The semi-diesel, or hot-head, engine is not a true diesel, but retains the operating functions of the diesel with the exception of high compression. On these engines, the head or a bulb in the combustion chamber is heated to near red heat, usually with a kerosene torch. The engine usually has a manual pump that will force an amount of fuel that will be sprayed through a nozzle in the combustion chamber against the heated area. As the engine is rolled against compression, the manual pump is activated and the sprayed fuel ignites. This in turn creates pressure in the combustion chamber against the piston, thus starting the engine.
Once the engine starts, fuel addition, under pressure, continues automatically and is controlled by the governor. As in a true diesel, the engine speed is controlled by the timing and length of fuel addition, during the power stroke. Also, as in the true diesel engine, this has no throttle on the air intake. Most semi-diesel engines are 2-stroke but there are 4-stroke versions also.
In a semi-diesel, once the engine starts the heat source for the hot-head or bulb can be removed; the heat is generated by the combustion itself to continue the ignition process. Typically, semi-diesel engines have from 5:1 to 7:1 compression ratios. They can use a variety of liquid heavy fuels, from kerosene to heavy bunker oil, and almost anything in between. Their ignition does not come from the pressure generated by the engine as a true diesel does.
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The VOLVO PENTA MD4 is a marinisation of the Mercedes-Benz OM636 engine.
This version is also fitted with a BOWMAN heat exchanger but uses a different sea-water pump.
1. The nitrates, chlorates, and acetates of all metals are soluble in water. Silver acetate is sparingly soluble.
2. All sodium, potassium, and ammonium salts are soluble in water.
3. The chlorides, bromides, and iodides of all metals except lead, silver, and mercury(I) are soluble in water. HgI2 is insoluble in water. PbCl2, PbBr2, and PbI2 are soluble in hot water. The water-insoluble chlorides, bromides, and iodides are also insoluble in dilute acids.
4. The sulfates of all metals except lead, mercury (I), barium, and calcium are soluble in water. Silver sulfate is slightly soluble. The water-insoluble sulfates are also insoluble in dilute acids.
5. The carbonates, phosphates, borates, sulfites, chromates, and arsenates of all metals except sodium, potassium, and ammonium are insoluble in water but soluble in dilute acids. MgCrO4 is soluble in water; MgSO3 is slightly soluble in water.
6. The sulfides of all metals except barium, calcium, magnesium, sodium, potassium, and ammonium are insoluble in water. BaS, CaS, and MgS are sparingly soluble.
7. The hydroxides of sodium, potassium, and ammonium are very soluble in water. The hydroxides of calcium and barium are moderately soluble. The oxides and hydroxides of all other metals are insoluble.
The following is a brief description of a typical seriesOne installation. Detailed instructions are included with each product and should be followed closely.
In short, Cutlass is a type of curved sword and Cutless is a type of rubber bearing although the two are often mixed up.
This type of bearing originated in USA and was manufactured in the 1960’s by a company called Johnson Cutless which is still a registered trade name.The bearings seem to be marketed by DURAMAX who sell them as “Johnson Duramax Cutless Bearings”. In the USA they are still referred to by the full title but others seem to have resorted to the shorter “Cutless Bearing”.
Some insist that the Cutless brand name was a play on words – that they “cut less” than other rubber bearings as the grooves let grit out like the flutes of a drill. Perhaps.
Surely, you might ask, the noise of an engine comes from the exhaust output and not from drawing air in. Well, imagine for a moment the air being drawn into the cylinders of your marine diesel engine. The column of air flowing into your cylinder moves along the pipework rapidly while the valve is open during the intake stroke, and then abruptly stops in its tracks when the valve shuts. The moving column of air suddenly stops flowing in to the engine, compresses a little and bounces back like a spring. This pressure wave travels backward at the speed of sound until it meets a hard surface in the pipework, and then it bounces back toward the cylinder. The air intake then acts like a loudspeaker pumping out vibrations. The pressure wave actually bounces back and forth two or three more times before the intake valve opens again. Just as in a recording studio, these echoes are trapped by closed cell foam in your air intake silencer.
The crankshaft, usually the pulley wheel at the bottom of the engine, usually drives the belts. Belts transfer power to other pulley wheels on the engine and drive the alternator, to provide power to the batteries, and the water pump to circulate cooling water around the engine.
If the belt is too loose:
The alternator may be inefficient resulting in uncharged batteries.
The water-circulating pump may be inefficient resulting in the engine running hotter.
Regularly checking gauges such as the voltmeter and engine temperature will highlight both of these problems.
A slipping or loose belt is often visually indicated by black belt dust around the engine near the pulleys. There are two common types of belt; flat belts or ‘V’ shaped. Consult your owner’s manual about their accurate testing and adjustment, but a common rule of thumb to check adjustment is:
The Volvo Penta MD2030 is what Perkins calls a 103-10. Perkins in turn imported these 100 series engines from a Japanese company called Ishikawajima Shibaura Machinery, Ltd. ISM is part of Ishikawajima Harima Industries, one of Japan’s largest industrial companies.
Perkins marketed this engine in a marinized version as the Perama M30. They sold the engine to Volvo Penta who marketed it as their MD2030. They also sold the engine to Massey Ferguson, McCormick, Terramite, Textron, Jacobsen, Cushman, Vermeer, Leech Lewis, JCB, Kobelco, and Northern Lights to name just a few. In the US, the engine was distributed thru Detroit Diesel – Allison which is closely tied to the MTU conglomerate. By 1996, Perkins had become so successful at marketing these engines to other equipment manufacturers that they formed a joint venture with ISM called Perkins Shibaura Engines, Ltd. and began assembling the engines at the Perkins facility in Peterborough, UK from parts shipped from Japan. In 1997, Perkins was acquired by Caterpillar. With an added boost from Caterpillar, this little engine has become one of the most popular engines in the world. It’s used in turf equipment, tractors, mini-excavators, brush choppers, compressors, welders, pumps, generators and many other applications. Even Caterpillar uses it in some of their smaller equipment. The “Perkins” name was highlighted on the engine ID plate which is located on a distinctive boss just forward of the injection pump. The 2006 model year’s production of the engine has “Shibaura” highlighted on the ID plate. In 2001, the larger Shibaura 400 series engine was introduced with assembling at Peterborough, UK from parts mostly from Japan, and in June, 2004 assembling of the 400 series engine began at a Caterpillar facility in Griffin, Georgia, USA with production exceeding 100,000 units per year.
When two dissimilar metals are in contact (electrically connected), and immersed in an electrolyte (such as salt water) they produce a galvanic cell (like a battery). As current (that is, electrons) flows from one metal to the other, the metal donating the electrons changes form and corrodes. This process is called galvanic corrosion and will quickly destroys underwater metals. The way we counteract galvanic corrosion is to add a third metal into the circuit, one that is less noble than the other two to give up its electrons. This piece of metal is called a sacrificial anode, and in marine engines it is most often made from zinc.
You will, no doubt, be familiar with the shaft anode shown above. The stainless steel of the shaft will cause the Bronze of the propeller to corrode, and so we install a zinc sacrificial anode to prevent this happening. Metals can be placed on a scale – the galvanic scale – to let us know which will sacrifice themselves in any pair. If two metals are in contact in an electrolyte (such as salt water) then the metal which is higher up the Galvanic Scale will corrode. You will notice that Zinc is second from top.
Heat exchangers in marine diesel engines are typically fabricated from a mix of copper alloy and mild steel. These are at risk of galvanic corrosion. To combat this, many heat exchangers are fitted with a zinc “pencil” anode. You will find it usually under a plug or plate within in the exchanger. The pencil is unscrewed from the plug for replacement. Raw water cooled engines have a similar zinc anode inside the cooling-water jacket to protect dissimilar metals in the engine. Determine if your engine and heat exchanger are fitted with internal anodes, and if so, check them at least annually. If they are half depleted then best replace them.
Diesel bug is contamination of diesel fuel by microbes such as bacteria and fungi. Water can get into diesel fuel as a result of condensation, rainwater penetration or adsorption from the air — modern biodiesel (a mix of diesel from fossil fuel and oil from plants) is especially susceptible to water absorption. The presence of water then encourages microbial growth which either occurs at the interface between the oil and water or on the tank walls, depending on whether the microbes need oxygen. Dead bacteria, fungus and their waste products result in a sludge which generally lies at the bottom of the fuel tank. In rough weather, however, this sludge can get mixed up into the fuel and sucked into the primary fuel filter, which can cause fuel starvation and your engine stopping in, remember, rough weather – just when you need it.
There are additive treatments which help to reduce the occurrence of diesel bug. One example is Hydra FuelPlus biocide which “rapidly eliminates all microbial contamination, bacteria, algae and fungi present in fuel tanks without effecting the fuel quality. It stops microbes and promotes trouble free combustion, reduces smoke emissions and improves engine efficiency.” As with most biological growths, Diesel Bug is a temperature related problem and some areas of the world are more susceptible than others. Speaking to your fellow boat owners will help understand the risk in your area.
Remember, the treatment will kill the bug but it will not clear away the sludge. If you have had an infestation in your diesel tanks, then polishing your diesel and steam-cleaning your tanks is the best way to eliminate the residue.
Bio-fuels used today are largely derived from agricultural crops. Sugar cane and corn are used to make ethanol which is mixed with petrol for road vehicles, while bio-diesel is made from vegetable oils like soy. As a renewable resource these products have a positive effect on environmental damage caused by fossil fuel use as they consume carbon dioxide from the atmosphere as they grow. Critics point out, however, that food prices have increased in less developed parts of the world due to increased competition for soy and grain without increased supply.
It is, nevertheless, a reality that the diesel oil available as a fuel today is not the same as that available when our diesels were designed, or even when they were newly installed. Currently regulations vary in different parts of the world but road diesel in the UK is 7% bio-diesel and 93% petroleum diesel.
It is this fraction of your diesel that is prone to absorbing water. Boat owners face a unique set of challenges for storing diesel fuel – at least in comparison to car owners. Typically, cars use their diesel supplies quickly and store it in relative dryness. On boats, the diesel might be months or even years old and any air that enters the tank via the breather pipes will invariably be damp. Damp air in tanks will condense on the walls at night and run into the fuel. In the past, this would sit at the bottom of the tank until the tank was eventually cleaned out. Now, the water can be absorbed into the fuel and transported to the engine. Damp fuel can lead to moisture in the cylinder causing white smoke and corrosion in the engine head.
Think for a moment about the inside of a cylinder in a diesel engine. The inside cylinder wall needs to allow the piston to move up and down at great speed, forming a vacuum and a high pressure by turns. Although the piston is a tight fit in the cylinder, it must not allow the pressurised gases (or the fuel) to leak into the body of the engine and contaminate the lubricating oil. This is achieved by piston rings, which slide up and down between the piston head and the cylinder wall. We obviously want to lubricate the cylinder wall with oil to help the piston rings do their job.
When modern diesel engines are manufactured, the cylinder bores are honed (machined) to produce a “crosshatch” appearance with fine grooves from both directions at about 22 degrees from the horizontal (see below).
The crosshatch pattern is required to retain oil to ensure proper lubrication and to form a seal between the piston rings and cylinder bores. Bore polishing is characterized by a clearly defined area of bright mirror-like finish on the cylinder bore where the crosshatch pattern is worn away (see below).
Bore polishing is caused by a build-up of carbon deposits in the piston top ring land area, i.e. the part of the piston above the top ring. Poor combustion of diesel fuel leads to these hard carbon deposits, which are highly abrasive and scrape away the honing grooves on the cylinder bores. Bore polishing leads to increased oil consumption (blue exhaust smoke) and loss of combustion pressure and performance. This is because the oil film trapped in the honing grooves that maintains the piston ring seal and combustion pressure, is no longer there. Unburned fuel and combustion gases then leak past the piston rings and contaminate the lubricating oil.
There is evidence that operating older style diesel engines with modern high-spec synthetic and semi-synthetic oils, and also running them at constant revs for long periods of time (i.e. in the hours) without varying the throttle can caused bore polishing.
15W40 means that at cold temperatures the oil has the same viscosity as SAE 15W oil. At high temperatures it has the same viscosity as SAE 40 oil. The 15W40 designation means that the oil is a multigrade oil. It has the viscosity of 15W when cold and the viscosity of SAE 40 when hot. This means that one type of oil works in all temperatures. The Society of Automotive Engineers or SAE has established an arbitrary scale for the viscosity of motor oils. The scale ranges from 0 to 60. The numbers from 0 to 25 have the letter W added. This means that they are “winter” viscosity, for use at lower temperatures. The viscosity of a liquid is its resistance to flow. High intermolecular forces between the molecules cause a high viscosity. As the liquid warms up, the added kinetic energy overcomes some of the attractive forces. The viscosity decreases. Hot molasses flows more readily than cold molasses. A single grade oil like 15W or SAE 40 oil has a high viscosity when cold and a lower viscosity when hot. The first number 15W is the viscosity of the oil at cold temperature, and the second number 40 is the viscosity at 100 °C. The 15W40 designation means that the oil is a multi-grade oil. It has the viscosity of 15W when cold and the viscosity of SAE 40 when hot. This means that one type of oil works in a range of temperatures.
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