Old bolted crank

Discussion in '2-Stroke Engines' started by wagel, Aug 4, 2016.

  1. wagel

    wagel New Member

    Hi guys.. Just found out that one of the engines that I bought barely used and have not started myself has the old crank with bolted weights. Is it any good balance wise or should I just get a new solid block and balance that before putting the engine back together. Took it apart to change bearings.
     

  2. crassius

    crassius Well-Known Member

    those old bone-shaker motors were all we had for many years - they can be run OK, but will have a lot of vibration above about 25mph - they're good, serviceable, transportation if one keeps the speed down - run too fast, they tend to rip out the main bearings
     
  3. wagel

    wagel New Member

    Thats crap. Planned to tune it quite a bit. Anyway. Another totally unrelated question. The roofs of the transfer ports are tilted. I mean the transfer opens few mm earlier on intake side than exhaust. First jug I see with those ports. Does that give any benefit or should i just rise the port on exhaust side to have flat top? Otherwise its quite nice. Directed towards intake and so on.
     
  4. crassius

    crassius Well-Known Member

    transfer ports are on the sides, not front & back - the old H2 motors always had one transfer port a couple millimeters higher than other, which I guessed was to create a swirl effect to make mixture more uniform in chamber

    personally, I would leave it alone
     
  5. FurryOnTheInside

    FurryOnTheInside Active Member

    Reread the post. ;) ;) ;)

    I quite like the idea.. Not that I actually know whether it would work but it seems a cool idea to try. I would guess it does (or was intended to do) the same thing as directing the ports towards the intake side, clearing out the exhaust gases and losing as little of the fresh charge as possible.
    Now I want one too!
    Edit: oh, it turns out I have one. I thought it sounded familiar haha! :D
    Mine is rough as **** though and nasty deep scratches on the cylinder wall, I'll be ordering a new one off eBay when I get around to it.
     
    Last edited: Aug 4, 2016
  6. crassius

    crassius Well-Known Member

    reread it - guessing you have trapezoidal ports which are a bit taller at back than at front
     
    FurryOnTheInside likes this.
  7. wagel

    wagel New Member

    Yes. You got it right the second time. But any ideas is should I leave it stock or make it "normal".
     
  8. wagel

    wagel New Member

    Anyway. About the crank balance. Connecting rod has Z - L markings on it. Piston with rings and wrist pin clips is 80g, bearing is 5g and wrist pin is 14g. Didn't have tools to take the crank apart and weigh that so I didn't have all data for Jaguars calculator. Has anyone got data for this crank model so I could get it close enough? I might be able to drill the wrist pin and get some grams off there and piston is totally stock so I might be able to make it a bit lighter.
     
  9. crassius

    crassius Well-Known Member

    the trapezoid shape is supposed to be an improvement - I'd leave it alone - no data on crank
     
  10. FurryOnTheInside

    FurryOnTheInside Active Member

    I didn't even realise that it wasn't normal to have trapezoidal transfer ports. I have not split the cases on my engine but as far as I can see it looks like one piece solid type crank flywheels, I can't see any bolted on weights.
    But the method we discussed for drilling balancing holes without splitting the cases (drilling into the outside edge, after sealing the crankcase with putty etc) should allow a trial and error approach. You can drill a bit and see if it helps, drill a bit deeper and see if it helps more, etc..
     
  11. wagel

    wagel New Member

    Sounds like an idea. I guess I have to put the engine together as it is first to get some kind of reference point. Actually found a place where I could use a small hand operated hydraulic press which is meant for pressing car wheel bearings and stuff like that. But I'm not sure I will be able to put the crankshaft back together so that it stays "true". The bike is just a fun project and not a means of transport for me as it is totally illegal to ride it on the street anyway without registration which is not gonna be possible using a bicycle frame etc.
     
  12. FurryOnTheInside

    FurryOnTheInside Active Member

    We have the same legal problems here in UK which is why I am going for the Sick Bike Parts Shift Kit with their right hand side chain tensioner, and I should be able to disconnect and disable the engine entirely and unquestionably, without the need for tools, and in about five seconds, so I can use the bicycle as a bicycle when im out in public. :) but I'm off topic...
     
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