Buying an outboard motor with your hands is always a lottery, where you have a high chance of running into hidden defects, unless you have a proper diagnosis. The inability to start the engine on water often becomes the main problem that scares potential buyers or, conversely, pushes them to rash deals. 90% of malfunctions You can even spot it on the dry shore using only a basic set of tools and attention.
In this article, we will discuss a detailed algorithm of actions that will allow you to weed out frank junk and find a really working unit. You will learn to determine the state of the cylinder-piston group, the tightness of the crankcase, the health of the ignition system and the integrity of the lower unit without having to start the engine in a barrel or reservoir. This knowledge will save you tens of thousands of rubles and save you from buying a “disposable” iron.
The rule of thumb when inspecting is don't believe the seller's words, "The engine worked yesterday," or "We just need to clean the carburetor." Only the facts obtained during the inspection matter. Two-stroke and four-stroke The engines have their own diagnostic nuances, but they share a common base, and that's where we're going to focus. The preparation for testing begins long before you touch the hummel.
Visual inspection and analysis of the external state
The first thing that catches your eye when you meet a salesman is the general look of the unit. The scuffs, chips and scratches on the lower unit and anti-cavitation stove tell you less about the age of the engine than about the culture of operation of the previous owner. If you see deep bullies or missing edges on the propeller, it's a signal that the engine was often operating in harsh conditions, perhaps in shallow water or among rocks, which could damage the engine. gearbox.
Pay close attention to the locations where the lower unit mounts to the lower unit leg, where the presence of traces of rust leaking from under the gaskets or whitish plaque (aluminum oxidation) in these areas often indicates that the engine has overheated in the past, and overheating may have occurred due to the intake of algae into the cooling system or the impeller's failure. Even if the seller claims to replace the pump, no one can guarantee that the geometry of the block heads is not broken.
⚠️ Warning: If you see traces of fresh oil or gasoline for an outboard motor on the ground, it is a sign of leakproofness of the crankshaft or gaskets, and buying such an engine will require immediate and expensive repairs.
Look at spark plugs. The color of the spark plugs can tell you about the combustion processes inside the cylinder. The normal color of the electrode and threads is light brown or grayish. Black, oily plaque indicates a rich mixture or wear of piston rings, and white plaque indicates a poor mixture and the risk of overheating. By twisting the candles, you can also evaluate compression using the primary method, which will be discussed below.
Diagnosis of the cylinder-piston group and compression
The state of the CNG is the heart of any internal combustion engine. To check, you'll need a candle key and, preferably, a compressometer, although experienced craftsmen often do without it. First, unscrew all the candles. If the candles are boiling, use penetrating lubricant, but act carefully so as not to break the thread in the block head. The presence of a spark is checked by pressing the candle thread to the "mass" (the metal part of the engine) and sharply jiggling the starter.
Finger compression testing is an old but effective method. Close the candle hole with your thumb and pull the starter abruptly. You should feel a strong, elastic pressure knocking out your finger. If the finger feels almost no resistance or the air comes out weakly, it is an alarming sign. Low compression can be caused by wear and tear. piston-ring, a cylinder slack or a piston burn.
A more accurate method is to use a compressometer. Roll the device instead of a candle and turn the engine several times with a starter. For two-stroke engines, values in the range of 7-9 atmospheres are normal, for four-stroke ones - 10-12 atmospheres and above. It is important that the range of readings between the cylinders does not exceed 1 atmosphere. A large difference indicates uneven wear or defects of a particular cylinder.
Why can compression be low on a cold engine?
On a cold engine, the gaps between the piston and the cylinder are greater because of the temperature expansion of the metals. So the cold engine compressometer readings can be 10-15% lower than the actual operating values. Warming eliminates this effect, but you can not start the engine without water, so focus on the minimum thresholds for cold start.
If smoke is released from the silencer or carburetor when scrolling with a starter, it means that the cylinder has residual oil or fuel, which is normal after a long downtime. However, if air is forced out of the carburetor or silencer when trying to create a compression (when the candle hole is open), this indicates that the valves (for four-stroke) or petal valves (for two-stroke) are leaky.
Checking the tightness of the crankcase and galls
For two-stroke engines, the tightness of the crankcase is critical, because it is in the crankcase that the primary compression of the fuel-air mixture occurs. The leakage leads to air sucking, impoverishment of the mixture and, as a result, overheating and bullying. You can check this by pressing. You will need a pressure gauge, a pump and adapters to connect to the candle holes.
Close all the holes in the crankcase (inlet, exhaust, blowout windows) and create an excess pressure of 0.4-0.6 atmosphere. The pressure gauge should stand dead. If the pressure drops, look for a leak. Often the air poisons through the crankshaft glands. To localize the place, you can use a soap solution, applying it to the joints of the half of the crankshaft and the exit of the crankshaft.
When checking the tightness of the two-stroke, slightly turn the crankshaft in different directions. The osseils can keep the pressure in one position, but start to soak when turning the shaft, which will indicate their wear or production of the landing place.
For four-stroke engines, checking the tightness is also important, but the emphasis shifts to the lubrication system. Check the oil probe: its color and consistency. The milky shade of the oil indicates that antifreeze or water enters the crankcase, which means a breakdown of the gasket or a crack in the block. Metal shavings on the probe are a sign of critical wear on the liners or rods.
Pay special attention to the petal valves in the inlet of two-stroke motors. They should fit tightly to the body and open only inwards. If the petals have cracks, chips or loosely closed, the engine will start poorly and lose power. Visually, through the carburetor (removing it), you can assess their condition by carefully opening the throttle.
Diagnostics of the ignition system and electrics
The electrical part is what most often fails after winter storage or moisture. Start by checking the spark. Roll in a new, obviously serviceable candle, press it with a thread against the mass of the engine and sharply pull the starter. The spark should be bright, blue-purple and skip between electrodes with a characteristic crack. A weak, orange spark or lack of it indicates problems in the system.
Check the high-voltage wires and caps, they should not be cracked, through which the spark can penetrate the mass, in the dark or just squinting, you can see the leakage of current through the enclosure of the lobe, also inspect the stator and flywheel (if available), the presence of traces of overheating (blue) on the stator coils indicates that the system is operating in an abnormal mode.
In modern electronically controlled motors (CDI, TCI), it is important to check the integrity of the stop switch (emergency stop buttons). If the motor does not stop when pulling the check or turning off the button, it is dangerous to operate it. Check the resistance of the ignition coils with a multimeter, comparing the readings with the data from the service manual for a particular model. Yamaha, Mercury or Tohatsu.
☑️ Electrical checks
If you have a spark but it's weak, try replacing the capacitor or the ignition coil if it's easily available. Often the problem is these elements, but if the situation doesn't change after the components are replaced, it might be the flywheel, where magnets could demagnetize, which is what happens when you hit them hard or overheat.
Inspection of lower unit, Reductor and Cooling System
lower unit is the link between the engine and the water, and its integrity has a direct impact on safety. Look carefully at the lower unit leg for dents, cracks and welding marks. Even a small crack in the area of the lower unit pipe can lead to water entering the exhaust system and further into the cylinders, which will cause a hydraulic shock.
Checking the gearbox begins with a visual inspection of the osteologic paddle shaft. If you see oil leaks around the shaft, the osteologic requires replacement. Also unscrew the drain and control plugs of the gearbox. The leaking oil should be transparent and have a characteristic smell. The presence of an emulsion (“mayonnaise”) indicates that water enters the osteologs, which leads to corrosion of the gears and bearings.
| Verification parameter | Normal. | An alarm signal. | Probable cause |
|---|---|---|---|
| Oil in the gearbox | Transparent, viscous | Emulsion, water. | Wear of the gums |
| Rotation of the screw | Smooth, with light resistance | Crunch, jams. | Damage to bearings |
| Luft screw | Minimum | A tangible knock | Wear of slats or bearings |
| Thermostat (visually) | Absence of corrosion | Strong salt deposits | Seawater work |
The spinning of the propeller shaft should be smooth. Try to spin the propeller with your hand (in neutral gear). You should not hear crunch, grind or feel jerks. You should also not have a backlash. If the gearbox is humming or vibrating when you scroll, then the bearings or gears need to be replaced, which is an expensive procedure.
The condition of the oil in the gearbox is the most honest indicator of the health of a lower unit emulsion means that the engine was operated with faulty ossels and repair is inevitable.
Analysis of the carburetor and fuel system
A carburetor is the engine brain that regulates the mixture. You often hear hand-held purchases saying, "The carburetor needs to be cleaned." This can mean both simply cleaning the jelly varnish and replacing the worn throttle valves. Take off the carburetor and examine the insides. The throttle valves must fit tightly to the body walls without having a backlash.
Check the rubber seals, diaphragms and needle valves. The rubber tans and cracks over time, which breaks the tightness. If you see sediment, rust or water at the bottom of the float chamber, then the fuel tank and hoses also need to be inspected. Mud in the tank is a common cause of unstable engine operation.
Pay special attention to the interface between the carburetor and the intake manifold. There should be no cracks or gaps. The suction of excess air in this place will lead to the impoverishment of the mixture. Also check the fuel pump (if any), blowing and blowing air into the appropriate connections. The pump membrane should be intact.
⚠️ Warning: Never try to start a motor with the carburettor lid open or the air filter removed for inspection, which can lead to reverse cotton and fire, especially if the carburettor has accumulated vapor of gasoline.
If the engine is equipped with fuel injection (EFI), self-deep diagnostics without a computer is difficult. However, you can check the pressure in the fuel ramp (if there is a connection) and the absence of leaks of gasoline from the nozzles. The smell of gasoline around the intake tract with the engine off is a sign of leaky nozzles.
Final valuation and bargaining
After all the procedures, you'll have a complete picture of the engine. Summarize all the defects you find: piston wear, need to replace the osteoils, condition of the gearbox, electrician. Every item is an argument for lowering the price. outboard motor repair is expensive, and new owners often don't take into account the cost of parts and work.
Feel free to ask questions about service history. When did candles, oil, water pump change? Are there checks or service book entries? Lack of information is also information. If a salesman can't answer simple questions about what oil he poured or how he stored the engine in the winter, that's a reason to doubt his words.
So in conclusion, remember that the perfect used motor is a myth. There's always a little bit of a nuance to be addressed. Your job is to determine how critical these nuances are and whether you're willing to invest in the time and resources to recover. A sound approach to testing will allow you to purchase a reliable fishing or cruising assistant that will last for years to come.
How to store the engine if you do not plan to start it soon?
If you buy the engine for the winter or for long-term storage, be sure to drain the fuel from the carburetor or canned the system. For two-strokes, you can pour a mixture with an increased share of oil into the tank (for example, 1:25) and let you work for a couple of minutes (if possible), or just work out the residues. It is best to preserve the cylinders by pouring some oil into the candle holes and turning the crankshaft so that the oil covers the walls.
Can I test a four-stroke engine without starting?
Not at all, but you can estimate 80 percent of the condition, compression, no emulsion in the oil, scrolling purity (no smoke), sealed valves (vacuum check) will give you an idea of the health of the motor, but you can't evaluate the stability of idle and loaded work without starting.
Is it normal if you scroll the starter out of the muffler smoke?
If the engine has been standing for a long time, a small ball of smoke at first turns is normal (oil that gets into the cylinder burns out), but if the smoke is constantly rolling at every scrolling and smells of burning oil, this is a sign of wear on the oil rings or caps.
What instrument should I bring with me for inspection?
Minimum set: candle key, compressometer, multimeter, flashlight, set of screwdrivers, cloth and a container for draining oil from the gearbox. It is also useful to have a couple of new candles for the test.
Should I buy a motor if I have a lower unit cut?
Absolutely not. Cutting off a lower unit (usually after hitting an obstacle) means breaking the geometry of the entire structure, and even if it is brewed, vibrations and loads quickly destroy the weld or cause the crankshaft to skew, which will kill the engine.