Causes of large throttle clearance of freight cars

1) If you mean that the diesel engine is turned off and started, will the valve clearance become larger or smaller after running for a period of time?

The answer is: smaller!

The reason is:

The valve mechanism changes from cold to hot. From the cam and tappet in front of the rocker arm to the valve stem behind the rocker arm, the gap between the rocker arm and the valve stem will naturally become smaller. This gap is called valve clearance.

You must understand that if you adjust the valve clearance too small when the car is cold, you are in danger of not closing the valve correctly when the car is hot. Why? It's simple: both parts are long, so isn't the gap between the two parts smaller? Also, why is the clearance of the exhaust valve always greater than that of the intake valve? Because the exhaust valve is heated more than the intake valve, its expansion is also greater than the intake valve. The bigger the expansion, the smaller the gap will be. If the gap in advance is not enough, the gap may disappear when the car is hot. Do you understand?

2) If an engine changes from new to old, or after several days of valve clearance adjustment, will the valve clearance become larger or smaller?

Answer: It's getting bigger and bigger.

Reason: The wear of parts becomes shorter, and the gap in the middle naturally becomes larger.