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How Do I Find The TDC Spot?

Discussion in 'Technical Q&A' started by donaldh2o, Dec 18, 2003.

  1. donaldh2o

    donaldh2o Karting

    Nov 10, 2003
    143
    Irvine CA
    Full Name:
    Don
    While tuning my 308, I'm almost sure the I've installed the distributor on the 1-4 bank 180' off. The car is running rough.

    I understand the distributors are to be installed with the flywheel at 7' (1-4) and 7' (5-8) and rotor caps pointing at the index marks on the distributors, making sure that #1 and #5 pistons are at TDC of their compression strokes.

    But how do I find TDC/compression stroke? Is this like trying to find the G spot (which I never could find)?

    One method I know is to rotate the engine CW while at the same time your finger is plugging the #1 spark plug hole - when you feel a little puff of air, you are nearing TDC/compression then finish by cranking to the 7' mark on the flywheel.

    But the spark plug hole is recessed and no part of my body is long enough to reach it. I tried everything. And that's on the #1 cylinder. On #5, you have to be two places at the same time: at the front, cranking the engine and, at the rear, testing for #5 compression.

    Geez, I think I just answered my own question: take an old spark plug, drill a whole down the center, install it, and attach a rubber hose to the top. There must be an easier way.
     
  2. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,157
    Texas
    Full Name:
    Steve Magnusson
    You might also be able to take off the engine oil filler cap and get enough of a look at the #1 intake cam lobe to figure out where you are. Rotate the crankshaft such that the #1 intake valve is fully open (i.e., the high point of the #1 intake cam lobe is pushing the shim/bucket down the maximum amount), then continue to rotate the crankshaft ~3/4 of a revolution (in the normal direction of rotation) to the next occurence of the #1 TDC mark -- that should be the end of the compression stroke for cyl #1.
     
  3. nautique

    nautique Rookie

    Nov 1, 2003
    20
    Los angelas, CA
    Full Name:
    Craig Tempelton
    Screw a compresion tester into the #1 plug hole. Then you can watch for movement of the needle on the gauge
     
  4. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,056
    San Carlos, CA
    Full Name:
    Mitchell Le
    I installed my dizzy with the following steps;

    1. Rotate flywheel to TDC 1-4 mark (you have them, right?)
    2. Install dizzy 1 making sure that the rotor points to the location of the 1 wire. Afterwards, turn the dizzy to the most retard position, and leave it
    3. Rotate flywheel 90 degrees to TDC 5-8
    4. Install dizzy 2 making sure that the rotor points to the location of the 5 wire. Afterwards, turn the dizzy to the most retard position, and leave it

    Static time it by

    1. Set flywheel to 7 degrees off TDC number 1-4.
    2. pull out the #1 wire, set it almost touching grd, and slowly advance the distributor by hand, stop when the wire sparks, lock it down.
    3. repeat 1-2 for 5-8 dizzy

    To find top dead center, I have a long rod that i stick down the cylinder with the plug removed, turn the engine until it rises to the top, and stops.
     

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