[HELP] How To Open 4 strokes motor with distribution Chain

Discussion in 'Thumpers' started by CrustyD3mon, Apr 19, 2012.

  1. CrustyD3mon

    CrustyD3mon Been here awhile

    Joined:
    Jan 4, 2010
    Oddometer:
    284
    Guys,
    I need some help...i need repair my first bike...an AJP PR4 125cc from 2001...

    It's a 125cc with four stokes motor based on Honda Technology...

    Never need to open it for nothing...it's always put gas in it...and role the throttle!!

    But recently i have a problem with the second gear...and need to reach the gearbox to verify what it is...


    I take the motor from the frame...and i'm prepared to take the cilinder of...but first need to know...what i need to pray attention...

    The valves...the distribution chain...etc...its necessary mark some position before...for reference or something?

    Can anyone help..? I can post a pic of motor later if it's necessary...
    #1
  2. Peanuts

    Peanuts Long timer

    Joined:
    Sep 12, 2009
    Oddometer:
    2,005
    Location:
    Beautiful but often rainy North Yorkshire, UK
    There will be a mark on the flywheel when the piston is at top dead centre, set it like this and there should be maks on the cam that line up with something like the gasket surface.

    There are two top dead centres for each 4 stroke cycle, you need to set it at compression TDC such that the inlet and exhaust valves are fully closed when you take the motor apart.
    #2
  3. troidus

    troidus Long timer

    Joined:
    Sep 1, 2010
    Oddometer:
    45,170
    Location:
    Georgia
    A service manual will be your friend.

    I don't know your specific engine, but there should be a timing mark on one end of the crankshaft. There should also be timing marks on the cam sprockets. If the engine is still whole, rotate the crank until the crank timing mark points to top dead center and the cam marks point where they're supposed to, whether aligned with the edge of the cylinder head or to some other marking. A quick verification will be to look at the cam lobes for #1 cylinder and make sure they are not actuating any valves. Once the timing marks are aligned, count the number of timing chain pins between the timing marks on the cams and write that down. When you reinstall the chain, knowing the number of pins between the marks will help you get everything realigned.

    If you have screw adjusters for the tappets, loosen them completely so that if you do botch the cam timing, you won't bend any valves. After you turn the crank a couple of times by hand and make sure the timing marks are still aligned, then you can re-set the valve lash. If you have shim adjusters, just be careful when you dead-time the engine to keep from bending anything.

    Good luck.

    Edit: 205'd by Peanuts. I should type faster.
    #3
  4. CrustyD3mon

    CrustyD3mon Been here awhile

    Joined:
    Jan 4, 2010
    Oddometer:
    284
    #4
  5. troidus

    troidus Long timer

    Joined:
    Sep 1, 2010
    Oddometer:
    45,170
    Location:
    Georgia
    It's much simpler than I originally described. I saw 1255cc in your original post and assumed a DOHC inline-4. A 2-valve SOHC single is much easier. I think your crank timing mark is under the CDI cover on the right side. Under the small slotted cover on the left should be a means to turn the crank. Look there for a timing mark before pulling the right cover off. The cam timing mark I think is the round depression between the chain and the bolt head at the 9:00 position. What you're supposed to align it with is a mystery, but if the crank timing mark doesn't have a reference point or the point is straight up, I'd look for the cam mark to be pointed straight down. For the chain alignment, make sure you always rotate the crank in running direction to keep the chain in tension between the crank and cam, with the crank sprocket providing the tension. The chain tensioner is to take up the slack on the chain return to the head and can throw off your cam timing if you rotate the engine backwards before everything is in place. Your valve adjusters are screw-and-locknut, so you can back those all the way out to prevent bending a valve as you get your cam timing set.
    #5
  6. CrustyD3mon

    CrustyD3mon Been here awhile

    Joined:
    Jan 4, 2010
    Oddometer:
    284
    When you say "uder the CDI cover" are you talking about that cover:

    [​IMG]

    This is the cover of the cam that is off in the second picture....on the left side of the engine....the cam mark it's supposed to be in that cover?
    #6
  7. CrustyD3mon

    CrustyD3mon Been here awhile

    Joined:
    Jan 4, 2010
    Oddometer:
    284
    It's been a while since i started this thread...and due some professional reasons, this repair was in standby since the last post...

    I already open my motor, and ssems that i need some material..:p

    [​IMG]

    I already have almost everything...only waiting from one carriage...
    #7
  8. Stretch67

    Stretch67 Mad Scientist Supporter

    Joined:
    Mar 22, 2006
    Oddometer:
    20,201
    Location:
    Bent, But Not Broken
    Ouch!
    #8