing Cap Bolts: 80 Nm (8.2 kgf-m, 59 lb-ft).
Connecting Rod Cap Bolts: 60 Nm (6.1 kgf-m, 44 lb-ft).
Flywheel Bolts: 70 Nm (7.1 kgf-m, 52 lb-ft).
Crankshaft Pulley Bolt: 180 Nm (18.4 kgf-m, 133 lb-ft).
Camshaft Bearing Cap Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Rocker Arm Shaft Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Intake Manifold Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Exhaust Manifold Nuts: 30 Nm (3.1 kgf-m, 22 lb-ft).
Injection Pump Mounting Nuts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Injector Hold-Down Clamp Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
Turbocharger Mounting Nuts: 40 Nm (4.1 kgf-m, 30 lb-ft).
Oil Filter (Spin-on Type): 18 Nm (1.8 kgf-m, 13 lb-ft).
Oil Pan Bolts: 15 Nm (1.5 kgf-m, 11 lb-ft).
Glow Plugs: 12 Nm (1.2 kgf-m, 9 lb-ft).
Starter Motor Mounting Bolts: 40 Nm (4.1 kgf-m, 30 lb-ft).
Alternator Mounting Bolts: 30 Nm (3.1 kgf-m, 22 lb-ft).
Freshwater Pump Mounting Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Seawater Pump Mounting Bolts: 20 Nm (2.0 kgf-m, 15 lb-ft).
Intercooler Mounting Bolts: 25 Nm (2.5 kgf-m, 18 lb-ft).
The Yanmar 4LHA-HTP engine is utilized exclusively in marine propulsion
applications for powerboats, planing hulls, and light commercial
vessels.
Recreational Powerboats (Plan Hulls)
Express cruisers: 25-32 ft (7.6-9.8 m) planing hulls with single or twin
installations.
Downeast-style powerboats: 28-36 ft semi-displacement cruisers.
Walkaround center console boats: 27-31 ft fishing boats with single
diesel power.
Cuddy cabins and sport cruisers: 26-30 ft vessels requiring planing
capability.
Fishing Vessels
Sportfishermen: 28-34 ft convertible sportfishing yachts.
Inshore fishing boats: Commercial and charter vessels for day trips.
Lobster boats: Downeast-style hulls converted for recreational use.
Light Commercial Marine
Patrol boats: Law enforcement and security vessels requiring sustained
high-speed operation.
Pilot boats: Harbour pilot transfer vessels.
Small passenger vessels: Charter craft and excursion boats.
Workboats: Harbour utility vessels and small tug applications.
Sterndrive Applications (4LHA-HTZP)
Volvo Penta sterndrive (DPS, DPH): I/O applications with
through-propeller exhaust.
Mercruiser Bravo sterndrive (Bravo I, II, III): Inboard/outboard
configurations.
Transmission Configurations
KMH50A: Hydraulic multi-disc clutch with 8° down angle for shaft drive.
KMH50V: V-drive configuration with 8° down angle for aft-mounted engine
installations.
ZF63A: Hydraulic wet multi-disc clutch with 8° down angle (ZF Marine
transmission).
Direct drive: Shaft drive through a stuffing box and cutlass bearing.
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