Electric Battery Powered Reach Truck

Engine Damage Cause Analysis

Nov 20, 2023

As an important part of diesel forklift, LPG forklift and heavy duty forklift, the engine can correctly understand and analyze the various parts of the engine and the existing problems, which can effectively extend the service life of the forklift. NEOlift will give you a detailed analysis.



Cause analysis of engine damage:

1) The clearance between piston and cylinder is too small

The coordination gap between the piston and the cylinder should be in strict accordance with the provisions of the diesel engine instruction manual. If the gap is too large, it will make the cold start of the diesel engine difficult, and the cooling machine will make the cylinder knocking sound, and the power will decrease. If the gap is too small, it will cause cylinder pulling, cylinder expansion and other failures.

Especially when the coefficient of linear expansion of the aluminum alloy used by the piston is relatively large, the above situation is more likely to occur. When the diesel engine is repaired, if there is no operation manual of the machine. Refer to the matching gap of similar models. The clearance of air-cooled diesel engines is generally slightly larger than that of water-cooled ones. Usually, a four-stroke water-cooled diesel engine with a cylinder diameter of 100mm uses an aluminum piston with a clearance of 0.120 ~ 0.150mm.

2) The piston ring opening gap is too small

The opening gap and back gap of piston ring are too small, the friction between ring and cylinder wall is too large, the carbon accumulation in cylinder is serious, and the strain caused by dirt or oil is not clean during assembly.

The opening gap of piston ring is too small, and the first air ring hits the shoulder of the cylinder liner after the old cylinder is replaced by the new ring, or the opening of the piston ring expands too much during assembly, which is easy to break.

The side clearance is too small, the special tool is not used when disassembling, so that the ring appears spiral, the elastic effect or the carbon accumulation in the cylinder is serious, which will lead to the piston ring bite.

Piston ring opening clearance, side clearance is too large, twisted ring, cone ring up and down the direction of the reverse, and lubricating oil is too dirty so that the oil hole blockage are easy to cause oil channeling.

Piston ring opening gap is too small, the opening impact; The side clearance is too large, and the ring collids with the ring bank; The old cylinder is replaced with a new ring, the first air ring and the cylinder liner shoulder impact, etc., these circumstances will lead to noise.

3) The piston ring is broken

The piston is too skewed in the cylinder, resulting in ellipse and taper, and the upper step phenomenon occurs. The working surface of the inner wall of the cylinder liner often forms uneven wear beyond the limit in the piston ring movement area, generally forming a cone in the reciprocating direction and grinding into an irregular oval in the circular direction.

In the position where the amount of cylinder liner wear is the largest, the ellipticity is often the largest, and the non-contact part between the cylinder liner and the piston ring does not wear, so there is obvious wear step. During the work stroke, the gas pressure forces the piston to move down the stop point, which is changed from reciprocating to rotating, and the pressure on the side of the piston ring to the cylinder liner is the largest in the direction of the crank motion plane, resulting in partial wear of the cylinder liner. That is, the cylinder liner perpendicular to the direction of the crankshaft has the largest amount of wear, the crankshaft is bent, the connecting rod is bent, the center line of the cylinder liner is not perpendicular to the shaft line of the crankshaft, and the axial clearance of the crankshaft is too large, which can cause the piston ring and the cylinder liner to produce partial wear and uneven force and break.

If the bearing gap is too large, the piston pin, connecting rod copper sleeve gap is too large, when there is obvious wear step in the upper part of the cylinder liner, the first gas ring is most easily broken. Stuck on the piston, or the piston pin circlip is broken or detached.



4) The piston and piston ring are dumped on one side and pressed tightly on the cylinder wall

Due to piston deformation, piston hole offset, cylinder honing skewness, connecting rod bending or distortion, crankpin and spindle neck imbalance, then the piston pressure on the cylinder wall is relatively concentrated, local surface, so that the oil film between the cylinder wall and the piston ring becomes thin under great pressure, and even breaks, thus losing lubrication, forming dry friction resulting in cylinder pulling.

5) The fuel injection nozzle (carburetor) is poorly atomized for a long time

The fuel nozzle is the most sophisticated component, and the engine mainly burns gasoline during operation. In the combustion process, due to high temperature, carbon deposits occur on the surface or pores of the nozzle and more gum will also be deposited on the inner wall of the nozzle and the surface of the needle valve during long-term use, affecting the injection effect, causing the nozzle to be blocked and sticky, resulting in oil injection leakage, poor atomization, or even no oil injection. As a result, fuel consumption increases, engine power drops, idle speed is unstable, acceleration is poor and cold start is difficult. Test data indicate that when 10% of the fuel injection is hindered, it will lead to incomplete engine combustion, performance decline, fuel consumption increase and exhaust temperature rise. At this time, the fuel nozzle should be cleaned in time to improve the combustion efficiency of the engine.

6) Piston cooling nozzle port failure

An engine that uses a connecting rod bearing to inject oil into a piston pin injector. Due to various reasons, oil injection cannot be normal, resulting in overheating of the top of the piston, causing the top of the piston to melt and pull the cylinder. (Function of oil: cooling, lubrication, cleaning, sealing, rust prevention)

7) Engine cooling poor supercold operation

An engine operating at water temperatures below 65°C is called cold operation. The engine will start to work if the water temperature reaches a certain level before it is fully operated, or when the thermostat is opened at a low temperature, the cooling water will enter the large circulation too early, which will cause the supercooled operation. When the cylinder wall temperature drops from 800°C to 500°C, the wear of the cylinder liner increases by about 5 times. When the cylinder wall temperature reaches 80°~850°C, the amount of wear is significantly reduced. The temperature of water is too low, the temperature rise of diesel in the combustion chamber is slow, the combustion delay period is long, the combustion process is deteriorated, and the operation performance is poor.

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