Compression numbers with a bad riser

[bshores]

Found some water in the engine oil with little if any in the cylinders noticeable. Compression was consistent all around with the exception of one cylinder near the riser was 25 less. Is this consistent with a leaking riser? Would a bad riser lower compression in one cylinder? A 5.7 volvo. Risers are original and 8 years old. Boat runs normal. Trying to confirm (as much as possible) it is the riser.

 

[wire2]

Re: Compression numbers with a bad riser

If the riser is leaking it would tend to drain into the closest cylinder first. If it's been going on for quite a while, the rings and cylinder wall will be rusty, leaking compression.
Can you remove the riser from the manifold? Look in there with a light and a mechanic's mirror. Black is good, brown is bad.