Category: Inboard engines

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Blown head gasket on your boat engine? Here’s how to fix it!

A blown head gasket is always a pain. You might be enjoying a nice boat trip and suddenly see white smoke puffing out of the exhaust. It could also be that your coolant level is dropping faster than usual or getting mixed with your engine oil. Sometimes, you’ll also notice the engine overheating or losing power. In all these situations, a blown head gasket could be the culprit.

We’ll explain why a head gasket is so important, how to spot problems and what you can do about them. We’ll also explain what you can do to prevent head gasket issues in the future.


Why are head gaskets so important?

At first glance, a head gasket might not seem like much: a thin metal plate with openings for cylinders, oil, and coolant channels. But without a good head gasket, no engine will run properly. So, it’s more important than you might initially think.

The cylinder head gasket is a seal between the engine block and the cylinder head. It prevents gases from the combustion chamber from escaping and ensures that coolant and oil passages between the two parts do not leak. It is therefore a crucial part of your boat engine.

How to spot a blown head gasket on a boat?

When the seal is no longer doing its job properly, gases, liquids, and oil can come into contact with each other. You’ll notice this as a change in how the engine performs. We’ve listed five possible signs of a faulty head gasket.

White smoke from the exhaust

If the head gasket is leaking and coolant is entering the cylinders, the coolant will burn along with the fuel. This often results in white smoke coming from the exhaust. So, if you see white smoke coming from your exhaust, your head gasket might be leaking.

Coolant loss

You’re having to top up the coolant more often than usual, and you can’t see any signs of a leak? Well then, it’s highly probable that the coolant is escaping through a blown head gasket and ending up in the combustion chamber.

Oil pollution

A blown head gasket often results in oil and coolant mixing. This can cause the engine oil to turn into a creamy substance. Some people liken it to mayonnaise.

Engine overheating

If there’s a faulty head gasket, air or exhaust gases can also get into the radiator or heat exchanger. This prevents the engine from cooling properly, leading to high engine temperatures.

Loss of power

Because gases can sometimes escape from the cylinders with a blown head gasket, the engine can also lose power. The engine might also run rough or struggle to accelerate.

Causes of a blown head gasket on a boat

A head gasket doesn’t just fail out of the blue. Usually, it’s a combination of factors at play. We’ve listed three potential causes for a blown head gasket.

Engine overheating

Overheating can be both a consequence and a cause of a blown head gasket. We’d go so far as to say it’s the number one cause. When the engine gets too hot, the metal expands under high pressure, which affects the seal.

The wear and tear of the years

With every part of your boat engine, there’s eventually wear and tear. After many years of faithful service, with fluctuations in pressure and temperature, a head gasket can eventually give up the ghost. The gasket is simply knackered.

Incorrect assembly or gasket

It’s also possible that the wrong head gasket has been fitted, or the gasket wasn’t fitted correctly. So always make sure your head gasket is compatible with your engine block and that the fitting follows the instructions in the manual.

What to do if your head gasket’s gone?

If you keep sailing with a blown head gasket, it can lead to bigger problems and, ultimately, hefty repair bills. That’s why it’s wise to act fast if you notice the signs of a potential blown head gasket.

Stop directly with sailing

If you see white smoke, the engine overheating, or oil and coolant mixing, it’s best to stop boating. This will prevent further damage.

Let the engine cool down

Let the engine cool down for a while. Don’t go poking around while the engine is still hot. That would be unsafe. So, have a bit of patience before you get cracking.

Find the problem

Check the coolant level and look at the oil. If the level is significantly low and the oil is discoloured, you’ve probably got a blown head gasket.

Order a new head gasket

Choose a new head gasket to match your engine block. If you have a Ruggerini or Bukh engine, you can order the correct head gasket set from AB Marine Service. For other makes, we’ll refer you to a specialist or supplier.

Fit the new head gasket

Got a knack for tinkering? You can fit the new gasket yourself. If you’re a bit of a novice, it’s best to leave it to a mechanic.

Preventing blown head gaskets in the future

Prevention is, of course, always better than serious damage and high repair costs. If you want to avoid the hassle, we recommend taking a few tips into account. We’ll give you five.

Keep the coolant topped up

First, always ensure there’s enough coolant in the tank. Also, opt for high-quality coolant. This will prevent the engine from overheating unnecessarily.

Check the cooling system

If you want to avoid your head gasket blowing, it’s a good idea to get the radiator, thermostat, and water pump checked now and then. A cooling system that’s working properly will lower the odds of your head gasket giving up the ghost.

Let the engine warm up/strong>

It’s important for every engine to warm up gently. So, don’t go full throttle straight away with a cold engine. That can put too much strain on the gasket. This leads to blown head gaskets, and we want to avoid that at all costs.

Avoid overloading

Cruising at high revs isn’t a good idea either. This increases wear and tear. So, it’s advisable to cruise at a more relaxed pace and avoid running at peak power for too long. This way, you’ll prevent your head gasket from failing, and it’s also better for other engine parts.

Regularly service it

Regularly changing the oil, checking the engine, and addressing minor issues promptly will keep the engine in good condition. So, check the various fluids and make sure there’s no oil in the wrong places. This will prevent problems from accumulating.

Struggling with your packing? AB Marine Service is the place to go

A blown head gasket isn’t the end of your engine. If you spot the problems early, act decisively, and keep up with maintenance, you can avoid bigger headaches down the line. A new head gasket means you’ll be back out on the water, enjoying your boat for years to come.

At AB Marine Service, you’ll find head gasket sets for Ruggerini and Bukh engines. For other makes, we can often arrange parts through our suppliers, but this is always bespoke and not a DIY job.

Order your new head gasket from our shop, or don’t hesitate to get in touch if you’ve any questions. Not sure which head gasket you need? Or perhaps you’ve a query about the repair? We’re here to help with expert advice.

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How to install an inboard engine?

Are you going to install or re-install an inboard engine yourself? Then prepare yourself well, start with the basics and start measuring. Then you can replace an engine with minimal adjustments. For recent engine types, you often know the installation dimensions or they are easy to find. Pay particular attention to:

In any case, consider what you will need.

Propeller shaft height

First check if the engine matches the propeller shaft height. Are the reverse clutch output and the crankshaft at the same height? If the reverse clutch output is lower than the existing propeller shaft, the engine will ‘rise’.

Engine mounts

On some inboard engines, adjusting the existing engine mounts is not a problem. In case of a steel ship its foundation can be adjusted. In a polyester ship, this is more difficult. Therefore, please check in advance what is possible. Especially with a saildrive, you are often bound to prefabricated through-hulls.

Maximum tilt

Also check whether the inboard engine can handle the maximum tilt when sailing. The maximum tilt can often be found in the manual. A homokinetic drive solves the problem in a different way.

Reverse gear

The Velvet, PRM, Hurth, ZF and Twindisc reverse gears are well known common types. The ratio is often given as engine speed divided by the output speed, e.g. in the ratio of two to one (2:1). This ratio means: Two engine revs / one propeller shaft rev (or simply half).

Often the direction of rotation is indicated with L or R. L 2:1 therefore means: a two-to-one left-hand reverse gear for a left-handed propeller.

You may also come across gears, e.g. for Volvo Penta, with an A for Angle. The axis of these reverse gears is rotated by 7 degrees. Then the motor does not have to tilt as much.

Propeller

Note the direction of rotation of the screw. There are left-hand and right-hand reverse gears. The direction of rotation of the gearbox is determined with the ship moving forward and you looking at the bow.

Be careful with a ‘Z-drive’. The engine will then be reversed, so check the specifications carefully.

AB marine service can carry out the power requirements calculation for your ship.

Power

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

If you are going for larger or smaller power, check the diameter of the connection on the engine. This is already a good indication of the required size.

If the exhaust manifold has a 45 mm diameter, you can use that one. Do not use smaller diameters, this will cause the engine to brake, with all its consequences. Bigger ones are often not a problem.

Propeller shaft and bearing

Also think about connecting the propeller to the reverse gear. Some brands are interchangeable, but this is not always the case. In that case you will need an adapter flange. These are available separately on request or are supplied ready to use with a homokinetic drive.

Want to prevent vibration and save time when connecting? Consider the advantages of a thrust bearing with a homokinetic drive.

What do I need?

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Dry and wet exhaust.

The difference between a wet and dry exhaust explained!
Compare a dry exhaust to the exhaust pipe of the car: a pipe with a flexible connecting piece on the exhaust manifold, discharging the exhaust gases directly to the outside air. A dry muffler is often required to muffle the noise. Cooling water from the engine is added to the exhaust system either externally or at a much later stage. The tubes and pipes are often made of steel to prevent them from melting due to the high temperature. It is a simple system, but with two major drawbacks: it emits intense heat of up to 600°C at the source, and it produces more noise.

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Rather a wet exhaust?
What is a good alternative? That’s right, the much talked-about wet exhaust system. It is recognised by the manifold that is mounted on the engine. This is often custom-made from cast iron. It is also recognised by the freezer caps in the cooling channels. The heated cooling water in the engine is around 60-90°C when it leaves the engine, so it can be perfectly used to cool the 600°C exhaust gases. Water and gases are often not yet mixed in the first section of the exhaust pipe. That is to prevent the water from entering and blocking the gases from exiting the engine. Gases must be able to exit the engine smoothly so as not to compromise the engine performance. At a short distance from the engine, the gases and liquids come together and exit the engine.

The difference in temperature of a dry and wet exhaust is noticeable and has many advantages.

The noise of a wet exhaust is muffled by the water, but a rubber exhaust hose can also be used. This gives more flexibility and has a longer life span.

Various cooling systems

In simple terms, there are three types of cooling systems: 1. A system that pumps water straight from outside into the engine block by way of an impeller pump; 2. A separated system, often referred to as an intercooling / heat exchanger system, with coolant in the engine and an impeller pump pumping cooling water through a heat exchanger. 3. A keel cooling system, with cooling pipes containing coolant running underneath the boat. A wet exhaust is not possible in this system, unless an extra pump is installed.

From dry to wet? Convert the dry exhaust if you would like to experience the advantages of a wet exhaust system. Fully assembled exhaust pipes are available on the market. Or just add water to the dry exhaust, where only the first section is not cooled. Conversion may require a fair amount of money, but it is an easy job for the handy do-it-yourselfer and it will pay off in due course.
( wet exhaust system with waterlock and muffler).

A wet exhaust consists of the following components from start to finish:

  • A water inlet pipe underneath the boat with a shut-off valve to stop the supply during repairs or maintenance.
  • A seaweed filter to stop harmful material entering the impeller pump.
  • A suction pump on the engine (impeller or bilge water pump.
  • When conversing from keel cooling to intercooling: a heat exchanger with water-cooled exhaust manifold.
  • A water injection piece, which adds cooling water with an aerator past the exhaust manifold, to prevent the water from siphoning back into the engine when the engine stops.

Also, a so-called Waterlock is recommended when using a wet exhaust. A waterlock collects the water and pushes it upwards through the exhaust with the exhaust fumes by means of overpressure. A waterlock also muffles the noise, because it remains at water level. The gooseneck serves as an extra safety feature to prevent backflow of water when the engine is lower, as is the case in most sailboats. Installation of a muffler is still an extra option. A muffling and flexible exhaust hose can also be used for wet exhaust systems; it can be attached using stainless-steel hose clamps.

Looking for advice on your exhaust system? Please do not hesitate to contact us, or visit our website for various parts.

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A flexible engine set-up

Vibration-free sailing is for relaxation!

Ever made a lovely boat trip, but eased down on the throttle after a while because of all the noise? After all, for a stress-free yarn we want to be able to hear one another. A flexible engine set-up with engine supports will minimise any noise and vibration. But what is the basis of vibration-free (relaxed) sailing? The principle is simple: remove the fixed connection between the engine and the bedplate. This makes that vibration of the engine is felt throughout the boat. Allow the engine to float on its bedplate to get rid of the noise. But how is that done? Start at the base;

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Why do engines vibrate?
Engines have internal parts that quickly move back and forth. It takes only milliseconds for the piston to be pushed down by an explosion and then back up again, driving the crankshaft at the same speed for a new compression stroke. Modern engine blocks are compact and lightweight thanks to a short piston stroke and aluminium construction. This has many advantages, such as saving space and lower production costs. However, due to its lightweight construction, vibrations are less attenuated and absorbed by the dead weight, and the shorter engine stroke also requires a higher RPM to keep running. And we know from experience that the further we open the throttle, the more noise we create.

Detached engine mount
All the more important to ensure a good and solid bedplate with soft engine mounts, which detach the engine from the bedplate, as it were. The principle is an engine mount as soft as possible, but still strong enough to carry the weight of the engine, the reverse clutch and a part of the propeller shaft.The softest possible rubber
The softness of rubber is expressed in SHORE with a hardness number. In addition, the letters A through to D determine the category of rubber, on which we will not elaborate in this article. SHORE 10 rubber is very soft, and the higher the number the firmer it becomes. A heavier engine also needs stronger rubber to make sure that the rubber is not squeezed out by its weight. Engine mounts are often SHORE 35 and up. It is a matter of finding soft rubber that is firm enough to support the engine. Hardness and quality of the rubber often determine the price and lifespan of the product. Good advice! It would be wise not to look at the price when purchasing engine mounts. Cheap engine mounts from other sectors (washing machine mounts) may be able to do the job, but are not always resistant to oil, grease and diesel fumes that we encounter in engine spaces.

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Too soft?
If the engine mounts are too soft, sturdiness will be lost due to the pull and push movement of the propeller shaft and engine when manoeuvring. V-shaped engine mounts lock the engine in place under load due to their V shape. However, since the engine pushes itself against the rubber, it will also lose some of its muffling effect.

But what is the best solution
For optimal muffling, a combination of flat vibration isolators with a thrust bearing would be the best solution. A thrust bearing keeps the propeller shaft in place. It is a bearing that can absorb forces from any direction. It also hangs in rubber and is mounted between the reverse clutch and the propeller shaft. After installation, it has to be set exactly straight and level to prevent overloading of bearings and propeller shaft sleeves. Even better is to put a flexible (homokinetic) joint between the coupling and the shaft, so that even when under pressure and shifting, all parts can still be running stress-free.

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Example of a homokinetic engine arrangement:
propeller shaft; brown
clamping hub; blue
thrust bearing; pink
homokinetic coupling; green
adapter flange; red
engine mount / vibration isolator; yellow

Advice
Looking for less vibration and more relaxation? In other words: a better engine set-up? We suggest you take a good look at the bedplate of your engine set-up and think about possible improvements. We advise to have this done in consultation with our experts. All engine and clutch makes require their own power calculations. Based on such data, we will be able to draw up a plan.

We supply arrangements for any brand, engine model and reverse clutch. Feel free to ask for your own smooth sailing.