How to classify a GM 4 cyl marine engine?


Hello everyone. I have just bought a boat as a project. It came with a 4cyl GM inboard motor that the owner knew very little about. I may have bit off more than I can chew, I’ll press on nonetheless. Anyway my problem is, I have no idea what size or model number this motor is so I have no idea where to begin my…

Given your description I think you have a 120HP. 4 cyl. I/O it could be Mercruser or OMC. In either case this is based on a GM Industrial block, but, the engine has many marine parts and components. Like the starter, carb., fuel pump etc. The head and crank are often different from stock GM. There should be an ID plate on the rear of the engine. There is a flat boss with a stamped number that’s on some engines. Merc. uses a metal tag. If the engine is painted black it’s merc. Painted blue or gray it’s OMC. Some automotive parts will work, with a little modification. Depending on the stern drive you can bleed the hydraulic oil or remove the “Lift Gear” to get the dive up. Also, put pictures on-line or get a generic service manual. Most library’s have manuals. Good luck!

Lots of work ahead for you. After 20 years building ships for a living, this can be fun or a headache. Let’s start with the fuel type of the engine, then try to locate all numbers that are on the label plate on the block of the unit. What about the boat ID plate? Also is it an inboard/outboard or all inboard? Length, general condition so on.
As to the seized lift motor, start with penetrating oil and let it set overnight, then try to get the unit to move using some large channel pliers. This may take several tries before it loosens up. Even then I suspect the motor needs to be replaced not just reworked or worked loose. If you can disconnect and remove the lift motor, then you should be able to manually turn the drive and raise the leg. I’m glad to chat and offer the advice. Good luck where are you?

6 Cyl is plenty greater effective than a 4 cyl. greater torque. the 4.0 capacity the displacement of engine in liters. between the terrific engines ever utilized in a Jeep in the 4.0 L in-line OHV 6 cyl, sometimes widely used because of the fact the 4.0 HO. the present 6 cyl utilized in new jeeps is the Chrysler based 3.7 or 4.0 V6. together as those are as effective because of the fact the outdated in-line 6 they do no longer seem to be as torquey at low engine speeds and subsequently do no longer pull besides in the off-street situations Jeeps are fashionable for.

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