No compression in number one cylinder

Let's start with a guide that runs through compression as that will help explain how to figure this out.

https://www.2carpros.com/articles/what-is-engine-compression

Since we know that we have no or low compression the we need to do a leakage test. This will tell us where the compression is escaping.

Here is a guide that covers the possible causes of this but basically it is a valve, head gasket, or piston ring:

https://www.2carpros.com/articles/symptoms-of-low-compression

Let's run through a leakage test and find out where the compression is going. If it is through the intake then the intake valve is the issue. If it is coming out of the exhaust, it is the exhaust valve. Cooling system bubbling shows it is a head gasket. Lastly the oil fill cap is a ring issue.

https://youtu.be/WHli-wLy9_o

Let us know what you find and we can go from there. Thanks