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Rebuilding Johnson 70 hp

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  • Rebuilding Johnson 70 hp

    Hi there,

    Im Leo, 20 years old and currently looking into rebuilding the Engine mentioned above.
    In the past I have rebuild a Force 70hp and an Evinrude 9.9, so I do have a little knowledge.

    The reason for rebuilding it is that the Engine blew the bottom cylinder. Upon closer inspection I figured that it was rebuild before, as it has 0.30 oversize Wiseco pistons in it. To my luck the bore looks acceptable, a hone will do.

    What makes me worry is the lower crankshaft journal though, as I can see and feel one bigger, pitted area with my fingernail. The second picture is after a few minutes of polishing with 400 grit and WD 40.

    Now the question is, if there are undersize bearings available or if it is still okay to use after some more polishing.
    The Motor is going to be run on a little 4m runabout for wakeboarding. The main intention is to get a bulletproof motor that
    can run under load for a while.

    Im thinking about raising the compression a little and to go composite reeds for a little more grunt, but reliability comes first. To achieve that goal I would really appreciate the opinion of the experts on here. Would you run it with this crank?

    Thanks in advance, I will try to take as many pictures as possible
    After polishing

  • #2
    Unless you can get a competent machine shop to cut and polish that crank, I think you need to find another. That surely won't do for long. You have two choices in my opinion. First either have it welded up and returned, OR look for another crank. JMHO!
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    Comment


    • #3
      To make that motor reliable you need to mike the bores and if over .003 out of round find a new block or bore .040 oversize. Replace the divider plate as that cylinder has had water intrusion and the crank is junk. There are no under size bearings for OB motors,there was a company that used to be no longer do it .Jet up .002 on mains in carbs also. If its a older 3" bore if it has the I beam rods replace em with the A frame late model rods, and prop so engine is about 500rpm over max so engine is not lugged.
      Last edited by Faztbullet; November 24th, 2018, 06:32 AM.
      When in doubt,Trim it out!!!
      Business Owner & Certifed Technician
      Boats I own & use
      20ft Javlin w/250 Junkrude
      17ft Bullet w/200 Merc (SOLD!!)
      13ft Allison w/150 I-6
      17ft Hydra-Sport 175GT
      15ft Allison w/75 Stinger(project)
      14 x 48 Drifter with 1100SS Merc

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      • #4
        Unfortunately the bearings are but one size... they are no under-size bearings.

        The crankshaft is either perfect or a throw-away item. Perfect crankshafts should be readily available at a fraction of the original cost. This hold true for the related connecting rod also.

        Good luck with your rebuild project.
        Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

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        • #5
          ?----You would need bigger diameter rollers .----They will not fit the cage.---Welding usually bends a precision shaft !!--------To get a " bullet proof " motor you need to find another crankshaft..----Model # is ?

          Comment


          • #6
            Alright, thanks for the fast replies. I just put an ad on Kijiji for a new crankshaft.
            Hopefully I'll get lucky. The Conrod actually looks great, no sign of wear or dicoloration.

            Faztbullet I think this motor doesnt have a divider plate. It appears to me that the block, including the exhaust passage
            is made from one mold. From what I know this is the 56ci.

            Modell Nr: B08928662
            Serial Nr: BJ70TLEND

            I will have the bores mike'd next week I think, but is is possible for the sleeve to be untrue if you can still see the crosshatching clearly?

            Leo

            PS: the crankshaft has the fine spline pattern

            Comment


            • #7
              1992 model----Fine spline started in 1989 year.

              Comment


              • #8
                So would every crankshaft from 89 up fit my engine?

                As I'm planning on ordering parts next week im still not sure whether to use a much cheaper WSM kit or buy Wiseco pistons and buy the bearings and gaskets separately. I wonder how much benefit there would be from the forged pistons.

                Would it also be acceptable to buy just one new Wiseco piston and reuse the other two (skirts look great, just some carbon buildup on the top) if the bores check out okay? Do I comprimise reliabilty here?

                Comment


                • #9
                  Agree 10% on the crank, but would try an O/B salvage yard rather than Kijiji.
                  You might pay a premium over a private sale but it is worth it for such a critical item....IMO.
                  The salvage yards are in the business and are unlikely to intentionally try to "shaft" you....

                  A list of salvage yards is at the top of forum.
                  You know that you are a very poor driver when Siri says : "In 1/4 mile pull over and let me out...."

                  Comment


                  • #10
                    Part numbers change on the crankshaft up to 2001.-----Simply due to different seal arrangement for the splines.-----Time for you to study the parts diagrams to make them work.

                    Comment


                    • #11
                      Just cause you see crosshatch doesn't make bore true. I myself wouldnt run Siezecos as they require extra bore clearance and several heat cycles to toughen up. Cooling system has to be top notch to run em. I would punch it.040 and run WSM cast pistons.JMO
                      When in doubt,Trim it out!!!
                      Business Owner & Certifed Technician
                      Boats I own & use
                      20ft Javlin w/250 Junkrude
                      17ft Bullet w/200 Merc (SOLD!!)
                      13ft Allison w/150 I-6
                      17ft Hydra-Sport 175GT
                      15ft Allison w/75 Stinger(project)
                      14 x 48 Drifter with 1100SS Merc

                      Comment


                      • #12
                        Originally posted by ZandoR View Post
                        So would every crankshaft from 89 up fit my engine?

                        As I'm planning on ordering parts next week im still not sure whether to use a much cheaper WSM kit or buy Wiseco pistons and buy the bearings and gaskets separately. I wonder how much benefit there would be from the forged pistons.

                        Would it also be acceptable to buy just one new Wiseco piston and reuse the other two (skirts look great, just some carbon buildup on the top) if the bores check out okay? Do I comprimise reliabilty here?
                        Your crankshaft Part number is 334665. This is usually inscribed like a hologram (hard to see) in a circular form on the tapered portion of the crankshaft. Check for it.... always!

                        If the two remaining cylinder walls and the other two pistons look okay, clean and re-use the pistons. Make sure that the piston ring locating pins in the piston grooves are as they should be. A slight honing of the cylinders may be needed to restore the cross hatching.

                        Wiseco pistons are okay... I've used them many times. Just follow the break-in instructions.

                        My books only go up to 1992 due to retirement... so any possible interchange above 1992 is up to others.

                        The crankshaft has the same part number (interchangeable) - 1989 thru 1992 - 60hp, 65hp, 70hp

                        BJ70TLEND

                        B - Made in Belgium
                        J - Johnson
                        70 - Horsepower
                        T - PTT equipped
                        L - Long shaft (20")
                        E - Nine (9)
                        N - Two (2) - - - EN -92 (1992)
                        D - Factory run number, of no consequence
                        Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

                        Comment


                        • #13
                          Crankshaft up to 2001 will fit !-----Just need to pay attention to the sealing parts / pieces for the splines.

                          Comment


                          • #14
                            Now that's a lot of input! Thanks guys

                            Salvage yard: Unfortunately we dont have them here in Germany, so I have to go private seller.

                            Regarding the bore I will get it mike'd asap to see if I need to go .040 over.
                            Just a few shops that do these blocks here, they let you pay for it bigtime, so hopefully
                            it checks out okay. Will get you updated on the results.

                            So with the sealing parts, does it mean I would just have to watch out which seals to buy?

                            The plan is to do put it all back together in February when the semester has ended, so I'm trying
                            to have everything ready by then.

                            Again thanks for all the usefull information and for basically doing my research :P

                            Leo

                            Comment


                            • #15
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                              It seems that I might have gotten lucky with the crankshaft. Just need to check for the splines, but I'm positive.
                              Will send some pics when I have it.
                              Now theres the question about the bores. I inspected them once more, and found three spots that worry me a bit.
                              There is one small groove that catches my fingernail (top of the stroke), and another one that catches really slightly(around the port area).
                              Also the cylinder wall looks a bit different on the bottom of the stroke on most of the cylinder, no real scuffing though.
                              I wonder if this could be from to tight running Wisecos?

                              Something else I noticed is a piece of casting missing on the top cylinder, the sleeve is fine. Will I be fine with fixing it with JB weld?

                              Machine shop would charge me 60 Euros just to measure for out of round, and its about 250 Euros for reboring to 0.40 over.
                              So the question is whether to take the gamble of "wasting" the 60 Euros.

                              Would you guys sleep well over just using the bores as is after a hone? (In case the cylinder is true)
                              Attached Files

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