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Classic Honda 50's JZ Refurb

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  • Classic Honda 50's JZ Refurb

    I purchased my JZ in the early 90's for $1000.00 registered, it was my first regoed monkey bike, I wasn't looking for a regoed bike as I only wanted it to ride off road and race around the track with the boys from West Wallsend, rode it part of the way home which was pretty exciting with major death wobbles at 80 kmh and having to try and outrun and out manouvre all of the cars trying to get a look at me.

    The bike was too good to race offroad so I quickly found a Z50R to replace it, at the time there was no internet, forums or ride days and I didn't know anyone who rode a Z50 on the road, all my mates had big bore 2 & 4 strokes so I rode it around the local bush tracks on my own for a few years until I decided to strip the JZ for a quick cleanup, haha that was almost 20 years ago

    This is how the bike has sat for most of that time, I blasted the frame and swingarm with ilmenite and painted them with a gloss black acrylic, replaced the swingarm bushes and fitted Takegawa 280mm shocks:




    The fuel tank is is very good original condition but it will be resprayed with the fork legs to match the new plastic Honda OEM fenders:




    The engine had an 80's performance upgrade with a cleaned up Honda 70 head and cam, modified 51mm CB400 piston for 85cc, Honda 70 modified inlet manifold and carb that sat straight back, Honda SL70 4 speed gearbox and a stock exhaust, went pretty good at the time, the only strange thing was the J1 air filter, thought they must have needed it for the carb set-up:




    When I took the flywheel cover off something looked strange as it had a J1 flywheel, looked at the engine number for the first time that I remember and it was a Z50J1 JE engine not a JZ, well that was surprise number 1:




    Extremely clean inside the engine, note the indents in the philips head screw on the gear selector plate to hold it in place, has roller bearings on the non drive end of the main and counter shafts, thought that I would be seeing a brass bush woo woo surprise number 2:




    This is the old top end showing the modified CB 400/4 piston, not much meat left above the top ring, re-sleeved cylinder, cleaned up Honda 70 head and stock clutch, had a heap of fun with it:




    Surprise number 3 was how worn the countershaft was and also found a case bolt that was seized, drilled off the head and onto the next job, luckily I had parts of an old SL70 box that included a countershaft that was in very good condition :




    This is the oil gallery from the oil pump, it had quite a rough finish that I cleaned up with a dremel:




    Just needed to be cleaned it up a little:




    Honda SL70 4 speed gearbox, thankfully in fantastic condition, I gave this gearbox a real hard time on the track and out the bush for a few years then heard that they had a reputation of breaking easily, this one survived and never missed a beat except for the poor old countershaft:




    Rebuilt the gearbox with new clips, washers and bearings all round plus the replacement countershaft:




    Happy days with the cases de-burred, cleaned and semi polished and the engine rebuild end in sight:
    Last edited by Classic Honda 50's; 2nd March 2013, 05:08 PM.
    Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

    PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

  • #2
    Classic Honda 50's JZ Refurb

    I use new head studs on any performance build and always feel on the home stretch when I get to this point, then for surprise number 4 when the 52mm cylinder would not fit into the engine cases so close but now so far, been selling TB 52mm cylinders for almost 6 years and this was the first time that I have had a problem with a cylinder fitting, then a customer rings up a week later with the same problem, good mock up now it is time to pull it apart and enlarge the opening into the cases:




    Used the base gasket as a template and enlarged the cases with a dremel, come up quite good even if I do say so myself:




    Base race prep on the TB Parts roller rocker race head with the ports hand finished, inlet port matched to the intake manifold and valve guides honed:




    Polished combustion chamber and a 3 angle valve job with the Neway valve seat cutting kit:




    Top end in place with no more surprises, I like to glue the heat spacer in place so that it matches spot on with the intake port, leave it to firm up and then line up the intake manifold, keeps it lined up and the intake port matched every time:



























    Last edited by Classic Honda 50's; 2nd March 2013, 05:12 PM.
    Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

    PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

    Comment


    • #3
      Classic Honda 50's JZ Refurb

      3333333333
      Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

      PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

      Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

      Comment


      • #4
        Wow what is it.
        Need a new motor.

        Comment


        • #5
          Putting the pictures up now.
          Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

          PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

          Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

          Comment


          • #6
            tease ,,,!!!
            its engine oil madge ,,,
            Your soaking in it ,,!!

            Comment


            • #7
              Forum rules = pix!
              If you listen carefully you can hear rhubarb growing

              Comment


              • #8
                Looking good.........where do you get your new parts from?
                Once I thought I was wrong, I was mistaken

                Comment


                • #9
                  Nice 106 stroker. Looks like 6v.

                  Comment


                  • #10
                    Oh just realised you have pics up! .

                    Comment


                    • #11
                      I support Australia and get all of my parts through Classic Honda 50's Australia

                      More pix up with more to come, will add comments shortly, it is a 6v stroker motor babu.

                      Cheers

                      Jaimie
                      Last edited by Classic Honda 50's; 2nd March 2013, 11:43 AM.
                      Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

                      PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

                      Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

                      Comment


                      • #12
                        Would like to see how the points ignition system works through and beyond 10,00rpm. CDI For the win.
                        For Reproduction Monkey Bike - Wiring Harness', Key switch and ignition components, repairs and custom work - https://www.facebook.com/monkeypowerinc

                        Comment


                        • #13
                          looks awesome mate. wish that motor was in my white j1..
                          its not the size of the bike that matters its how ya ride it haha!

                          Comment


                          • #14
                            Nice write up Jaimie, looks good so far. Good to see you're putting that new valve seat cutting kit to good use !
                            Cheers,
                            Rod

                            Comment


                            • #15
                              Can't wait to get it on the dyno to see what it can do.

                              I would definately go for CDI if I was after maximum power but this motor will end up in my wife's J1 so hopefully 10000rpm won't be seen very often, it will be interesting to see when the points give up, points were king once upon a time.

                              The Neway seat cutting kit works a treat, takes a little practice to get the cutting pressure right, still have to get the 75 degree cutter so I can do 4 angle seats.

                              Have a few versions of the TB 108 stroker to dyno down the track to give people an idea how different set-ups compare:

                              1) 81 Z50JZ with 6v TB 108cc stroker TB roller rocker race head, Mikuni VM24 carb, stock points stator, stock coil, tuned length exhaust (Next on the dyno).

                              2) 97 Z50R with 12v TB 108cc stroker TB original race head, Mikuni VM24 carb, Takegawa Super Street Outer Rotor Ignition System, Takegawa Coil, Takegawa CDI, tuned length exhaust.

                              3) 03 XR50 with 12v TB 108cc stroker TB roller rocker race head, Mikuni VM26 carb, stock stator, stock coil, TB CDI, Fast 50s exhaust, currently an 88cc engine.

                              4) 76 Z50J1 with 6v TB 108cc stroker TB original race head, Shengwey 24mm carb, stock points stator, stock coil, tuned length exhaust.

                              Cheers

                              Jaimie
                              Classic Honda 50's Australia - Visit our online store at - www.classichonda50saustralia.com.au

                              PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

                              Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

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