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Why was the voltage low when ign on and engine not running? Shouldn't it be nearly the same as engine running? Maybe the coil is internally shorted? That would cause it to heat up, I would think. Reducing the voltage to the coil is done to reduce the burning and pitting of the points. You...

Maybe the engine was sunk?

The first issue is getting a replacement steering rod. Merc upgraded to a SS version, which would not fit my '93 Merc V6. I found a used stock one in Green Bay, WI. It was like new, due to freshwater useage.. A shop may not want to search around for a used part, for an old motor.

Replacing the steering rod (actually swivel pin is it's official name) is a PIA. You pull the gearcase. You pull the powerhead. You remove the exhaust extension. On most saltwater motors, you need to cut the rubber mount bolts at the steering rod, 'cause the rubber mounts are rusted to the...

Sounds about right. Those older Mercs had issues with insulation falling off the wiring harnesses. You might also look for that. CDI Electronics should make replacement components.

The reed stops are real corroded. That should not be. The pistons look fine, from the angle of the photos. The top inside of the cylinder looks like it was beaten with piston material. Maybe the pistons were replaced?

Well, your electrical cables are likely not good, somewhere. Look for corrosion under the insulation. Check the battery switch for corrosion. Remember it does not take too much resistance to cause voltage drop on a 12V system.

That is shocking that a new rectifier was bad. I doubt I would even think to test the new part. Did you test the bad part? I would be interested on what is not working.

The 70HP motor would have 3 cylinders, I would think. The 75HP powerhead may have 4 cylinders, depending on the year. I expect the years to be quite different, I will guess early 70s for the 75HP powerhead. You will need to count and measure the powerhead mounting studs and see if they are...

Check the bottom yoke #7, top picture for play. That is usually where it is. The steering rod #9 top picture, on my '93 Merc rotted out just above the yoke. The cure was to replace the carbon steel steering rod. Also check the rubber mounts. The four bolts from the steering rod and yoke...

You need to run a 50::1 gas/oil mix until you are sure the oil injection system is working. I would test for spark first, as that is the easiest. Check for a kill lanyard, as most controls have a switch/lanyard combo. If the switch is off, spark is killed. A compression test would be next...

Nah, good old HI.

Outboards as usually frame ground (or earth). That means the rectifier or VR will have the negative side of the battery and rectifier grounded. On Merc rectifiers, the negative side of the diode bridge is internally connected to the metal of the rectifier and when the rectifier is bolted to...

You can buy a new rectifier for a few dollars that has much more capacity then the OEM one. i.e. you can get a 25A rectifier that the engine cannot fry. Take a look on Amazon for such an item.

I do not believe that a stator will be damaged, if not connected to the VR or some load. In that case the stator is an open circuit, and no electricity will flow. If the stator is grounded, current will flow. I do not know if this would damage a stator, and I think it would not. Remember...

My neighbor repowered his 225HP 4 cycle Mercs with the equivalent Tohatsu model. He was under the impression that Tohatsu made those 225HP motors for Merc, for cheaper than the Merc model. Any G2 on that?

Let's clear up misconceptions. Non-permanent magnet alternators are used in engines because they charge more at low RPM, when compared to generators. However, they require some back voltage to energize (excite) the rotor, to produce any electricity. They produce AC voltage with the...

Gee, I have been using a hand impact driver to tighten and loosen gearcase screws since the 70's. I never had a screw loosen up and fall out, nor have I had one that would not come out.

OMC made their reputation in the 60s-90s. They made great motors. The big twin was one of those in HP from 6 to 40. They introduced new 2 cycle HPDI tech which failed. They paid the price. Run your motor until it will not run.

Gee, pull all the spark plugs and put a strap wrench around the crank pully and see if she will rotate smoothly.