Installing a pull starter, need some help on what to do (pics included)

Discussion in '2-Stroke Engines' started by powerstroke, May 16, 2014.

  1. powerstroke

    powerstroke Member


    Click pics to enlarge.


    I need to fit the pull starter piece onto here, but that nut you see is in the way. See the picture below


    Thats as far in as it will go until it makes contact with the nut. I am reluctant to remove the nut because the thing its holding in place looks to be made up of many layers and I am afraid if it all came apart I would not get it back together.

    Has anyone done this before and know what to do?

  2. Fabian

    Fabian Well-Known Member

    The nut needs to be removed, then reinstalled after the pawl mechanism has been installed.
    Please be aware that the crankshaft threads on the magneto side are not very strong. It's terribly easy to strip the threads if you apply too much force, hence a good solution is to use Loctite 243 on the threads; then tighten the nut in place without excessive fastening torque.
    If you strip the threads on the crankshaft, you will have to replace the crankshaft; meaning that the whole engine needs to come apart. Please be very careful when tightening up the nut on the magneto side of the crankshaft; especially when installing a pull-start.
    If you f*&k this process up, it is the most costly f*&kup you can do on one of these engines, because a newbie is guaranteed to damage just about every part of the engine in the disassembly process; meaning that you will be better off buying a complete new engine; should you strip the threads on the magneto side of the crankshaft.

    It is important to note that there is a small amount of play between the shaft and the internal diameter of the magnet bore. When removing the nut, it pays to make sure that the magnet to magneto coil arm air gap is correctly set. This is explained in the second web link.

    This links might be of help. Give the web page load the photos:
    Last edited: May 18, 2014
    powerstroke likes this.
  3. powerstroke

    powerstroke Member

    Thanks for your information! I will pick up some loctite 243 today and when I do the bolt up I'll make sure to very lightly secure it.
  4. Fabian

    Fabian Well-Known Member

    It's not so much that it needs to be lightly secured, but more correctly said that it needs to be done up as tight as can be safely done with the amount of threads that you have available for the nut to grab onto.

    Every engine is different, but all of my engines have had the nut only hanging on by three quarters of the threads available on the nut, so it didn't give all of the available thread length to spread the fastening torque onto the pawl disk.
    You just need to be very careful, and need to have some experience as to how much fastening torque you can put on the nut.

    This is also a situation you need to be aware of:

    Last edited by a moderator: Dec 15, 2015
  5. powerstroke

    powerstroke Member

    Problem - When I twist the nut to loosen it the whole crankshaft (obviously) goes with it, I have tried sitting on the bike in gear to make it still so i can undo it but its not good enough the back wheel wants to spin with it still. How do I lock the crankshaft in place to get this nut off?
  6. crassius

    crassius Well-Known Member

    4.5mm allen wrench sitting in the drive chain will hold it
  7. powerstroke

    powerstroke Member

    The magnet still turns with the bolt even when the chain is locked with the allen key. Still cant get it off.
  8. Fabian

    Fabian Well-Known Member

    The magnet should "NOT" turn when the nut is unscrewed from the crankshaft. If it does, then the woodruff key has not been installed.

    I remove the nut and reinstall the nut using a butterfly rattle gun. Be aware that it is terribly easy for a newbie to make horrendous f*&kups when using power tools.
    I you accidentally press the wrong part of the butterfly wings, you'll strip the nut in an instant. Secondly, the better quality butterfly rattle guns have reasonably accurate torque adjustment settings, so you can set the gun to apply only a limited amount of fastening torque; giving some insurance against stripping the nut on the magneto side of the crankshaft.

    A butterfly rattle gun deletes the need to stick objects between the chain and sprocket teeth to lock up system.
  9. powerstroke

    powerstroke Member

    Misunderstanding here, I mean when I turn the nut the magnet and crankshaft turn with it, even when I've jammed the chain. I cant get this nut unscrewed.
  10. Fabian

    Fabian Well-Known Member

    You need to get yourself a butterfly rattle gun. This method allows you to undo things without having to stick objects between the chain and sprocket.
  11. powerstroke

    powerstroke Member

    Ok. I will try bunnings tomorrow.

    Also, what is the woodruff key?
  12. Fabian

    Fabian Well-Known Member

    Most of the time, the woodruff key will stick to the back face of the magnet when removing the magnet from the crankshaft.
    To install the pull-start, you 'do not' need to remove the magnet, but you are well advised to make sure the air gap is correct when tightening up the nut; which will now hold the pawl disk to the magnet.