What is the reason for the abnormal noise of engine cold car?

First of all, does this "dadada" abnormal sound occur at the moment of starting or at idle speed after starting?

If there is abnormal noise when the engine is started instantly, there will be no abnormal noise when the engine is idling after starting. Then this fault point is probably the carbon brush fault inside the starting motor. The working principle of the starting motor is that the gear of the starting motor is combined with the flywheel of the engine and rotates at the same time through the operation of the electromagnet after being electrified, and then the engine can be driven to start, and the gear will quickly return after the engine is started. This fault is because the gear of the starting motor does not return quickly, resulting in abnormal sound of the flywheel, so it is necessary to check the starting motor.

In order to reduce the probability of this failure, when you can turn the ignition key to start the vehicle, do not turn the key for more than 5 seconds. After turning the key, let go quickly and let the ignition key return automatically.

If there is abnormal noise when the engine is idling after starting, this fault point is probably caused by excessive hydraulic pressure and valve clearance in the engine cylinder head. Because there are many kilometers of vehicles and long service time, the engine valve and hydraulic pressure will be worn to some extent. After the gap is too large, there will be a "beep" sound. To solve this problem, it is necessary to disassemble the cylinder head to replace these two parts.

The way to slow down this fault is to change the oil regularly. Don't use engine oil excessively, because excessive use of engine oil will make the lubricating effect of engine oil worse and accelerate the wear of valves and hydraulic pressure.