I realize that my recently acquired 1975 OMC 120 I/O is not the finest of boat engines or drives. But I'm determined to make a reasonable effort to save it. The problem now is figuring out "reasonable." So, it's a 75 OMC 120. Sat for 8 years. I imagine the tarp wore out after about 3 years, which means 5 years in a wet environment (Puget Sound area). Wouldn't do anything at all when I got it. Here's what I've done and where it's at: put a battery in (have also tried jumping it from a working car); pulled, cleaned, partially rebuilt the starter motor, bench tested it with the battery in the car it advanced the gear and spun beautifully; replaced "assist solenoid" which made the cleaned up starter at least try to move; removed the plugs, and cylinders have been soaking (plugs very rusty on outside, but the working end shows just normal wear and build up); pulled and rebuilt carburetor (not that I'm expecting to put any fuel in it any time soon, it just needed done); pulled alternator (was crunchy and definitely adding to load); and most recently removed the sterndrive.
When I turn the ignition now I get a solenoid click and the starting motor creats a loud "thunk" which I believe to be starter motor gear impacting flywheel ring gear. Then a touch of electric motor whining, but no movement. When I do this I observe no movement of the crankshaft pully. BTW, tried to use the serpentine belt to move the crankshaft via pully (before removing alt), but no luck that route. Water pump pully spins freely. Checked the transmission/throttle interlock. When I put the shift lever in gear, no ignition, when I put it back in neutral, ignition causes starter "thunk," shift lever is very stiff, hard to move, but starting to loosen up.
Removed sterndrive, exposing ball gear. I put a steel bar in the ball gear teeth and tried to rotate it. When standing behind the boat, facing the transom, I tried to rotate it counterclockwise which I believe to be the correct direction since I think the drive shaft is coupled directly to the crankshaft. I get a tiny bit of play between the ball gear and the shaft, but the shaft will not rotate. The intermediate housing oil fill screw (large screw with slot for driver on top of interm housing very close to transom boot) will not come loose. It's been soaking in PB Blaster but I doubt any of that is getting past the screw head/gasket and to the threads. So I have no idea of the condition of the oil in the intermediate housing.
My questions, for which I am here to beg answers:
(1) I'm down to I think two options: the engine is seized or the drive shaft is seized (or both); how do I continue the diagnostic process to figure out which it is and/or try to unseize either or both?
(2) Two related questions: Are there any tricks for loosening that big oil fill/drain screw on top of the intermediate housing? or is there another way to access the intermediate housing drive shaft space so I can look for corrosion/rust?
(3) Is there something else keeping the engine from turning that I haven't even thought of? I haven't pulled the rocker arm cover or the push rod cover because I don't have gaskets for those. Should I check them? Seems like the motor would still turn even if the valves were stuck but I don't know for sure.
I would really appreciate any help I can get. I'm a so-so mechanic on land, and boats (other than human powered) are new to me. But I'm a big believer in NOT throwing stuff away just because it needs repaired. So, I remain hopeful.
When I turn the ignition now I get a solenoid click and the starting motor creats a loud "thunk" which I believe to be starter motor gear impacting flywheel ring gear. Then a touch of electric motor whining, but no movement. When I do this I observe no movement of the crankshaft pully. BTW, tried to use the serpentine belt to move the crankshaft via pully (before removing alt), but no luck that route. Water pump pully spins freely. Checked the transmission/throttle interlock. When I put the shift lever in gear, no ignition, when I put it back in neutral, ignition causes starter "thunk," shift lever is very stiff, hard to move, but starting to loosen up.
Removed sterndrive, exposing ball gear. I put a steel bar in the ball gear teeth and tried to rotate it. When standing behind the boat, facing the transom, I tried to rotate it counterclockwise which I believe to be the correct direction since I think the drive shaft is coupled directly to the crankshaft. I get a tiny bit of play between the ball gear and the shaft, but the shaft will not rotate. The intermediate housing oil fill screw (large screw with slot for driver on top of interm housing very close to transom boot) will not come loose. It's been soaking in PB Blaster but I doubt any of that is getting past the screw head/gasket and to the threads. So I have no idea of the condition of the oil in the intermediate housing.
My questions, for which I am here to beg answers:
(1) I'm down to I think two options: the engine is seized or the drive shaft is seized (or both); how do I continue the diagnostic process to figure out which it is and/or try to unseize either or both?
(2) Two related questions: Are there any tricks for loosening that big oil fill/drain screw on top of the intermediate housing? or is there another way to access the intermediate housing drive shaft space so I can look for corrosion/rust?
(3) Is there something else keeping the engine from turning that I haven't even thought of? I haven't pulled the rocker arm cover or the push rod cover because I don't have gaskets for those. Should I check them? Seems like the motor would still turn even if the valves were stuck but I don't know for sure.
I would really appreciate any help I can get. I'm a so-so mechanic on land, and boats (other than human powered) are new to me. But I'm a big believer in NOT throwing stuff away just because it needs repaired. So, I remain hopeful.
