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TDC 'Compression' stroke???

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by rodgonzbea, Jul 24, 2011.

  1. Hi..
    The machine is an 85 Yamaha SRX250, single cylinder.

    Replaced the shims, part of a long saga trying to restart the bike.

    anyhow, you know how sometimes you make those dumb ass mistakes that hopefully you'll only do once?? I did one.

    Took the camshafts off without marking them.](*,)](*,)

    Now, I have a manual, and there are instructions on reassembling.. How do I know its the compression stroke??


     

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  2. there should be a marker that shows up in an inspection window. the TDC for adjusting valves is where the marker lines up right in the middle of the hole, and you can feel a bit of play in the valves, don't quote me on this but this should be the same for what you're doing, possibly not. if there's no play then rotate the crank again until the marker lines up again and this should be the correct TDC. if you still can't feel any play then your valves are way too tight and you will have to find someone way smarter than me to figure out where the correct TDC is lol.
     
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  3. im thnkng mayb i complicated myself.. Compression stroke just means piston up.. Right? I thought it was related to a particular stage in the 4 stroke process.. As in compressing th fuel step.. Is that stage exactly what that window in th crankcase is showing?
     
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  4. Kernel is correct. Take the "points" cover off and TDC is where the marks align. You'll find that the ignition fires twice during the 720 degree rotation of the crank, so the camshaft determines which of the two up strokes it is on.

    The camshaft sprocket should also have a mark and the sprocket will be keyed to the shaft if it isn't cast in.
     
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  5. It's TDC on compression when both the valves are closed. The other TDC will have the exhaust closing and the inlet opening, so they'll probably both be a little bit open. Rock it a few degrees either way and watch the valves. If they don't move, then you're on the right TDC.
     
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  6. holy crap I was actually correct about something mechanically technical for once
     
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  7. ^This.
     
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