Final answer:
If the cylinder head gasket is bad, the compression readings in the affected cylinder will be lower than normal.
Step-by-step explanation:
If a cylinder head gasket is bad, the compression readings in the affected cylinder would be lower than normal. The cylinder head gasket forms a seal between the engine block and the cylinder head, and if it is damaged or worn out, it can allow compression to leak out. This leads to reduced compression readings during a compression test.
For example, a normal compression reading for a healthy cylinder may be around 150 psi. However, if the cylinder head gasket is bad, the compression reading in that cylinder may be significantly lower, such as 100 psi or even lower.
It is important to note that low compression readings can also be caused by other factors, such as worn piston rings or valves, so it's always recommended to consult a mechanic for a proper diagnosis.