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Establishing actual TDC...

Discussion in 'Technical Q&A' started by fastradio, Sep 14, 2009.

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  1. fastradio

    fastradio F1 Rookie
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    Apr 26, 2006
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    New England
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    David Feinberg
    #26 fastradio, Jun 13, 2011
    Not exactly. What they are stating is that if the cam opening point is not correct, you can back up the engine by rotating it backwards until the valve is starting to open, then lock that cam in place...remove the locking pin and then rotate the engine in the direction of travel until the degree wheel reads correctly. At that point, you will reinsert the pin in the corresponding hole. If you're fortunate, a hole will line up. If not, the pulley will need to be removed and realign so a matching hole can be found.

    In the same breath, if the cam timing is off the other way (degree wheel indicates correct opening point), the engine will not be rotated, but rather the cam will be rotated to achieve the correct opening point. The pin will still need to be removed and to play it safe, the cam (on the same bank) that you're not adjust should be locked in place.


    This is a given and not Ferrari-specific. Regardless of engine type, the tensioner should always be locked before opposite rotation is done.
     
  2. mwr4440

    mwr4440 Five Time F1 World Champ
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    Jun 8, 2007
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    Mark W.R.
    #27 mwr4440, Jun 14, 2011
    I am just beginning this process.

    To use a Piston Stop on a 2V motor you have to remove the cams ..... RIGHT?


    But to use a "Pole and Dial" type method like in FBB's thread you do not?



    Is this correct? I am lost. :eek:
     
  3. davehelms

    davehelms F1 Rookie

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    Dave Helms
    #28 davehelms, Jun 14, 2011
    ...and one heck of a lot faster. This is the method I use as there is no chance of dinging a piston top, fouling an opening valve.... I dont like things that go Clunk. I can get two readings on either side of TDC and have 4 measurements to calulate from with only small amount of crankshaft rotation. Most Ferrari applications show 1mm piston drop to be quite close to 12.25 degrees before and after TDC with the piston dwell taken into account. When an angled spark plug head design is encountered the piston stop method is then the only reliable way with an assembled engine.
     
  4. Mark 328

    Mark 328 Formula Junior

    Nov 6, 2003
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    Mark Foley
    #29 Mark 328, Jun 14, 2011
    Mark:
    I have read about it, but have used the dial indicator method on my car. The error with the dial indicator method is in not being able to remove the backlash. What that means is on one direction (say 10 Deg Before TDC) you are “pushing” the piston up on the other side (say 10 ATDC) the piston is being “pushed” down. There is some backlash.
    How the piston stop guys do it is with the old belts and then they are pushing-up on both sides. I think this is the most accurate method for a hemi engine. Side plug engines should probably use the indicator method.
    Ideally, you would find TDC with the cams-out; but with the old belts in is second best; it is not a good idea to rotate backwards with the new belts.

    Mark
     
  5. dino clay

    dino clay Karting

    Oct 31, 2007
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    san mateo, cal
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    clay cavanaugh
    #30 dino clay, Jun 15, 2011
    after scanning some of these replies:

    NO, do not rotate engine back to find tdc, you face the DANGER of taking the back lash out of the chains. Not going to waste both of our time by explaining further.

    Use dial indicator.

    Bring engine to tdc and set indi. to zero
    Rotate engine 360 degrees and stop at some given figure before tdc, say 0.030"
    read dgrees on dgree wheel, say 20 dgrees btdc
    rotate engine past tdc to 0.030" after tdc
    degree wheel should be split evenly, should read the same dgrees before tdc as after top tdc

    If not. loosen dgree wheel and adjust so that wheel reads the same dgree onn either side of tdc

    recheck that adjustment of dgree wheel measures the same, now you are at absolute tdc and have eliminated all chain variations, piston rockover and a whole lot of other errors

    by the way it's spelled degree

    clay
     
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