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Mercury 700 3 cylinder 2 stroke 70hp

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  • Mercury 700 3 cylinder 2 stroke 70hp

    Hi all,

    I'm a new poster and would appreciate if any of you could put a date to my outboard and offer a bit of further guidance.

    I think its a blue band thunderbolt Mercury 700 3 cylinder 2 stroke 70hp
    possibly made in belgium the serial number is 9197140.

    If anyone could give a date of manufacturer then that'll be a great help.

    Hopefully i'll then be able to track down a service manual.

    I currently know very little about outboard engines but am willing to learn in order to keep the service costs down and get a bit more knowledge.

    Are these motors any good, and are there any major issues i should be aware of?
    Are they easy to work on?

    I am also experiencing a couple of problems, and would again appreciate input from someone more knowledgeable.

    I've had the motor a couple of years but rarely used it due to a young family,
    i don't know its service history but i feel now is the time to bite the bullet and give the engine a good service before i use it a bit more regularly.

    I started the engine up yesterday after a 2 year rest and it started first time I know i will need to change the water pump, is this a straight forward job?

    I've noticed a small oil leak at the bottom of the gear box it seems to be coming out of the propellor housing, would i be correct in assuming a seal has gone - probably the rubbers going brittle through age!

    Also when we last used the boat it developed an intermittent fault and sometimes would not start unless the mercontrol throttle lever was wobbled about. Typically whenever i have tried to trace the fault it has always started but was a tad unreliable on the river last year.

    I think this could be down to a sticky/faulty neutral start switch is this a common problem and is it best to change the switch? or is there correct gap required across the contacts to ensure the right operation.

    The engine iteself appears to be in reasonable condition for its age although the large rods/bolts the engine sits/swivels on are rusty and would benefit from being replaced - can i still get hold of these?

    Thanks in advance for any replies.


  • #2
    Re: Mercury 700 3 cylinder 2 stroke 70hp

    Lets do one thing at a time. 70's 70hp Mercs were OK in my book. Start by doing a simple impeller change, and thats a must. Look here and see if you can get an idea of a year

    Just Google search for a Merc manual...something like
    Mercury Outboard 70 HP Manual..


    • #3
      Re: Mercury 700 3 cylinder 2 stroke 70hp

      Thanks for the reply Scaaty

      reckon you're right one thing at a time.

      I'll be gettting an impeller and a manual at the weekend.

      Are there are tips i should know for replacing the impeller?


      • #4
        Re: Mercury 700 3 cylinder 2 stroke 70hp

        I'm almost 100% sure you have the same motor as I do.

        Mine has been very reliable so far.

        I believe the year is 76-77, check on your lower end unit you'll find a sticker, if you can still read it the year will be on there.

        Good luck.


        • #5
          Re: Mercury 700 3 cylinder 2 stroke 70hp

          ok thanks all for the welcome so far.

          I picked up the impellor and a manual yesterday
          started to drop the lower unit today, put the engine in forward gear
          and removed 4bolts so far, the bolt either side of the lower unit, the one holding the trim tab on and the other one on the underneath pointing up.

          The lower unit has dropped about 6mm but doesn't seem to want to go any further, have i missed anything.

          I assume the shifter just couples itself and does not need anything unbolting.

          Any ideas?


          • #6
            Re: Mercury 700 3 cylinder 2 stroke 70hp

            cancel that last post

            just had another go with a friend
            2 pairs of hands make light work

            the lower unit is now on the benchv


            • #7
              Re: Mercury 700 3 cylinder 2 stroke 70hp

              Adam89k, thanks for the date check,
              sounds like the same type motor,

              Changed the impellor ok
              (the old one wasn't too bad - but better safe than sorry) and all went back together smoothly having checked how it came apart, engine started & tell tale running nicely.

              went on to change the gear oil & upon draining it was full of water in fact for the first second or so it was only water

              took the lower end off again & checked with the manual
              and http://www.marinepartsman.com/Mercur...blies-479.html
              GEAR HOUSING ASSEMBLY, COMPLETE (SERIAL GROUP NO. 4)(PAGE 1) - image attached

              It looks like i need a new upper gasket

              i also have read of a guide sleeve on some mercury's should my motor have one?

              would any of this be a cause of water in the gear oil?

              i am hesitant to replace the oil until i have isolated the problem,
              would it be a case of if the gearbox was full of oil the water wouldn't get in?

              any advice is apppreciated
              Last edited by Arrowflyte; May 11th, 2008, 05:26 PM. Reason: updated


              • #8
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                Re: Mercury 700 3 cylinder 2 stroke 70hp

                pictures added


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