1972 Mercruiser 120hp 4cyl revival project

[airman1094]

Well I did it again...acquired a new boat (to me) for free(the good part). The bad part is it has been 5 years or so since it ran last. The boat itself has rotted decks but before I start the rebuild I'd like to revive the power plant to ensure I don't rebuild the deck for nothing! I'm very familiar with reviving outboards but this is my very first outdrive rig. I already know to change oil, plugs, gas, and that very rotted looking alternator belt :lol:! What else should be looked over prior to trying to start it? It's in a 18' Mark Twain and the fuel tank is in the bow. What is the easiest way to drain the tank of any possible old gas? I really don't want any junk clogging the lines or the fuel pump. Normally I'd just take out the tank but it doesn't look easy to get to :facepalm:. I know outboards have impellers providing cooling water an the v4 mercruiser has an internal water pump, but does the lower unit have an impeller as well? Forgive the ignorance just not very familiar with these boogers...don't seem too far different in principle! Thanks in advance guys!

 

[Fishermark]

Re: 1972 Mercruiser 120hp 4cyl revival project

Take at look at the top of the page in the "stickies" section. You will find a lot of good basic info on i/os and Mercruisers. Yes, there is an impeller in the lower unit. That's where the water pump is. The engine "water pump" is generally referred to as the circulating pump to avoid confusion.

 

[airman1094]

Re: 1972 Mercruiser 120hp 4cyl revival project

Take at look at the top of the page in the "stickies" section. You will find a lot of good basic info on i/os and Mercruisers. Yes, there is an impeller in the lower unit. That's where the water pump is. The engine "water pump" is generally referred to as the circulating pump to avoid confusion.

Good info! Thanks!

 

[airman1094]

Re: 1972 Mercruiser 120hp 4cyl revival project

Update! I was able to get her to crank and it runs great! Power T/T works great! I've replaced the impeller and all relevant seals associated with the lower assembly! The old impeller was completely destroyed and somewhat melted! Now great water flow to engine. Missing an exhaust boot between the riser and exhaust pipe that runs to the bellows...water got sprayed everywhere but the test proved successful...ran the motor for about 5-10 mins...enough to get it to operating temps! Now I will commence redecking her this weekend!

 

[stonyloam]

Re: 1972 Mercruiser 120hp 4cyl revival project

Sounds like it got pretty hot, so the exhaust shutters are probably gone too, would want to replace them when you do the engine exhaust bellows.