Restoring the power plant after critical overheating or resource production often requires serious intervention in the design of the engine. Waste of the outboard motor It is a complex process to restore the geometric shape of cylinders that may have deformed due to temperature loads or mechanical wear. Unlike car engines, marine units are more aggressively exposed to the external environment and often operate in close to the limiting modes, making control of the condition of the cylinder-piston group critical.
This procedure is necessary when visual inspection or measurements show the presence of bullies, deep scratches or a violation of the shape of the cylinder, called ellipsity, ignoring such defects leads to a drop in compression, increased fuel and oil consumption, and eventually to a complete jamming of the piston. Aluminum alloysThe stainless gas used in modern two-stroke and four-stroke engines have high thermal conductivity, but at the same time are quite soft, which requires jewelry accuracy in their processing.
The owner must understand that the squashing is not just a “drilling hole”, but a high-precision operation that requires specialized equipment and skill of the master. After removing the metal, the surface of the cylinder acquires the necessary roughness to hold the oil film, but still retains the perfect geometry. The critical parameter is the exact selection of the repair size of the piston, which may differ from the standard by several hundredths of a millimeter, which directly affects the resource of the entire unit.
Reasons for the need for squashing
The main reason that pushes owners to carry out expensive scavenging procedures is heat stroke. cooling-system The outboard motor gets clogged with algae or sand, the temperature in the combustion chamber increases dramatically. Aluminum expands faster than steel rings or khon, which leads to the grasp of the metal and the formation of bullies. At this point, the engine can simply stall, and a further attempt to start without diagnosis can finally destroy the block of cylinders.
In addition to overheating, the cause of wear is often poor-quality fuel or a violation of the proportions of the oil / gasoline mixture in two-stroke engines. Lack of lubrication leads to friction of metal against metal, which inevitably leaves traces on the cylinder mirror.
⚠️ Warning: Attempting to start the engine with cylinders lifted or compression falling can lead to the destruction of piston rings and the entry of metal shavings into the crankcase, which will require a complete bulkhead of the engine.
Diagnosing the condition of the cylinders begins with the removal of the head of the block and visual inspection. If you see vertical grooves on the walls that feel like the nail, or if the cylinder has lost its round shape, the slurp becomes the only way to save the block. In some cases, when the wear is too great, it may require a socket or replacement of the unit as a whole, however, for many models, Yamaha, Tohatsu and Honda Remove under the repair size is a regular repair procedure.
Technology of waste and equipment used
The process of restoring the geometry of the cylinders is carried out on special duct machines that ensure high positioning accuracy of the cutting tool. The wizard first performs the defect, determining the maximum diameter of damage and the degree of ellipticality. repair-sizeThe standard step of increasing the diameter is usually 0.25 mm, 0.50 mm or 1.00 mm, depending on the engine design and availability of spare parts.
The scavenging itself is done by carbide cutters that remove the metal layer from the inside of the cylinder, and it's important to note that not only does the damaged area get removed, but it also aligns the entire surface to a perfect circle, followed by a rough scavenging phase. Hong - is an abrasive tool that creates a net of microscratch on the walls of the cylinder of a certain angle of inclination.
The khon grid is necessary to hold the oil on the vertical walls of the cylinder, since without it, the piston rings will work “dry” and wear out quickly.
The quality of honing directly affects the burning of new piston rings. Too smooth surface will not hold oil, and too rough will cause increased oil consumption and smoke. Modern machines allow you to control not only the diameter, but also the angle of the crosshairs of the notches, which is especially important for nickel-coated engines (Nikasil), although such blocks are more often changed whole than wasted.
Features of the block sledding
In cast iron sleeves, the sleeves are easier to handle because the material is more predictable. In units without sleeves (aluminum on aluminum), it is critical not to overheat the thin lintels between the cylinders during processing, otherwise the unit may crack.
Selection of repair pistons and rings
Once the final diameter of the cylinders has been determined, the piston group is selected, and the piston repair pistons are marked with letters or numbers indicating their increased diameter relative to the standard. 0.50 It's very important to use pistons and rings from one manufacturer and preferably one batch to ensure that the thermal expansion is uniform.
When assembly, you need to take into account the thermal gap between the piston and the cylinder wall. For different models of engines, this gap is different: somewhere it is 0.03 mm, and somewhere it can reach 0.08 mm. Installation of a piston with a smaller gap will lead to bullies during warming up, and with a larger one - to knock and loss of leakage. Ring set It must match the height of the piston and the depth of the grooves, so the use of original catalog numbers is mandatory.
The pistons must be warmed up before they are installed. The aluminum expands when heated, and placing a cold piston in a hot or cold cylinder without warming can cause the ring bars or the finger itself to break, and the pistons are usually heated in an oil bath or on a special tile to 60-80 degrees Celsius.
- 🔧 Check the marking on the bottom of the piston - it must match the ordered repair size.
- 🔧 Make sure that the ring locks are arranged according to the pattern (usually with offsets relative to each other).
- 🔧 Use a probe to monitor the thermal clearance at the widest point of the cylinder.
- 🔧 Lubricate the cylinder walls and pistons with engine oil before final assembly.
Instructions for assembly of cylinder-piston group
Building the engine after scavenging requires cleanliness and care. Any speck of dust or sand caught between the piston and the cylinder can destroy the results of expensive welding in the first seconds of operation. Before installing the cylinder block on the crankcase, you need to blow all the channels with compressed air and wipe the surfaces with lilac rags moistened in the solvent.
The pistons are carefully installed so that the rings are not damaged, and these are done with special mandrels or just fingers, if the design permits. The rings must be kept as low as possible so as not to break them. Once the cylinder is placed on the piston, you must make sure that it sits freely, without distortion. The bolts of the mounting of the block head are tightened with a dynamometer key in several steps, following the scheme specified in the manual.
☑️ Assembly checklist
Once the engine is assembled, but before it starts, it is recommended that you turn the crankshaft manually several times, which will help distribute the oil over the friction surfaces and make sure that there are no jammings. If the shaft is spinning hard or you hear a knock, the assembly needs to be disassembled and the cause is identified, and only after making sure that the mechanics are normal, you can connect the fuel system and the cooling system.
| Parameter | Standard value | Repair size 1 | Repair size 2 |
|---|---|---|---|
| Diameter of the cylinder | 56.00 mm | 56.25 mm | 56.50 mm |
| Piston gap | 0.04-0.06 mm | 0.04-0.06 mm | 0.04-0.06 mm |
| Compression | 9.0 - 11.0 kg/cm2 | 9.0 - 11.0 kg/cm2 | 9.0 - 11.0 kg/cm2 |
| Moment of tightening of GBC | 22 Nm. | 22 Nm. | 22 Nm. |
Engine break-in after grout
Starting a wasteful motor is always a stressful moment; the first minutes of work should be idle under constant temperature control, oil pressure (if there is a sensor) and no extraneous noise should be monitored. The breaking in process After scavenging differs from running a new engine in that here only rings to the new walls are worked out, and not all rubbing pairs.
The running time usually lasts from 2 to 10 hours, depending on the manufacturer's recommendations piston group, during which time work is prohibited at full throttle and long work at idling. You need to periodically change the speed, giving the rings the opportunity to properly "sit" in the grooves and rubbish to the hon, overheating during this period is strictly unacceptable.
⚠️ Attention: A sharp opening of the throttle in the first hours after ploughing can lead to local overheating of the piston and the reappearance of bullies, since the oil film has not yet formed completely.
After the initial break-in, it is recommended to replace the oil (in four-stroke engines) and check the tightening of the bolts of the head of the unit, since aluminum can float a little after the first heat cycles. It is also worth checking the compression - it should be stable in all cylinders and meet the data-sheet figures for a new or repaired engine.
The success of the drilling depends on the quality of the equipment and 50% on the correct breaking in - do not force events in the first 5 hours of work.
Common Errors and How to Prevent Them
One of the most common mistakes is to save on the quality of the weed, and trying to do this work on the knee or without the appropriate machines leads to a violation of geometry, the cylinder can become oval or conical, which will cause rapid wear of the rings and a combustible of oil. Vibration. The engine at high revs can also be a consequence of uneven removal of metal.
Another mistake is the wrong heat gap, and many craftsmen put the pistons in the belief that the metal will expand, which is a fatal mistake for modern alloys. The piston has to hang around in a cold cylinder, only then, when heated, it will get into a working position, too tight fit is guaranteed to lead to a wedge.
And remember, clean assembly, using dirty tools, rags and pile, or working in a dusty room, negates all efforts, and microscopic abrasive particles work like sandpaper, destroying khon in minutes, and you have to build it on a clean surface, using new fasteners where you want them.
- 🛑 Ignoring the heating of pistons before installation.
- 🛑 Use old rings with new pistons (rings repeat the old cylinder profile).
- 🛑 Violation of the sequence of tightening of the bolts of the GBC.
- 🛑 Lack of compression control after assembly.
Cost of work and feasibility of repair
When deciding whether to waste, the owner of the outboard motor must assess the economic feasibility. The cost of the work is made up of the cost of the mound itself, the cost of new pistons, rings, gaskets and glands. For low-power engines (2-5 hp), the cost of spare parts and work can exceed 60-70% of the price of a new engine, making repairs economically impractical.
For powerful engines (30 hp and above), the topping up is often the only reasonable way out, since buying a new cylinder block or the entire engine will cost a huge amount.
It's also important to consider the rarity of the model. If the engine is old and parts are difficult to find, a smelting to standard repair dimensions may be the only way to keep the equipment on the go. However, if the unit is cracked or has deep casting defects, no smelting will help, and you will need to replace the unit.
Where to find rare pistons?
For older Japanese engines, repair pistons can often be found at auctions in Japan or ordered through specialized water parts stores, with the prefix "Over Size" in the catalog.
Can I squander the engine block on my own in the garage?
High-quality welding requires a precision machine that cannot be placed in the garage, and the skills of the operator, and self-attempts will lead to damage to the unit without the possibility of recovery.
How many times can you rub the same cylinder block?
The usual repair size is 2-3, further increase in diameter thins the cylinder walls, which reduces strength and heat sink, and the maximum repair size is usually indicated in the service manual.
What is the difference between a two-stroke engine and a four-stroke one?
In two-stroke engines, blowing windows that cannot be touched during squashing play an important role, and the lubrication is carried out with oil from the mixture. In four-stroke engines, there is a separate lubrication system, and the requirements for roughness of the walls may vary.
Do I need to change the crankshaft when squandering the block?
Not necessarily if the crankshaft rod necks are not producing or beating, but if the motor mileage was high, it is recommended to check the condition of the crankshaft bearings and glands.
Why does the engine smoke after smouldering?
In the first hours of operation, the smoke is normal — it burns out the conservation lubricant and the rings are laundered. If the smoke persists after running, it may be that the rings have not worked or that the heat gap is incorrect.