TOPIC: 1960 Johnson Super Sea Horse 75hp Evaluation (VS4)

I did the water pump, check to the points, and syncd the carb and ignition. I fired it up and got lack luster performance, Im gonna rebuild the carb and fuel pump and give it another shot. Compression is at 80 pounds on all four. I removed the bypass covers and notoced scoring on one of the cylinders, overheating maybe??. I removed the head to inspect. Please let me know what you think. Here is a video.
Thank you
Jim



Any tips and info, is greatly appreciated.

some pics
Thanks

here's another

Why don't you pull the rear pan off? At this point it's only being held on by 2 screws. It will make life way easier. When you say lackluster - was in just run in a barrel? Power testing really has to be under a full load with a propeller or test wheel in a large test tank - or in your case - the boat ramp. Leave the boat fully attached to the trailer & back it into the water with the lower unit and water pump housing fully submerged. The scoring is a bit unusual, because it is on the intake side of the piston. Most damage is normally on the exhaust side. This engine may have been run with inadequate / no oil in the fuel at some point. It also could have been overheated and siezed - if that were the case - the paint on the heads & the block where the heads attach might have a toasty brownish color. Bubbled paint alone is not always an indicator of overheating - but burned paint is a dead give away.

The rear exhaust cover is indeed cooled with water. Inside the engine behind it is a stainless steel plate (aluminum on later engines) that has intensely hot exhaust gases blasting it from the exhaust ports. If it leaks, you need to remove it & replace the gaskets - there are two of them. Any stuck bolts need to be heated severely and tapped with a hammer (using a drift) and allowed to cool before attempting removal. Repeat as many times as needed to get it to move. Be careful - it doesn't take but a few pounds torque to break one off. Some people use penetrating oil - others say not to use it as it will make the bolt even harder to remove.

But getting back to the reason why you took it apart - what did you consider lack luster & why?

Finally - do not pour money into this engine as it is damaged. Snoop around and find another one that has good cylinders and pistons. Good ones without scoring can be extremely difficult to find anymore. Over sized pistons and rings will cost you dearly if you can even obtain them. Then you will need to have the cylinders machined. Now you are looking at around 1 grand just for pistons and machine work

I figured it would sound a bit more like this motor at about 1 min 15 sec in.


The lack luster performance I refer to (probably a bad choice of words) was the hard start, the inability to adjust the slow speed adjustment, and the lack of revs. I guess I wanted it to sound like my Mark 55. I figured I would rebuild the carb, fuel pump, and go over the mag and that would resolve the situation. The reason I took it apart was because I spotted the scoring on the piston. I want to try and make sure I dont have to tear into the powerhead.

If I were to tear into the powerhead, i would prefer some better on gas, maybe another 4 cylinder merc.

I don't mean to sound harsh - but if you didn't want to tear apart the power head, and the compression was even on all 4 jugs, I'm scratching my head on why you tore it down?

You could have tried those easy things you described above first, especially the coil in the magneto. The coil can go bad in these but the engine will still run - just not correctly. Was the engine in forward gear when you tried to wrap it up some? If not, there is a lock out on the throttle and magneto that won't allow the engine to over speed if it isn't in gear. And the only way to get the low speed needles adjusted perfectly is to run the snot out of the engine on the water to clear it out and get it nice and warmed up before fine tuning.

?.........!!

Thanks for the insight, I appreciate it. I hardly think removing the head constitutes a tear down. I would rather take the 2 minutes and remove the 10 bolts and have a peak in the cylinder, than to mutilate my transome mounting something that doesnt have a shot in hell at working out. Based on what I have seen and heard, I think I will reassemble and give it a shot. If it doesnt work out, I'll just clamp the Merc back on. Thanks for your input, it has been extremlely helpful.
Jim

Thanks for sticking with me and my silly questions, I am a novice, but having tons of fun playing with this motor. In addition to the loose carb creating a lean condition in the one and only damaged cylinder as was pointed out to me, is it possible that the loose and frozen exhaust plate bolt in this picture, let exhaust gases seep into the cooling system and cause the upper cylinder in this picture to run hot and get damaged?? Seems odd only one cylinder is damaged.

pic

sorry guys, having trouble posting pics

The exhaust leak isn't good, but I don't think it would cause any overheating issues. Outboards have a fresh supply of cool water at all times, and that usually prevents overheating. This of course requires that the engine is pumping water. Questions are good - not silly. How else are we supposed to learn?

Bruce Gerard wrote:

The exhaust leak isn't good, but I don't think it would cause any overheating issues. Outboards have a fresh supply of cool water at all times, and that usually prevents overheating. This of course requires that the engine is pumping water. Questions are good - not silly. How else are we supposed to learn?

Thank You Sir.