connecting rod bearing is shot

Discussion in '2-Stroke Engines' started by Haggard, Nov 17, 2007.

  1. Haggard

    Haggard Guest

    Howdy fellas.
    got some slop in my connecting rod to crank bearing. up and down aswell as the usual side to side .
    having probs cracking the case. whats an easy way to remove the reduction gears and sprocket from other side to allow the casing halves to be seperated??
    ive got all the bolts and the nuts/washers off out but not sure how to remove the keyways so as to remove the actual gears / sprocket??!!!??? : (
    getting old and forgetful i guess,
    thanks in advance
    ~Haggard~
     

  2. srdavo

    srdavo Active Member

    did you get the funny lil gear puller with your kit? the tool is reversible & works on both reduction gears & the engine sprocket.

    http://www.motoredbikes.com/showthread.php?t=4761&highlight=funny+tool

    Important step: pull out the metal dowel from the center of the shaft, where the engine sprocket is attached, before using the puller.
    there is also a ball bearing behind the dowel...watch for it.

    MY Question...after the gears, sprocket & magnet are removed,.....do the bearings need to be pressed out of the cases before splitting?
     
  3. Fabian

    Fabian Well-Known Member

    I am in the process of getting a series of bolts machined, designed specifically for pressing apart the crankcase halves.

    Having split two engines, with diabolical difficulty, and after getting the advise of a kart engine rebuilder, his opinion is that the press fit of the crankshaft bearings into the crankcase halves is far in excess of what it should be and also the press fit of the crankshaft bearings onto the crankshaft is far in excess of what it should be.
    He has never seen an engine with such a tight press fit on anything he has worked on - in his opinion, the press fit tension is completely wrong.

    His opinion is that the overly tight press fit into the crankcase halves is contributing a significant portion to the vibration experienced in these engines, aside from the woefully bad crankshaft balance factor.

    Splitting the cases will cause the crankshaft alignment to go out of true and pressing the cases together will also have the crankshaft running out of true, even if it has been trued prior to installing in the cases.

    The only way to fix the problem is to have the bearing reciever pockets remachined for the correct press fit tension and to use a machined crankshaft installation tool to maintain counterweight alignment as the halves are compressed together with screw tension.

    Fabian
     
  4. arceeguy

    arceeguy Active Member

    Fabian - did you notice that this thread is 2 years old? Just goes to show you how rare lower end bearing failures really are.

    I've never heard of a crank going out because of removal or installation in a crankcase. I do know that splitting a crank, pressing it back together and adjusting runout is something that most people can't do at home.

    Heating the aluminum case halves helps a lot with splitting them. The aluminum expands more than the steel bearings, and they'll come apart a lot easier.
     
    Last edited: Nov 1, 2009
  5. Fabian

    Fabian Well-Known Member

    Yes, it was a post from 2 years ago
    Is it a case of people not responding to the post or just that bearing failures are very rare.

    You want to come down to my neck of the woods to see the trail of big end bearing failures.

    Maybe i tend to be more vociferous than most.

    Just reading the threads, there are numerous posts on how to rebuild a Happy Time style engine.
    Those people will just be clamping the case halves together with screw tension.
    The result of the bearing reciever pockets being too tight a press fit will have the crankshaft halves placing excessive compression on the crankshaft pin, thereby closing up the crank halves and throwing the crankshaft out of true. Even if properly balanced, it will vibrate as it's not running true.

    These are not my words but from a respected kart engine builder.
    He has more experience than i have and has a reputation in the local karting scene of "getting it right".

    Even simpleton logic works when thinking about it.
     
Loading...