Motor starter has probs after rebuilding engine
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Motor starter has probs after rebuilding engine

This is a discussion on Motor starter has probs after rebuilding engine within the Technical forums, part of the Caferacer.net Forums category; Hi all! I got a Suzuki gs450L 1987 I had to take my cilinder off to do some work. When putting it back together I ...

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Thread: Motor starter has probs after rebuilding engine

  1. #1
    Junior Member daansteegmans's Avatar
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    Hi all!


    I got a Suzuki gs450L 1987

    I had to take my cilinder off to do some work. When putting it back together I put the timing bolt on RT and checked if the right cilinder was on top. I put my valves cams back on with the #1 aligned horizontally with the head. Put the valve chain back on. Counted 18 steps, starting from #2 to the other cog wheel’s #3 marker. Everything was put back together but when I try to run the engine it has problems running the pistons up and down. It feels like it has way to much resitance and I could feel my wires getting hot. When I remove the sparks it goes smoother.

    Any ideas on what I did wrong?

    Cheers,
    Daan
    Last edited by daansteegmans; 09-25-2019 at 01:38 PM.

  2. #2
    Senior Member TrialsRider's Avatar
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    Trying to understand this :/ so is the resistance you are concerned over engine compression ? and the compression goes away when you remove the spark plugs? because yes that makes perfect sense.

    Wires getting hot :/ you lost me there, Plug wires or other? ... I can't say I've ever grabbed a spark plug wire to see how hot it is, with my luck I'd get a heck of a good shock.

    Now lets assume you have put the engine back together and the valve timing is close enough that you are not crashing the pistons into the valves. If I wanted to know if everything was functioning like a 4-stroke motor should, I would do a compression test and for that you don't even need to start the motor, just turn it over a few strokes.

    Hope that helps some, how far off am I from understanding the problem?

  3. #3
    Junior Member daansteegmans's Avatar
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    Thanks for the reply TrialsRider!

    So I dont know much about engines..

    I'll try to clear it up a bit:
    with the spark plugs IN, and trying to electric start the engine, the pistons only go up and down once every second or so (which seems way to slow to me?).
    When doing this for let's say 6s I could see one small black wire giving a little fume of smoke, like almost melting. Thats when I felt the rest of the 'wiring bundles' and they were all getting pretty warm.
    When removing the spark plugs the pistons go up and down faster. Not sure if that means anything :/

    If you say to test the compression I could turn the engine over a few strokes, how do I know the compression is ok?

    Is it perhaps possible that there is an electrical problem or wouldn't the starter engine even run in that case?

    Thanks a lot!

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  5. #4
    Senior Member TrialsRider's Avatar
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    Ok, electrical wiring getting smoking hot is not a good thing, you have a short circuit somewhere and for some reason your fuse did not blow. That is scary.

    A 4 stroke motor is just like a big air compressor, to do a compression test you remove a spark plug, bung a dial gauge compression tester into the plug hole and turn the engine over. The compression tester has a dial gauge that tell you how many pounds per square inch of compression your engine is producing on its compression stroke ... probably in the vicinity of ~180 pounds.
    (or whatever your service manual says) if your valves are not right your compression will not be right so right away you would know you have a problem.

    In a 4-stoke motor your crankshaft (pistons) go up and down at twice the rate of your cam shaft.

    As for how fast does the starter need to turn the motor over to start it? <- idle speed. If you can't spin the motor up to idle speed it probably won't start.
    Last edited by TrialsRider; 09-25-2019 at 05:12 PM.

  6. #5
    Senior Member TrialsRider's Avatar
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    If you had the head off you need to adjust your valve clearances and you can't do that until your cam timing is correct, valve clearance is set at TDC (Top Dead Centre) which is the correct term to describe when the piston is at the top of its travel.

    For compression TDC your intake valves have just completed closing and the piston is on its way up to TDC. Just a couple degrees before that your spark plug fires the fuel/air mixture.
    Don't accidentally set your valve clearances on the next TDC stroke, which is right after the exhaust valves closes and the intake valve starts to open.
    ... is a 4-stroke motor so the crank turns over twice for each time it goes bang, it is the compression stroke TDC where you set the valve clearance not the one following that.
    Last edited by TrialsRider; 09-25-2019 at 05:14 PM.

  7. #6
    Junior Member daansteegmans's Avatar
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    I checked this tutorial to set the timing right:

    When I align the #1 marker arrow with the cilinder head, the left cilinder cam lobe is already pushing one valve down, which makes the cam shaft not just fall in its place. That's not supposed to be like that right?
    Last edited by daansteegmans; 09-26-2019 at 03:26 AM.

  8. #7
    Senior Member TrialsRider's Avatar
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    The marks for the cylinder you are setting the timing by would logically indicate TDC, at TDC none of the valves on that cylinder should be open, so ya it sounds like your valve timing is not right.
    Just be careful you don't set it so the valves collide with a piston :/ that would be devastating.

    ... must confess I did not watch the video yet, I usually just go by the service manual. Do you have a copy of the OEM service manual?

  9. #8
    Junior Member daansteegmans's Avatar
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    I do not have a service manual unfortunately but on all the videos I've seen they explain it exactly the same but it seems like it doesn't match with my cam shafts for some reason

    So maybe this explains it better: (screenshot from video above)
    Here he can align #1 on the cam shaft with the top of the head but when i do that i have to really push the cam shaft down in its place because one of the cam lobe (X on screenshot) is already facing downwards, or is that supposed to be like that?

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    Last edited by daansteegmans; 09-26-2019 at 08:38 AM.

  10. #9
    Senior Member TrialsRider's Avatar
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    Not sure I can get my head around it without seeing it :I need to relate the position of the cam lobes with the start of the power stroke on each cylinder,
    at #1 TDC, the #2 cylinder is at BDC. Either it has just completed the intake stroke and the intake valve has now completely closed,
    or just finished a power stoke and the the exhaust valve is just starting to open to open, because we know the crank shaft is staggered 180 degrees, correct?
    So if my brain can think in 2 cylinders all your valves are now closed, I think something is wrong, when #1 is at TDC #2 should have both valves closed.
    Would be real nice if somebody could proof read that for me!

    ... no way you could have mixed up the intake and exhaust cams or cam parts is there, or is that impossible ?

  11. #10
    Junior Member daansteegmans's Avatar
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    I'll just have another fresh look at it this weekend and see if I missed or mixed up anything..
    Thanks for your help TrialsRider!
    TrialsRider likes this.

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