fitting and setting a vernier pulley

Discussion in '8-valve' started by alexisblades99, Mar 12, 2010.

  1. alexisblades99 Forum Member

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    i've finally got round to doing this over the last couple of days, so i thought i'd put up a few pics if anyone's interested.

    spec of my engine is a 2l bottom end, man in the shed solid lifter counterflow head with a kent gs2 cam to improve breathing over the standard item. higher lift opens the valves wider, and for longer, than the original camshaft.

    setting the cam timing alters the point at which the valves open in the engine's cycle, and changes the behaviour of the engine. i use my car as a daily driver, so i need the power to be available in the midrange of rpm rather than high up in the rev range.

    piper vernier pulley:

    [​IMG]

    finding top dead centre precisely is important. the piston doesn't move much around TDC as it 'dwells' for a few degrees, so to determine exactly where it is i made a pointer:

    [​IMG]

    which i screwed into the PAS pump bracket so it points at the crankshaft pulley:

    [​IMG]

    and one of these:

    [​IMG]

    out of an old spark plug with the electrode smashed out, and a piece of threaded bar. the threaded bar can be screwed in and out and locked in position to provide a stop for the piston:

    [​IMG]

    removing the spark plugs allows the engine to be turned easily, this tool is screwed into no.1 spark plug hole, and the crankshaft turned (gently) until the piston contacts the tool. the crank pulley is then marked at the pointer, then the engine turned the opposite direction until it contacts again. mark the pulley, then TDC is exactly half way between the two marks:

    [​IMG]

    i tried finding TDC by using the dial gauge with a probe down the spark plug hole:

    [​IMG]

    but it was a lot more time-consuming, and no more accurate. also the probe would skitter across the surface of the piston as it rose and fell and didn't really inspire confidence.

    interestingly the crank pulley mark was pretty much spot on:

    [​IMG]

    but it's possible it can be a few degrees out so this isn't always the case. i then marked TDC on the flywheel end for future reference.

    i decided to check the existing timing. with engine set to TDC, firing stroke no.1 cylinder. dial gauge mounted over no.4 cylinder so i could compare inlet valve lift to the kent cams recommendations. turned the engine back a bit to zero the gauge with the valve fully shut:

    [​IMG]

    then wound it forward to TDC and found the inlet valve lift at TDC to be 2mm higher than the kent cams setting:

    [​IMG]

    they recommend 1.88mm of inlet valve lift at TDC on overlap, this was 3.93mm, so clearly too advanced. there was a bit of confusion when i first fitted it as to whether i should line up the standard pulley mark with the rocker cover or with the top of the head. this was lined up with the top of the head, but if it had been lined up with the top of the rocker cover it would have been within half a tooth of bang on:

    [​IMG]

    next up removed the standard pulley, and fitted the new one. a dab of loctite on the woodruff key just to make sure:

    [​IMG]

    cambelt refitted, engine set to TDC and the inlet valve lift checked, a little retarded so slackened off the adjusting bolts and turned the camshaft until it showed the correct valve lift:

    [​IMG]

    and that's basically it. further tweaks can be made easily by slackening off the adjuster bolts and moving the cam timing with the pulley scale as a reference.

    edit: Apparently it's the timing of the inlet valve that's the most influence on where the power is. I'm still a little fuzzy about how changing the cam timing affects the engine's power curve, but I think I got it wrong before, so apologies. As said by other wiser people, advancing will move the powerband down the rev range. I think this is due to the trapping efficiencly of the inlet stroke. Could someone who knows fill me in on how this works?
     
    Last edited: Aug 11, 2010
  2. 3hirty8ight Forum Member

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    Great write up.. STICKY?
     
  3. 8vDUB Forum Member

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    exallent. what cam have you got?
    i thought advancing the cam moves the powerband down?

    good write up.


    neil
     
  4. 8vDUB Forum Member

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    and how did you know how long to make the stop?
    and how far is your cam advaced on the pully now.
    if thats 30 degrees each way i didnt realise a degree was so little. mine doesant have them marks
     
  5. alexisblades99 Forum Member

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    cam is a kent gs2, not overly wild, just over 10mm of lift.
     
    Last edited: Aug 11, 2010
  6. pigbladder Forum Addict

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  7. alexisblades99 Forum Member

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    no worries, glad it's of some use. :thumbup:
     
  8. i.a.n.b Forum Junkie

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    Intresting read, this is on my list of things to get done.
     
  9. Blue MK2 Forum Member

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    Thanks mate. Good info. Is advancing a case of moving it clockwise yes?
     
  10. ozdub New Member

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    Hello,

    I have my pulley fully adjusted (retarded) is it possible also to re adjust my dizzy aswell or would this not have an affect in moving the timing ie getting more from it? just wanted to check before i played with it all. 2.0 8v agg.
     
  11. alexisblades99 Forum Member

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    as far as i know, running the cam retarded (more exhaust lift than inlet lift at TDC) won't gain any power over neutral timing, and may make you more likely to experience exhaust gas reversion. that's where not only is there exhaust gas left in the cylinder at the end of the exhaust stroke, but it gets sucked back in as the inlet stroke begins.

    that would lead to reduced power, and higher temperatures, which in turn could limit the amount of ignition advance you could run without suffering from pre-ignition. i'd set the cam to equal lift on overlap and maybe advance it from there if you like.

    as far as ignition timing goes, you'll lose power by running it retarded from the optimal setting, so try advancing the ignition timing a degree at a time till the engine 'pinks' under load, then back it off a bit.
     
    Last edited: Mar 14, 2010
  12. alexisblades99 Forum Member

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    basically if i'd had a degree wheel handy, i would have mounted that on the crank pulley as it's easier than blobs of paint and probably a bit more accurate. the wider the angle between the marks, the more accurate the measurement, but with the stop being adjustable you can play with it to set it up correctly.

    cam is set to neutral timing (equal lift on overlap) so neither advanced nor retarded.
     
  13. 8vDUB Forum Member

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    thanks for that. so with your standard pulley set to the head, how far out was it from true.

    im guessing you said with the standard pulley it was not eqal, was the pulley lined with the head? how much did you need to advance it to make it exactly eqal.


    trying to sort mine but have no timing figures, and no dti for that matter.

    thanks
     
  14. 8vDUB Forum Member

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    is the picture of the orange dot on the standard pulley where it would have been eqal overlap with standard markings. so if you had lined it up to the head it would have been over a tooth advanced?

    just trying to get my head round this
     
  15. alexisblades99 Forum Member

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    that's it i think.

    [​IMG]

    the picture shows the cam set to equal lift, and the red dot is painted on the factory timing mark.

    as the red dot was lined up with the top of the head originally, that was giving me a tooth advanced from equal lift. if i'd lined it up with the top of the cam cover flange, as would be the case in this picture (if the cam cover was on), it would have been pretty close to equal lift.

    the adjustability of the vernier combined with the accurate measurement of the dti just allows you to get it bang on, as opposed to the nearest tooth.
     
    Last edited: Mar 14, 2010
  16. 8vDUB Forum Member

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    I just set eqal lift as close as i could. Had both on#1 pointing up and i could rotate both buckets. #4 both pointing down. Vernier adjusted to get the belt on and tensioned. I think im geting this. Thanks
     
  17. pre67 Forum Member

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    top thread loads or good info

    just a quick qustion what way would i want to go on mine as i have had 1mm scimed off my head to get the comp up

    would i want it more adv or ret just to bring it to the standed time to make up for the 1mm
     
  18. Jon Olds Forum Junkie

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    Very good thread.
    Be aware the std pulleys (especially the bottom one have 'slop' in them. They will bolt up in different positions Not clever when you do a cambelt (etc) change.
    Just about to install a new head onto an engine in the car myself. More lift , skimmed head etc,
    Jon
     
  19. alexisblades99 Forum Member

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    cheers :thumbup:

    you're right about the pulleys, there was a fair bit of movement there. i took the opportunity to mark the flywheel once i'd found tdc as it's an aftermarket item without any timing marks.

    @pre67 you'd have to advance it a touch. you're effectively shortening the belt by 1mm, so i think you'd need to advance the cam pulley by 1mm at it's circumference to get the teeth to line up.
     
    Last edited: Mar 14, 2010
  20. Mikey Forum Member

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    So would it be best to set the TDC mark on the flywheel (mine is a standard flywheel with marks on it) rather than the crank pulley because of this 'slop'?
    Been trying to get my head around timing recently as Ive replaced the dizzy on my 2e & need a timing belt changed soon too.
    Before removing the original dizzy I set the rotor arm to the notch mark on the edge of the dizzy, so assumed this was TDC. Checked the mark on the crank pulley & this didnt line up with the pointer on the belt cover, it was a few degrees towards the bulkhead. Forgot to check the dimple on the flywheel to see if this lined up (doh!)
    Since Ive fitted the new dizzy Ive had to retard it slightly from the original marks to stop pinking & to get the car running smoother. So does this show that the original dizzy was slightly off TDC & that I should have put a DTI on the piston to get the true TDC point? Or that if I should perhaps have set the flywheel dot to the gearabox pointer for a more accurate base point to work from than the original dizzy notch/rotor arm positions?
     

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