Workshop: Replacing engine mounts yourself

At first glance, the engine mounts look inconspicuous, but there are much more exciting components in the engine compartment. The metal and rubber feet support the engine - that's it. But the requirements are complex and sometimes contradict each other. Engine mounts have to fulfil three main tasks simultaneously. Firstly, to hold the machine securely. That sounds banal, but given the forces on board, it is no small matter. Depending on the type, the engine weighs between 80 and several hundred kilograms. In rough seas, additional acceleration forces act on the bearings. The mounting must therefore be absolutely reliable.

Secondly, the bearings must transmit the propulsion force. When travelling under engine power, the entire boat is pushed by the propeller. This force runs via the shaft, the gearbox, the engine and finally via the engine bearings into the hull. When travelling forwards, the propeller pushes; when travelling backwards, it pulls. The engine mounts must absorb these forces in both directions and transfer them to the foundation. If the bearings were to give way too softly, energy would be lost - the boat would accelerate more slowly and the engine would have to work harder. Any yielding means a loss of energy, which is reflected in reduced speed and higher fuel consumption.

Thirdly, the bearings should not be rigid, but should absorb vibrations from the engine. A running diesel engine vibrates considerably - especially at low engine speeds. Without the damping, these vibrations would be transmitted to the entire hull. The result would be loud humming throughout the boat, rattling of cupboards and crockery, increased wear on all connections. The rubber buffers in the engine mounts are designed to absorb these vibrations and prevent the hull from becoming a resonance chamber. These three requirements are in a tense relationship. Hard mounts transmit power efficiently, but hardly dampen at all. Soft bearings dampen well, but yield too much and waste energy. The rubber must therefore have the right elasticity - matched to the engine weight, power and torque. This is why there is no universal solution; manufacturers specify specific mounts for each engine. The right choice is crucial: bearings that are too hard lead to vibrations and noise, bearings that are too soft lead to energy loss and excessive movement of the machine.

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Recognising wear and tear prevents major damage

To ensure that the drive functions reliably, the engine bearings must also be maintained. Oscillating elements are wearing parts. The rubber ages due to mechanical stress, heat, diesel and engine oil as well as salt water if there is a leak in the cooling water pump. Over time, it loses its elasticity, becomes brittle or tears. Recognising wear is important in order to avoid major damage. Visible damage to the rubber is the most obvious warning sign: cracks, breaks or flaking in the material, but also deformation - if the rubber looks permanently compressed - indicate wear. During the visual inspection, all sides of the bearings should be inspected, including the underside, which sometimes requires a mirror or torch.

The rubber elements are vulcanised onto metal plates that are screwed onto the engine foundation. If these metal parts corrode, the connection loses its strength. Rusty bolts or rusted bearing plates are dangerous - in the worst case, the bearing can tear off. Chemical attack is just as critical: diesel, engine oil or hydraulic oil attack the rubber. If operating fluids drip onto the bearings, the material swells or becomes soft and greasy. Such bearings have lost their damping properties and should be replaced immediately, even if they still appear intact on the outside.

Not all damage is visible at first glance. If the machine vibrates noticeably more than before when running or the humming in the boat has increased, the bearings are often to blame. The rubber has lost its damping effect. This can be tested by carefully placing your hand on various parts of the hull while the engine is running - if everything vibrates strongly, this is an indication of worn bearings.

Movement and noise indicate the condition of the bearing

Excessive movement of the machine is another alarm signal: When the engine is running, the machine should hardly wobble. If it visibly rocks back and forth, the bearings have become too soft or are partially torn. In extreme cases, a bearing can tear off completely - the machine then hangs only on the other three bearings and moves massively. In this case, stop immediately and repair before further damage occurs to the shaft, gearbox or the remaining bearings.

Noises also provide information about the condition of the bearings. Knocking or clacking when accelerating or changing gear indicates that the machine has too much play. The bearings may have worn through or the threaded rods may have developed play. Some manufacturers also specify replacement intervals that you should be aware of. For example, the manufacturer Ellebogen recommends replacement after 1,000 operating hours or four years. This seems very short - in practice, engine mounts often last much longer, especially on boats that are not used intensively. Nevertheless, this information should be taken into account during the inspection. If you use your boat a lot and drive it for several hundred hours a year, you should critically check the bearings every five to seven years. With occasional use, they can also last longer if they are not attacked by oil or diesel. However, the rubber loses its elasticity over the years, even with little use.

Regular maintenance tasks include a visual inspection: Corrosion on the metal and cracks in the rubber can make it advisable to replace large parts. If the machine is running, you can see whether the bearings still dampen vibrations sufficiently. It is best to try out different speed ranges. If the motor moves too much and transmits strong vibrations, replacement is unavoidable. The screw connections must also be checked and retightened. Ideally, there should be markings to indicate when connections have come loose. If nuts have shaken loose, they must be tightened. For machines with a shaft system, the alignment must also be checked. More on this later.

Preparations for the swap

If the condition of the engine mounts is questionable, they must be replaced with new ones. This can often be done without removing the diesel, but is still no easy task due to the limited space available for screwing.

The correct replacement bearings must be procured before replacement. Ideally, original parts from the engine manufacturer should be used - Volvo Penta, Yanmar and others offer them. However, original parts are often expensive, sometimes costing double or triple the price of alternatives. Suppliers such as Vetus or Ellebogen offer suitable bearings for many common engines at significantly lower prices. Ellebogen in particular has specialised: You can enter the engine model on the website and the appropriate bearings will be displayed. It is important that the bearings fit the engine exactly - the wrong weight or hardness can lead to problems such as increased vibrations or uneven load distribution.

Even if only one bearing is visibly defective, all of them should always be replaced. If the other rubbers have already aged, the load is distributed unevenly - the new bearing is overloaded and the old ones wear out more quickly. The result is that the next bearing fails after a short time and the work has to be repeated. Four bearings are common for larger motors, sometimes only three for machines with a Saildrive.

Replacing the engine mounts

The motor must be supported in such a way that the bearings are relieved and the machine is held securely. There are several tried and tested methods: You can clamp robust squared timber between the motor and the foundation, whereby the load should be supported as close as possible to the respective bearing. The advantage of this method is its simplicity, the disadvantage is that you have little working space and the wood can get in the way when loosening the bolts. A better method is often to support the motor from above: A sturdy squared timber is placed across the companionway and the motor is lifted a few millimetres with tensioning straps. This relieves the load on the bearings without wood getting in the way at the bottom. However, this construction must be very stable - a belt that slips or wood that breaks can be dangerous.

In any case, it is important to only remove one bearing at a time. Never remove all bearings at the same time - otherwise the machine will only hang on the support. The old bearing is removed by loosening the fastening screws on the base and the lock nut on top of the thread. The screws are often stuck after years. Spraying rust remover on the day before helps. When choosing a tool, a large adjustable spanner can provide the necessary leverage. However, a lack of space can also make this impossible. In this case, an impact wrench may provide the necessary force.

Heating can help with very stubbornly stuck screws. When loosening the top nut, make sure that the threaded rod does not turn. To do this, use a second spanner to hold against the base. Once the bearing is free, it can be carefully removed. The new bearing is inserted and initially only screwed hand-tight. If the bearing cannot be removed easily due to the tightness, the threaded rod can be removed beforehand. This procedure must also be followed when installing the new bearing. The height is adjusted using the threaded rod - unscrew enough so that the motor is in the correct position later. Patience is required here: Roughly pre-adjust, tighten, check the position and correct if necessary. Once all the bearings have been replaced, they are tightened evenly one after the other.

Procedure for saildrive and shaft systems

Changing the bearings on Saildrive systems is relatively straightforward. As long as the bearings are all set to the same height and the motor is not tilted, the alignment is correct. After changing the bearings, you should check that the Saildrive is vertical and that the machine is not tilted, but there are rarely any serious alignment problems.

Replacing shaft systems is much more complex. Here, the alignment between the gearbox and shaft must be checked after the bearing has been replaced. This also means that this connection must be loosened before replacement. Even small misalignments or angular deviations lead to increased wear on the shaft coupling and shaft bearings, to vibrations and, in the worst case, to gearbox damage. The alignment is first checked roughly and then with the feeler gauge. The coupling halves must be exactly parallel to each other and must not be misaligned.

If the alignment deviates, the height and position of the engine mounts must be readjusted. Most engine mounts offer adjustment options for this: By turning the nut on the threaded rod, the height of the machine can be adjusted, which is the most common correction. The base plates often have oval holes so that the motor can also be moved in a transverse direction. This allows the machine to be aligned with millimetre precision in all spatial directions, which is necessary for perfect alignment.

It may take several attempts until the alignment is correct: Adjust, check and repeat. This process requires patience and precision. An incorrectly aligned shaft not only causes vibrations and noise, but also wears out the shaft bearings and can lead to costly consequential damage to the gearbox and shaft system. Correct alignment is crucial for smooth engine running, especially on boats with long shafts and several shaft bearings. The bolts and nuts should be secured with threadlocker to prevent accidental loosening.

Does everything fit after the exchange?

After changing the bearings and aligning the engine, you should first test drive it carefully: First let it idle and listen for unusual noises, then drive forwards and backwards at low revs. If there are no vibrations and everything runs smoothly, you can slowly increase the speed. After the first few hours of operation, you should check the fastening screws of the bearings again. Markings with special paint are helpful for this. Another visual check is also useful: Are all bearings sitting flat, are there no gaps anywhere, are all nuts tight? This final check ensures that everything is fitted correctly.

Engine bearings are inconspicuous, but essential for smooth engine running and a long service life of the drive system. An annual visual inspection should be part of your routine: Cracks, deformation, corrosion and soiling can be recognised at an early stage. The bearings should be replaced at the first signs of wear or after seven to ten years at the latest. If you do this yourself, you will save several hundred euros in workshop costs and get to know your boat better. However, checking the alignment of shaft systems is challenging - professional help can be useful here. If the settings were good beforehand, the dimensions can be used as a guide before replacing the engine bearings.

With the right replacement bearings, careful work and a little patience, replacement is possible even in confined engine rooms. The result is a smooth-running engine, less vibration throughout the boat and the certainty that the engine is securely fastened.

How the swap works

1. inventory

The new bearings do not fit the old holes. There is also damage to the engine foundation, which must at least be clarified or repaired.

2. marking

Mark the new position. If the engine is no longer in the boat, there is plenty of room to work. It is more difficult with the engine.

3. adjustment

Many manufacturers use slotted holes. This allows the bearings to be adjusted slightly in the transverse direction. This is important for drives with a shaft.

4. adjustment

The length of the threaded rod determines the maximum adjustment travel. You cannot extend it as much as you like, otherwise the lever will also be too long.

Different forms, same goal

The Ellebogen set for a Volvo Penta diesel. Only one engine mount is required at the rear of the saildrive. Set price: 211 euros. More information: Elbow.com

A single vibration damper for a Yanmar machine from the SVB range. Price: 200 euros. More information: SVB.de

Engine mount for a Volvo Penta MD5 from the Swedish outfitter Moory. Price: 130 euros. More information: Moory.de

Short and sweet: checklist to tick off

Preliminary check

• Visual inspection of bearing: Rubber (cracks, deformation), metal (corrosion), working nuts
• Operating symptoms: Visible wobbling, noises when accelerating/shifting gears
• Change requirementManufacturer's specifications, age >7-10 years or frequent use
• Spare parts: Exactly matching bearings (engine model/carrying capacity/hardness), plan all bearings
• Alignment: For shaft system, allow for alignment after replacement; coupling detachable? Feeler gauge available?
• Work preparationSafe support, tools, access/lighting, mark old heights/positions

Exchange itself

• Relieve the engine: Never loosen all bearings at the same time
• Per bearing: Loosen screws, loosen upper nut, hold threaded rod; remove rod if necessary
• Remove old bearing, insert new one; initially hand-tight
• Rough height adjustment via threaded rod
• After replacing all bearings: Tighten evenly one after the other
• Saildrive: same height, check vertical position
• Wave system: Check alignment of gearbox/shaft roughly + with feeler gauge; readjust height/side; use screw lock

Reworking

• Test run: Idle, then slowly forwards/backwards; check vibrations/noise
• After the first few hours of operation: Tighten screw connections, check marking paint; visual inspection
• Stop criterion: Massive motor movement/bearing breakage → Switch off and rectify immediately