HOW TO REPLACE PISTONS IN AN OUTBOARD？

A typical outboard engine relies on a piston to generate power. When the piston goes bad or loses compression, it needs to be replaced. If the piston is to work properly, it needs to be properly disassembled and assembled. So today we will introduce the disassembly and assembly of outboard motor pistons.

About Marine Piston

The piston is one of the main moving parts of the diesel engine. It operates under high temperature, high pressure and high speed reciprocating conditions and is subject to great mechanical and thermal stresses. Therefore, the piston must have sufficient strength and hardness, excellent thermal conductivity, high wear resistance and corrosion resistance, and thermal stability; the relative density should be small enough to reduce the inertial force. Marine diesel engine piston materials are generally cast iron, aluminum alloy and cast steel.

Technical Requirements For Outboard Motor Pistons

It must have sufficient strength, rigidity, small mass and light weight to ensure minimum inertia force.

Good thermal conductivity, high temperature resistance, high pressure, corrosion, sufficient heat dissipation capacity, and small heat receiving area.

There should be a small coefficient of friction between the piston and the piston wall.

When the temperature changes, the size and shape change should be small, and the minimum gap should be kept between the cylinder walls.

The coefficient of thermal expansion is small, the specific gravity is small, and the wear resistance and thermal strength are good.

Treatment Of Piston Knocking Cylinder

The main reasons for the piston knocking cylinder are as follows:

(1) The clearance between the piston and the cylinder wall is too large. The standard clearance of the piston skirt and cylinder of the WD615 series engine is 0.143-0.182, and the maximum wear limit is 0.35-0.40.

(2) After the engine runs for a period of time, the cylinder piston wears out, and the lubrication is not good. The matching clearance between the piston and the cylinder increases due to wear, and a serious step appears in the first gas ring slightly, causing the piston to knock. The cylinder hits an abnormal sound.

(3) After the piston skirt and the cylinder are running for a period of time, the wear is severe, causing serious rounding and knocking on the cylinder.

(4) Individual connecting rods are deformed due to various reasons, causing the piston to be eccentric, and the gap becomes large and the cylinder is knocked. The piston knocking cylinder will result in excessive engine fuel consumption, engine oil consumption, oil consumption, and poor economy. When the piston knocks the cylinder seriously, it will pull the piston and break the cylinder, so that the connecting rod breaks and the cylinder block is damaged.

The method of judging the piston knocking cylinder:

(1) Oil is cut off by cylinder. Take the method of cylinder-by-cylinder oil cut to determine the position of the knocking cylinder. If the oil is cut to a certain cylinder, the sound will obviously decrease or disappear, and when the oil supply is restored, a clear “click” sound will be heard, indicating that the cylinder The piston knocks on the cylinder.

(2) In order to further confirm that the cylinder piston is knocked, the injector of the cylinder can be removed, a small amount of CD-grade supercharged oil is added to the cylinder (to seal), the injector is installed, and the engine is started. The knocking sound disappears or weakens. After the operation, the knocking sound reappears, and the piston of the cylinder is undoubtedly knocked.

In the case of a piston knocking cylinder, the following methods can be used:

(1) After the engine is started, there is a knocking sound when the engine is running at a low temperature. After the temperature is normal, the sound disappears and can be temporarily processed without further processing.

(2) When the engine temperature is normal, there is obvious knocking sound. Try to avoid high-speed operation and disassemble and repair as soon as possible.

(3) After removing the cylinder head and extracting the piston, it is found that the cylinder is seriously out of roundness or strain, or the clearance between the piston and the cylinder is too large, and should be replaced to replace the cylinder liner, piston and piston ring.

(4) If the link is found to be deformed, it should be replaced as much as possible.

Although the process of disassembling and assembling the piston does not involve extremely technical steps, we still have to carefully confirm each step. If you want to buy the right outboard motor pistons, check out our website!