Early 80s Mercruiser 140 running on 2 cylinders and low compression in middle 2.

[JesterOMA75]

I have an early 80s boat my son purchased for us to work on. It was supposedly running last year but other than that we know nothing about it(and nothing about boats). We are mechanically inclined and have worked on cars. After replacing the entire ignition system and adjusting timing, and cleaning the carb we got it running only to find that it was heating up. After removing the lower unit and replacing the impeller we now have a running boat that does not overheat. So we water tested it and it ran very poorly and had a leak somewhere around the transom.

So we got a pressure tester and checked the engine. 120, 40, 40, 110. Seems like the middle 2 cylinders are very low. Also found a tear in the shift cable bellows.

Our next step is to pull the head and check the head gasket and clean/inspect/adjust the valves and replace the shift bellows.

Any words of encouragement or advice?

 

[Bt Doctur]

possible blown head gasket from an overheat or incorrect timing

 

[Benny67]

Shared psi numbers on two cylinders is screaming at you that the gasket is blown between them.

 

[Bondo]

Our next step is to pull the head and check the head gasket

Ayuh,..... Welcome Aboard,...... Hopefully, you won't find a flame cut between the cylinders in the head, or the block,....

 

[Scott Danforth]

the other two cylinders are not stellar either.

as Bondo mentioned, hopefully the block is not fire-slotted between the bores

if your shift bellows is bad, the others are bad. pull the drive, do a bellows job, check the gimbal and u-joints, and check alignment.

 

[JesterOMA75]

So here’s the bad news. The head gasket is definitely trashed. There is a groove cut between the cylinders on the head and it has a small crack in the head where the groove is. Worse the block also has a very shallow grove too. What can I do now? I assume I definitely need a new head. Can anything be done for the block?

 

[JesterOMA75]

Pics attached. Head is toast. Can the block be saved?

 

[Bondo]

Nope,...... It's cracked, 'n now scrap,.....

 

[Scott Danforth]

spend $300-$500 and buy a different 3.0 motor

that one is junk

best you can do is weld it up in situ with nickel rod and a tig welder, dress it off and it may make it until fall, it may fail immediately

 

[JesterOMA75]

My son and I picked up a completely different boat today. This one is a few years newer but needs a new floor. The compression for this engine is 170, 160, 160, 110. Any ideas about the lower compression cylinder? I haven't checked the valves yet and it's been setting for years. Otherwise the boat has it's original interior (1985) and has been well cared for. While we were there he turned it over and it actually almost started (old as heck gas and a dirty carb probably).

Our next task is to change the impeller and go through the outdrive. Get some fresh gas and clean the carb. Then throw on the muffs and see if it runs. Oil looks like new. Block is shiny and un-cracked. Price $500.