1977 Mercruiser 120 hp I/O

Can anyone enlighten me on the reliability of a merc 120 hp? Do they seem to be a good engine/drive or do they have a ton on inherent mech problems? I know there are a lot of variables but overall would you say it is a good engine/drive setup?

Re: 1977 Mercruiser 120 hp I/O

Yes they are good.Just keep up with the maintainance.J

Re: 1977 Mercruiser 120 hp I/O

In 1999 I bought a 1965 V hull Glassmaster 17 foot runabout from the original owner. It has what must be one of the very first 153 CI 4 cylinder Mercruiser engines. This thing is so old that the Mercruiser stern drive is painted white (factory color back then) and it does not have power trim and tilt. In order to tilt the stern drive up to trailer or beach the boat, one has to go to the rear of the boat, grab the stern drive, manually raise it (heavy), and secure it in the "up" position with a factory supplied steel rod.

The entire boat including upholstry and hardware is original and is in excellent condition. This boat is 45 years old and it is used often during the summer, kinda like a classic automobile. There is no hour meter on the boat, but I guess it has at least 1500 hours. The engine runs perfectly and uses no oil.

Based on my experience, I think the 153 engine is a good bet as long as it has been properly serviced and maintained.

Re: 1977 Mercruiser 120 hp I/O

chuck1947-2008 said:

Can anyone enlighten me on the reliability of a merc 120 hp? Do they seem to be a good engine/drive or do they have a ton on inherent mech problems? I know there are a lot of variables but overall would you say it is a good engine/drive setup?

Click to expand...

Very good and reliable setup. Of course, "good" is only as good as the preventive maintenance.

Happy boating!

Re: 1977 Mercruiser 120 hp I/O

I am the original owner of a '67 Sea Ray IO with the 153 cu.in. 120 hp mercruiser engine. This boat and engine has been very reliable for 43 years. The interior, seats, guages and components are still in excellent condition. The engine has has some routine maintenance over the years but runs great. I have replaced intake/exhause manifold gaskets twice, lifter cover gasket once, fuel pump once, water pump and gasket once, water pump/alternator belt once and rebuilt the carb at least 5 times. I did all this by myself and saved a ton of money. The lower unit water pump, steering cables, and outdrive gears have been replaced over the years by a tech. The engine is truly a remarkable engine made by Chevy and modified by Mercruiser. I think it is sometimes referred as the "IRON DUKE". The only issue that is sometimes annoying is the ignition. After a hard run and subsequent shut down, the engine may not start w/o lifting the cold start lever. This could be fuel percolation due to hot soak or something else since the engine is not ventilated like a car. If the previous owner maintained this engine and outdrive like I have, I would say you should a good boat.