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    Lower Unit Oil Leak

    So finding water in the gear case seems common enough. How do you decide if you need to tear the entire box down, and put in new bearings ? If the gearbox works, the propshaft has no obvious play, what else do you look for to change the response from a basic seal repair, to full tear down ? I...
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    Lower Unit Oil Leak

    What is that hole ? It seems to be in an area between the top and bottom filler holes, so it would always be into the gear oil chamber.
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    Mercury 850 thunderbolt 1974 gearbox check

    I will keep an eye out. Parts are definitely starting to get scarce, and power trim would be great. But progress is OK. I have got the stator off, soldered some new wires on OK, and put epoxy on to hold it all together. The engine end of the boat is almost all rewired, but the new cable to the...
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    Mercury 850 thunderbolt 1974 gearbox check

    Thank you Chris. I knew I had a job on my hands, but this project just seems to keep on growing. Nonetheless I dont mind, I am learning a lot, and when I do finally get on the water I will have a good boat and motor that owes me very little money.
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    Mercury 850 thunderbolt 1974 gearbox check

    I checked the wires to the distributor. They are acceptable. The wire is OK, some minor cracking of the insulation, I will heat shrink new insulation on. But the wires to the alternator stator are just powder. This model has a distributor. I assume I can simply whip the alternator flywheel...
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    Mercury 850 thunderbolt 1974 gearbox check

    I must say I am surprised its not fused out of the factory. Putting the fuse in the hot lead to the control protects the most likely locations for a problem, and a fuse failure would simply remove power, essentially the same as turning the key off. But a short when you did not have a fuse...
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    Mercury 850 thunderbolt 1974 gearbox check

    Good one. I was trying to have as much of the wiring fused as possible, but a fuse failure as you point out could easily result in over voltage from the alternator. Thanks for that.
  8. L

    Mercury 850 thunderbolt 1974 gearbox check

    I will rewire all of it, its pretty easy, and I can add a few improvements over factory design. Heres how I think I will do it.
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    Mercury 850 thunderbolt 1974 gearbox check

    Yeah I did consider just running the cables through a 40mm electrical gland and not using the plug. If I ever need to disconnect it I can easily just cut the cable somewhere inside the hull, and use a strip connector - or even a 5 or 7 way trailer plug for the smaller wires. Its out of the...
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    Mercury 850 thunderbolt 1974 gearbox check

    And to show I have a sense of humour, here is the condition of the wiring loom inside the engine. I will fix this by cutting away the rubber around the internal plug, drilling out the wires, and soldering in brand new wires. I will do all those that dont go via this section of loom at the same...
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    Mercury 850 thunderbolt 1974 gearbox check

  12. L

    Mercury 850 thunderbolt 1974 gearbox check

    As much as you can trust any seller of anything, its done a lot of fresh water work, he says he bought the boat in Taupo, which is all fresh. So only its last few months has been in salt. But the prop was well seized on. I made a puller tool, and used a small Sykes Hydraulic pump. (I welded 4...
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    Mercury 850 thunderbolt 1974 gearbox check

    Now thats good thinking ! I was thinking about getting one of those anyway.
  14. L

    Mercury 850 thunderbolt 1974 gearbox check

    Thanks for the diagram. I see how it all goes together now. I could soon make a tool up to get the retaining nut out I think. I certainly appreciate there is the risk of gearbox failure if its not checked, and repaired as necessary. Any 45 year old motor comes with risk of break down, the...
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    Mercury 850 thunderbolt 1974 gearbox check

    Yes, I am not really wanting to spend too much on this, we posted at the same time so have a look at my cunning Plan B.
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    Mercury 850 thunderbolt 1974 gearbox check

    Yes, perfect instructions thank you. its stuck pretty good. So as I am reasonably sure the prop seal is OK, I will go to plan B. I will replace the water pump, and check the seals on the top of the gearbox. If they are OK, I will just use it, see how the gearbox goes, and check the magnet bung...
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    Mercury 850 thunderbolt 1974 gearbox check

    Thanks, I will go and have a look. The prop took some removing thats for sure. I used a hydraulic puller, and I had it creaking...
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    Mercury 850 thunderbolt 1974 gearbox check

    Morning all from New Zealand. I tried the search function, couldn't find anything. I bought a trailer. It had a boat and motor sitting on it, so I have decided to get it all working. I started at the bottom, let the gearbox oil out. The gearbox was full of water, looks like the fibre washer...
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