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  • SR timing chain

    Long story short, SR head gasket job was done by a shop to a friend's customer's motor. job was botched and can ran like crap. only thing done was a HG so i suspected mechanical timing was off.

    we pull the valve cover and see the cam timing marks are between links on the chain, aka half a link off compared to the factory. the oil pump wasn't touched so we are pretty sure the crank sprocket should be on a link, not in between. the number of rollers in between the marks is correct (20). We move the chain to what we think is the right direction, but it's always hard to view it (aka 10'oclock vs. 10:05 for example) without being able to count links down to the crank sprocket. so few questions here:

    1) why does the ESSAR not have a reference mark between the 2 cam sprockets or an extra reference mark up top on the block?
    2) can the timing chain move from the crank sprocket when the oil pump is on? we checked a spare oil pump and saw there are dowels which prevent the chain from dropping when the cams are removed, so it leads me to think the chain can't jump timing at the bottom unless you pull the pump.

    So we guessed at the mechanical timing to the approximate pictured locations in the FSM, but all we know for a fact what's correct is the 20 rollers between the cam gear marks, not any of the roller lengths going down to the hidden crank sprocket. fire up the car and in order to set the ignition timing light to match the power fc's live ignition timing readout, we need to advance the CAS all the way. this tells me mechanical timing is still off, and we need to move the chain again - but which way?

    3) which way do i need to rotate the cam sprockets? my guess is both gears should be moved one full link CCW.

  • #2
    Chain cannot fall off the crank sprocket. you are correct.

    Put car at TDC align the #1 cyl cams as shown in FSM and you should be good to go.

    this is all I, or anyone I know of directly, have ever done before,

    If you need to after setting valve timing, reset the CAS alignment (just like a Dizzy) if there is a thicker HG i have sometimes found the CAS to be at the edge of it's range to get proper base timing
    I am SKULLWORKS

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    • #3
      thanks ok that is reassuring about the chain staying on the crank sprocket.

      good point about the CAS. I completely forgot it isn't keyed and needs to be aligned. I'm sure it is off a bit because we never pulled it back to reset the alignment after advancing the ex cam sprocket. i'll give that a try and hopefully it'll be somewhere close to the middle of its adjustment when i base time the ignition. i was pretty sure we had the chain set right, but was doubting myself cuz the CAS needed to be maxed so far.

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      • #4
        2) can the timing chain move from the crank sprocket when the oil pump is on? we checked a spare oil pump and saw there are dowels which prevent the chain from dropping when the cams are removed, so it leads me to think the chain can't jump timing at the bottom unless you pull the pump.
        While it can't 'jump ship' it can bind and crack if a hack shop is doing the work. I've pulled engines apart to discover the broken lower 'keeper' for the chain. Because of that I may put extra emphasis on keeping the chain 'up' and utilizing a chain block.

        3) which way do i need to rotate the cam sprockets? my guess is both gears should be moved one full link CCW.
        With cars that have had mechanical timing off/don't want to pull front cover, I just pout the engine to TDC via timing marks on teh crank pulley, and then just align the cams per FSM...as well as counting the links between the dots, as well as counting links between edge of head and each mark

        You can also use this quick guide from Enthalpy:
        http://rs-enthalpy.com/tuning/sr-cam-alignment.doc
        'Slicks on a car show me you care - broken axles show me you're trying'
        [I]Nitrous Rental Cars - Turbo Festivas - Vehicular Lunacy[/I]
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