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Thread: timing question

  1. #16
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    Indexing the flywheel rotation only hides the problem and does nothing to fix it unless you use piston position to index it. It must be timed off of the cylinder with the most advance or better yet find the problem and correct it. Pay attention to Jay he knows what he is talkin about.
    Last edited by lpugh; 10-29-2009 at 11:31 PM.

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    is any one taking into account the fact that piston movement has freeplay due to berring clearences at the crank, piston pin ect... wich will account for atleast a degree across the assembly in a broke in motor.. the fly wheel mark really needs to be indexed by rotation.. as you will get dwell in the piston at TDC for a couple degrees, check all your electronics yes.. but also varify your light, and your indexing marks on all 6 cylinders... your timing may be closer than you actually can show due to grind angles ect as well.. just something to think about as well..

    4-16-2014. 25 years old today... the fishin boat doesnt look to bad for a classic does she


    things that were are no longer as they are today...

  3. #18
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    I just posted about a stator issue I might be having and it has some similarities with what your seeing.

    What if... the stator was out of phase and the caps were charging late.

    Wouldn't this also make the timing whacky. If the trigger fired the switch and the cap was still in the process of charging the coils would be firing late and the timing would be all over the place. I think mine is either 90 or 180 out, yours may just be off by 1 screw hole.

    Mines got me baffled, I'm going to try and move the stator one screw hole at a time and see what happens. I've got new CDI switchboxes being overnighted to me also.

  4. #19
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    timing

    i didn't touch it yesterday. probably play around with it today. i've indexed the flywheel once making marks on the flywheel and to double check myself i used tape around it and re-indexed it to make sure i wasn't screwing something up which i'm prone to do. if this were a 150hp fishing motor then i could just bring the high number down to 25 and run it but i would rather not do that on this motor. i talked on the phone yesterday to a mercury mechanic that also is an experienced drag racer and he strongly suggested switchboxes so thats where i'll start. next will be the trigger and flywheel. thanks for the suggestions guys, keep em coming
    Erik Kiser

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    indexing

    so you guys are saying to do it with a degree wheel instead of a dial indicator in the spark plug hole. seems to me that we're trying to achieve ignition at .150" BTDC and that can be determined by using a dial indicator in each cylinder. i understand dwell time and all that and took it into consideration when indexing each cylinder on the flywheel.
    Erik Kiser

  6. #21
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    After sifting through all this information the motor still has to be timed with a light in conjuction with a static pointer on the block and a flywheel that has had the rotation indexed off the piston.. Indexing the flywheel with a drgree wheel without taking the piston TDC and a reverse.150" mark into consideration does NOTHING to show whats happening when the motor is in RUN mode... Folk can try to re invent the wheel but the "problem" WILL be solved when the electrical issue is found. Trigger, switch box , or firing magnets on the flywheel ring is the only 3 things that makes this prosess happen...Then and only then will this thing be brought closer to correct timing on all holes...

    BTW: I curious how would one set a degree wheel atop a flywheel and begin indexing if a piston at TDC is not a starting point ????

    my .02
    Jay
    Jay @ JSRE


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    timing

    your right lightnbug. i was trying to determine the likely cause for the difference.
    Erik Kiser

  8. #23
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    I've built a few motors and all lately I index the flywheel going clock wise first off the piston top with a JSRE TDC indicator on all 6 piston tops then rotate counter clock wise at .150" off TDC counter clock wise just as Erik did to establish 25* if I find the variance to be unacceptable on one side lower or higher in an equal proportion I reverse the switch box and if the problem follows the suspect switch box I've found the problem, if the values are random from starboard to port I look for a trigger issue...Has worked for me for years.

    Maybe I've just been lucky,

    Jay
    Jay @ JSRE


  9. #24
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    I should have already known this...
    Using a flywheel marked by degrees will show if the ignition is firing accurately.
    If the ignition fires properly on a degreed wheel and not using the dial indicator method then the problem is mechanical and not electrical.
    I don't think finding TDC even matters when using the degree wheel method as all it does is determine if the ignition fires at the proper intervals......
    This could be a useful tool but I will still use Jay's dial indicator to set timing....
    Last edited by Scott in MN; 10-30-2009 at 08:47 AM.

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    Again just curious Scott and all involved , how would one alter a mechanical ISSUE ???? And would that "mechanical" issue be bearing slop or a slightly bent crank... I can understand a slightly bent crank "could" () be fixed , but what could or would one do to remove the inhierant slop of a needle bearing motor con rod bearing ???

    I'm trying to learn here....
    Jay
    Jay @ JSRE


  11. #26
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    Jay, in thinking on this I would much rather have the problem be electrical in nature. As much a pain it is chasing electrical gremlins a mechanical issue would be even more time involved. I would think replacing mechanical parts is also the only way to fix a mechanical issue. If all parts are straight and have the same clearances the motor should not have any mechanical timing issues, right? I just think that the degree method is another tool for troubleshooting.

    Scott

  12. #27
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    In thinking even further, bearing slop if it is equal on all cylinders will not effect the outcome of your dial indicator tool as long as a person is consistent in using it (ie. taking the readings as you come up the cylinder on each one and not by going by and reversing to the reading).

  13. #28
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    TDC has dwell. That's why Mercury gives the .464 to set the pointer.
    By using a degree wheel you are setting the timing marks for each cylinder exactly 60* apart. Now when you check each cylinder you will see exactly where the timing falls. If the ignition fires at 60* of rotation each time you know the ignition is correct. It has no bearing where the piston is. If the timing fires erratically then you know it is an ignition problem. As Lightnbug said it is a way to differentiate between a mechanical and an electrical problem.


    Some engines do fire a little off of exactly 60*, it may be #2 is slightly more advanced than the others so do your timing to #2, the most advanced cylinder, and you won't have a problem due to advanced timing on a cylinder.

    A piston can be mechanically off due to machining errors, twisted crank, main bearing slop, etc.
    Never argue with an idiot. They drag you down to their level, then beat you with experience.

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  14. #29
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    I haven't ever checked a Merc crank, but have seen some production
    Chevy and Ford cranks that are way off.

  15. #30
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    Figure in the fudge in the placement of the trigger magnets in the hub as well as all the other factors.

    I had a gnarly on the edge 2.4 that was giving me fits. It finally came down to indexing the flywheel and having to base max timing off of #5, (+4* ahead of other cylinders) The crank was weird on a run out check and replaced with another, picking up a significant amount of rpm up top and ending the curse of the piston eating beast.

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