Tag: Engine Mounts

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How to install an inboard engine?

Are you planning to install or modify an inboard engine yourself? Prepare well, start with the basics, and take measurements. With minimal adjustments, you can replace an engine. For recent engines, you often know the installation dimensions or they are easy to find. Pay special attention to:

Make sure to figure out what you need.

Are you still looking for a used engine? Quickly check out our range of used marine engines.

Propeller shaft height

First, check if the engine fits in combination with the propeller shaft height. Is the output of the reverse coupling at the same height as the crankshaft? If the output of the reverse coupling is lower than the existing propeller shaft, the engine will need to be raised.

Engine mounts

On some inboard engines, adjusting the existing engine mounting points is no problem, or the foundation of the steel hull can be modified. In a polyester boat, this becomes more difficult. Therefore, check beforehand if this is possible. Especially with a saildrive, you’re often bound to existing prefab transom fittings.

Maximum tilt

Also check if the inboard engine can handle the maximum tilt while sailing. The maximum tilt is often listed in the manual. A homokinetic drive solves the problem otherwise.


Reverse coupling

The Velvet, PRM reverse coupling, Hurth, ZF, and Twindisc reverse couplings are common reversing couplings. The ratio is often indicated by the engine RPM divided by the output RPM, in a two-to-one (2:1) ratio. Ratio = Two engine revolutions / one propeller shaft revolution (or simply half).

The rotation direction of the output is often indicated as L or R in the 2:1 ratio. L is a two-to-one left-turning reverse coupling for a left-handed propeller.

You may also encounter reverse couplings with an A for angle, for example, in Volvo Penta. These reverse couplings come with a shaft tilted 7 degrees outward. This way, the engine needs to tilt less.

Propeller

Pay attention to the rotation direction of the propeller. There are left-handed and right-handed reverse couplings. The rotation direction of the reverse coupling is indicated when the boat is moving forward and you are looking at the bow.

Be careful with a “Z-drive.” The engine is then reversed, so make sure to check the specifications carefully.

AB Marine Service can perform the power requirement calculation for your boat.

Power

If the power remains in the same direction, you can often reuse the same inlet and outlet connections, such as the exhaust gas outlet, cold water supply, or circulation pipes.

If you are increasing or decreasing the power, check the diameter of the connection on the engine. This is already a good indicator of the required size.

If the exhaust manifold is 45.00 mm, you can use this diameter. Do not go smaller, as it will restrict the engine, leading to potential issues. Going larger is usually not a problem.

Propeller shaft and bearing

Also think about connecting the propeller to the reverse coupling. Some brands are interchangeable, but this is not always the case. You will need an adapter flange. These can be obtained separately upon request or are often supplied ready-made with a homokinetic drive.

If you want to reduce vibration and save time with the connection, consider the advantage of a thrust bearing with a homokinetic drive.

What do you need?

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A flexible engine mount, constant velocity joint?

How can my boat be quieter and my sailing more relaxed?

Have you ever enjoyed a nice boat trip but then had to turn the throttle back because of the noise? For relaxation, you want to be able to hear each other, right? Consider a flexible engine mount.

A flexible engine mount

With a flexible engine mount, you use engine supports. These supports reduce noise and vibrations as much as possible.

Sailing without vibration

What is the key to sailing without (too much) vibration and having a relaxing sail? The principle is simple. You remove the rigid connection between the engine and the foundation. This transmits the vibrations from the engine. Let the engine float on its foundation, and the noise is gone. Start with the basics.

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Why do engines vibrate?

Engines have internal components that move quickly back and forth. In milliseconds, the piston is forced down by an explosion and then pushed back up by the crankshaft at the same speed for a new compression stroke. With short piston strokes and aluminum engine blocks, modern engines are made compact and lightweight. This provides many advantages, such as space savings and lower production costs. A disadvantage is that vibrations are less dampened and absorbed due to the low weight. Also, the shorter engine stroke requires higher RPMs to stay running. As you know from experience, the more throttle you give, the more noise you get.

Loose support of the engine

That’s why it is important to ensure a good and solid foundation for the engine with soft engine supports. The supports essentially decouple the engine from the boat’s foundation. The best option is a soft enough engine support that is still strong enough to support the weight of the engine, reverse gear, and part of the propeller shaft.

As soft as possible rubber

The softness of rubber is expressed in SHORE with a number for hardness. Additionally, the letter A to D determines in which category the rubber belongs. Rubber with a SHORE of 10 is very soft, and above that, it becomes firmer. A heavier engine requires firmer rubber to ensure that the rubber isn’t pressed out by the weight. Engine supports usually start at 35 SHORE. Look for rubber that is soft enough, but still firm enough to support the engine. The softness and quality of the rubber often determine the final price and durability.

Don’t skimp on the price of good engine supports. Cheaper engine supports, like washing machine mounts, sometimes work well but aren’t always resistant to oil, grease, and diesel fumes in the engine compartment.

Too soft?

With too soft engine supports, the strength is lost in the pull and thrust motion made by the propeller shaft and engine during maneuvering. You can choose V-engine supports, which lock the engine in place under load with their V-shape. However, this does reduce damping because the engine pushes against the rubber.

dempersSo what is the optimal engine mount?

Do you want optimal damping? A combination of flat vibration dampers with a thrust/bearing is the best solution. A thrust/bearing keeps the propeller shaft in place. It is a bearing that absorbs forces from all directions. This is also suspended in rubbers and mounted between the reverse gear and the propeller shaft. After installation, it must be precisely aligned to prevent overload of the bearings and shaft seals. Even better is placing a flexible (homokinetic) coupling between the coupling and shaft, allowing all parts to continue rotating without stress, even under load and possible shifting.

Example setup of a homokinetic engine mount

Advice for less vibration while sailing

Looking for less vibration and more relaxation? Or a better engine setup? Take a close look at the foundation of the engine setup. Can this be improved? Feel free to consult with our specialists. Each engine and coupling brand requires its own force calculations. Based on this data, we can develop a plan for you.
As preparation, we’d like the following details:

– Brand and type
– Maximum RPM
– Number of cylinders
– Engine weight
– Thrust bearing installed

AB Marine Service provides setups for any brand, type of engine, and reverse gear. Request your own relaxing sail today.