Volvo Penta AQ131A won't start, very low compression

[Melp22]

I purchased an 86 Bayliner with an AQ131A 4 cylinder engine. The boat had been setting for a number of years. After replacing the starter which was seized, the boat spins over but unfortunately, the boat won't start.

The initial compression on all cylinders was 40, it went up to 45 in two cylinders and 50 in two cylinders after squirting some oil in.

Could this be a timing belt issue?

 

[Scott Danforth]

depending on how long it sat, it could be rusty rings, or stuck rings, etc.

40 psi is rebuild the motor time. your compression should be about 140