Section 2 Cooling System - ZONGSHEN ZS125-86 Service Manual

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Table Of Contents

Table of Contents

The engine is an internal combustion engine operating at high temperature. Many parts on the engine

are subjected to a considerable heat load, especially the cylinder head, cylinder block, piston, valve and

other parts are in high temperature gas state. Improper cooling measures will cause the engine to overheat.

Parts withstanding high temperature are easy to burn out, while the interoperable parts will be subject o

extremely poor fit clearance due to thermal expansion. Excessive temperature can also cause deterioration

of the lubricating oil, resulting in damage to the engine. Therefore, a high-efficient cooling system is very

important for the engine.

The main function of the engine cooling system is to take away the heat on surfaces of high-

temperature parts, so that the engine temperature is controlled within the allowable range. The motorcycle

cooling system is the water-cooled type

1. Structure and Working Principles of Cooling System

Water pump: as the power source of water cycle, it is driven by the engine. Water-cooled motorcycles

generally use centrifugal water pumps. Water jacket: water jacket is the place where the water exchanges

heat with high-temperature parts, generally arranged around the cylinder block and cylinder head.

Radiator: exposed to the air and right on the upwind section of the motorcycle, the radiator emits the heat

of high-temperature water gained from the engine to the air, and then the water becomes low-temperature

water.

Working Principles of Water Cycle

The low-temperature water in the radiator is pumped into the water jacket through the water pump, and

becomes high-temperature water after exchanging heat with high-temperature cylinder block and cylinder

head, and then flows into the thermostat. At this time, according to the level of water temperature, the

water is cycled in two ways:

[1.]When the water temperature is lower than the specified value, the thermostat valve is closed, water

from the water jacket flows into the radiator for the water cycle through the low-temperature water outlet.

The low-temperature water outlet has a very small cross-sectional area, so the flow of circulating water at

this time is very small.

[2.]When the water temperature is higher than the specified value, the expansive monomer feels the

water temperature and expands to hold out against the piston. As the piston is fixed, so the piston sleeve

drives the valve to move down. In this way, the valve opens, the water flows simultaneously from the high-

temperature and low-temperature water outlets to the radiator, the flow becomes larger and the cooling

effect is strengthened.

When the high-temperature water flows into the radiator, the water temperature decreases, and the water

flows back to the pump for re-cycling. At the outlet of the radiator, a temperature control switch is provided

to monitor the water temperature of the water cooling system and show to the driver at the instrument

cluster.

Working Principles of Water Amount Control

To ensure the proper operation of the water cooling system, it is necessary to secure a constant water

amount in the circulating water path. The water tank or the motorcycle is generally marked with a cooling

water amount. The cooling water amount of this motorcycle model is: 800 mL. The upper part of the water

tank has a vent. The tank and the radiator cover control the water amount in the circulating water path

through the siphon. The radiator cover has the function of automatically adjusting the amount of water in

the circulating water path. It works by the following principles:

[1.]When the water temperature in the path is too high, causing the water pressure to exceed a specified

value, the pressure valve opens automatically and some water retreats to the water tank.

[2.]When the water temperature in the path is falling, it will have a larger negative pressure. If the negative

pressure dropped to the specified value, vent valve opens and the water in the water tank flows to the path

due to siphon effect.