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Yamaha 40VMHD Specifications
| Engine Model: Yamaha 40VMHD |
| Engine Type: 2-stroke inline 3-cylinder gasoline outboard engine |
| Total Displacement: 42.6 cu.in (698 cc) |
| Rated Engine Power: 40 Hp (29.4 kW) at 5000 rpm |
| Fuel System: Carburetor |
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| General Technical Data |
The Yamaha 40VMHD is a 40-horsepower,
three-cylinder, two-stroke outboard engine, part of a series known for
delivering robust and reliable power for a range of boating
applications. This model is engineered for simplicity and durability,
featuring a manual start system and tiller control for straightforward
and responsive operation. Its design prioritizes ease of use and
maintenance, making it a suitable choice for operators who value direct
control over engine functions.
The engine's loop-charged scavenging system and through-propeller
exhaust contribute to efficient power delivery, while the inclusion of a
12-80W alternator provides charging capability for a battery. The Yamaha
40VMHD is constructed to withstand demanding marine environments,
offering a dependable power source for various watercraft.
The Yamaha 40VMHD is a 2-stroke, inline 3-cylinder engine (L-type). The
total displacement is 698 cc (42.6 cu.in), achieved through a bore and
stroke of 67.0 mm (2.64 inches) and 66.0 mm (2.60 inches), respectively.
It produces a maximum prop shaft output of 29.4 kW, equivalent to 40
horsepower, at 5,000 rpm.
The engine has a full throttle operating range of 4,500 to 5,500 rpm.
The compression ratio is stated as 6.0:1. The idle speed should be
inspected and adjusted with the motor in the water or a test tank, using
a tachometer for accurate measurement.
| Powerhead |
The engine utilizes a loop charge scavenging system, which optimizes the fuel-air mixture delivery and exhaust removal for efficient combustion. The intake system employs reed valves.
The powerhead is designed for longevity and dependable operation in various conditions. The starting serial number block for the worldwide 40VMHD long shaft model begins at L: 560290, and the approved model code for this configuration is 6H4.
| Fuel System |
The fuel system is based on three individual carburetors, one for each cylinder. Starting enrichment is controlled by a manual choke valve. The engine operates on regular unleaded gasoline with a minimum octane rating of 86.
The fuel system includes a filter that should be checked periodically for water or foreign matter, with cleaning or replacement performed by an authorized dealer if necessary.
| Lubrication System |
The lubrication system is a pre-mix type, where the engine oil is mixed directly with the fuel. The recommended fuel-oil mixing ratio is 50:1.
The specified engine oil is a 2-stroke outboard motor oil that meets NMMA-certified TC-W3 grade standards. Yamaha recommends using YAMALUBE 2-stroke outboard motor oil for optimal performance and protection.
| Cooling System |
Cooling is managed by a raw-water system that circulates water through the engine block and cylinder head to maintain optimal operating temperatures. The system is designed to provide consistent cooling across the engine's operating range, ensuring reliability and preventing overheating during extended use.
| Mid Section and Lower Unit |
The exhaust system is designed to expel gases through the propeller
boss, contributing to quieter operation and reduced underwater noise.
The gear shift positions are forward, neutral, and reverse. The gear
ratio is 1.85 (derived from a 24/13 gear set). The reduction gear type
is spiral bevel gear, and the clutch is a dog type.
The propeller shaft utilizes a spline drive, and the propeller rotation,
when viewed from the rear, is clockwise. The gear case requires hypoid
gear oil meeting API GL-4 SAE 90 standards, with a total capacity of
0.43 liters (0.45 US quarts). The lower unit is designed for durability
and requires specific tools for service procedures such as bearing and
seal replacement.
| Trim and Tilt System |
The engine is equipped with a manual tilt system. The tilt-up angle is 69 degrees. The trim angle is adjustable within a range of -4 to 20 degrees, allowing operators to optimize boat attitude and performance for varying load and water conditions. The steering angle is 40 degrees in both directions, providing responsive maneuverability with the tiller handle.
| Propeller Information |
A wide range of propeller sizes is available for the Yamaha 40VMHD to
accommodate various boat types, loading conditions, and performance
requirements. All propellers have three blades and utilize a spline
drive system.
Available sizes, listed by diameter and pitch in inches, include: 10 x
15, 10-1/4 x 14, 10-3/4 x 16, 10-3/4 x 17, 10-3/8 x 13, 10-5/8 x 12,
11-1/8 x 13, 11-1/4 x 14, 11-3/8 x 12, 11-5/8 x 11, 11-3/4 x 10, 12-1/4
x 9, 12 x 11, and 12 x 12. Selecting the correct propeller is essential
for achieving optimal engine performance within the recommended full
throttle operating range.
| Dimensions and Weight |
The overall length of the outboard is 1,281 mm (50.4 inches), and its overall width is 349 mm (13.7 inches). The overall height for the long shaft model is 1,350 mm (53.1 inches), designed for a transom height of 508 mm (20.0 inches).
The dry weight for the long shaft version is 84 kg (185.2 lbs). These dimensions and weight make it a manageable yet powerful outboard for a variety of boats requiring a 20-inch transom.
| Maintenance Data |
Routine maintenance is essential for optimal performance and longevity.
The engine is equipped with a CDI (Capacitor Discharge Ignition)
ignition system with electric automatic advance. The alternator output
is 80W at 12V, providing charging capability. The standard spark plug
for the 40VMHD model is an NGK BR7HS-10. The spark plug gap should be
maintained between 0.9 and 1.0 mm (0.035 to 0.039 inches).
When installing spark plugs, the threads should be clean, and the plug
should be torqued to specification. If a torque wrench is not
immediately available, the plug can be initially tightened 1/4 to 1/2
turn past finger-tight, with final torquing performed as soon as
possible.
Periodic inspection and cleaning of the fuel filter are recommended to
ensure no water or foreign matter has accumulated. Service procedures
such as lower unit maintenance require specialized tools for tasks like
backlash measurement and shimming, including a tachometer, dynamic spark
tester, dial indicator, and various pullers and installers for bearing
and seal work.
| Tightening Torques |
Adhering to correct torque specifications is critical during assembly
and maintenance to ensure proper sealing, component retention, and safe
operation. Critical fasteners require precise torquing, often in
specific sequences or stages. The cylinder head bolts are tightened in a
two-step process: first to 15 Nm (11 lb-ft), and finally to 28 Nm (20
lb-ft).
The engine unit bolt requires 21 Nm (15 lb-ft). The flywheel nut is a
critical fastener torqued to 110 Nm (80 lb-ft). The reed valve bolt is
set to a light 1 Nm (0.7 lb-ft). The spark plug is torqued to 25 Nm (18
lb-ft). The propeller nut is set at 30 Nm (22 lb-ft). The lower unit
bolt requires 40 Nm (29 lb-ft).
The propeller shaft housing bolt is torqued to 16 Nm (11 lb-ft). Tiller
handle components have specific torques: the mounting nut is 38 Nm (27
lb-ft), the steering friction mounting nut is 20 Nm (14 lb-ft), and the
tiller handle pivot bolt is 38 Nm (27 lb-ft). Both the muffler bolt and
exhaust manifold bolt are torqued to 21 Nm (15 lb-ft), and the exhaust
guide bolt also requires 21 Nm (15 lb-ft).
| Boat Applications |
The Yamaha 40VMHD is intended for use on boats where the total
horsepower does not exceed the vessel's maximum rated power capacity, as
indicated on the boat's capacity plate. Its 40-horsepower output, tiller
control, and manual start make it suitable for a wide range of small to
medium craft, including aluminum fishing boats, jon boats, utility
skiffs, and workboats where simplicity, durability, and ease of
maintenance are prioritized.
The long shaft configuration is designed for boats with a 20-inch
transom. Proper installation and adherence to the boat's maximum
horsepower rating are essential to ensure safe handling and prevent loss
of control.
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