1968 mercruiser 120 with MC-1 outdrive

[spinalcracker]

Need some help here guys, I will the best I can to describe.

1. When I put the boat in reverse all it does is grind and the prop hardly turns. Doesn't matter what throttle is at just grinds.

2.When the motor is running I hear a knocking noise but its not crazy loud but loud enough to notice. Does this mean that my engine is knocking or could it be the oil pump, I heard form a friend that the older oil pumps make a knocking noise. Knocking is slow at low throttle and gets faster with more throttle.

3. Where is the temp sending unit located. Not sure if it is the gauge or the unit but my gauge doesn't work.

4. Sometimes when I start the boat it will make the whole boat shake like crazy but at higher throttle it seems to balance itself out the let off throttle and it is fine at idle.

Any info on any of these issues would be greatly helpful

 

[adeneo]

Re: 1968 mercruiser 120 with MC-1 outdrive

1. The reverse gear assembly or the dog clutch is probably worn out, usually the latter. You'll find both on the propeller shaft.

2. knocking noise can be anything from rods to lifters to oil pump (not sure about that one though), depending on the sound it makes.
Hard to tell, but I'll take a wild guess at either rods, bearings for crank or severely worn piston rings causing slap.

3. It's usually right below the termostat housing.

4. Don't know what that is, but it does'nt sound good??

 

[spinalcracker]

Re: 1968 mercruiser 120 with MC-1 outdrive

I was reading the manuel about removing the lower unit shaft and it stated that if it was an EZ-shaft then I had to remove the drive shaft. How do I know if it is an EZ-shaft in the lower unit and if it isn't an EZ-shaft do I have to remove the drive shaft to remove the lower unit shaft to get to the gears?

 

[Fordiesel69]

Re: 1968 mercruiser 120 with MC-1 outdrive

1.) Your cable could be out of adjustment, or the lower unit is worn out. Cables go bad and need adjusted every now and then. If lower unit is worn out, you wil not be repairing it. Source a used lower unit. Any pre alpha / alpha one gen one will work.

2.) GM Inline 4 engines can sound like rattle traps and live VERY long lives. Make a video and will can tell you how bad it really is.

3.) Sender is screwed into the tstat housing. Touch the wire to a good ground and the needle should peg to full hot.

4.) Shakes? Could be simply running rough, or th stringers could be rotted allowing the motor to move around.

 

[spinalcracker]

Re: 1968 mercruiser 120 with MC-1 outdrive

Just was wondering how I check if the cable is out of adjustment? I have time to work on it tommorow and I have looked at the manuel but it doesn't seem very helpful.

 

[spinalcracker]

Re: 1968 mercruiser 120 with MC-1 outdrive

The temp doesn't seem to change after running for a little bit. I grounded the temp sender and the guage went to full hot. So does these mean that I need a new temp sender? Thanks Guys

 

[spinalcracker]

Re: 1968 mercruiser 120 with MC-1 outdrive

I am going to buy a used lower unit for the boat. Is there anything that I have to look for splines, length of drive shaft or anything else?