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    2007 Pontiac Grand Prix 3.8L SFI OHV 6cyl

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    1720 S RIDGEWOOD A
    (386) 427-1210

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    Cam Shaft

    Inspect/Test/Service/Replace

    Camshaft Lift

    Using a Micrometer

    • The camshaft lobe lift can be measured using an outside micrometer.
    • Lift is determined by measuring the lobe from heel to nose, and subtracting the base circle measurement from it.
    Determining camshaft lobe lift. Reprinted with the permission of Ford Motor Company.
    • Camshafts with high durations cannot be measured using a micrometer, since a true base circle measurement will not be obtainable.
    • This is due to the ramps beginning more toward the heel.
    • In these instances, use a dial indicator to measure the lift of the pushrod.

    Using a Dial Indicator

    • Another method is to install the camshaft onto v-blocks and use a dial indicator to measure the amount of lift.
      • Locate the plunger of the indicator on the heel of the lobe and zero the indicator.
      • Rotate the camshaft until the highest reading is observed.
      • This is the amount of lobe lift.
      • Check camshaft straightness before checking lift in this manner.
    • Another method of measuring lobe lift involves installing the camshaft into the engine block with the lifters and pushrods.
      • A special cup-shaped adapter is installed onto the dial indicator to accept the pushrod.
      Use a special adapter to measure camshaft lobe with the camshaft installed in the engine. Courtesy of General Motors Corporation.
      • With the pushrod at its lowest point of travel, zero the dial indicator.
      • Continue to rotate the camshaft until the maximum amount of deflection of the dial is observed.
      • This represents the total lift of the camshaft.

    Camshaft Journals

    Measure the camshaft journals for size, taper, and out-of-round using an outside micrometer.

    Worn camshaft journals can cause the valve timing to change as the engine is running. Courtesy of General Motors Corporation.
    • To determine the amount of out-of-round, measure each journal in two different directions and compare to specifications.
    • Also check for journal taper by measuring at each end of the journal.
    Compare each journal to specifications and check for taper. Courtesy of Chrysler Corporation.

    Camshaft Straightness

    • Camshaft straightness can be checked by placing it in V-blocks.
    • The camshaft is supported in the blocks by the journals on both ends.
    • Install a dial indicator onto the central journal.
    Measuring camshaft warpage. Courtesy of Honda Motorn Company.
    • Observe the dial indicator as the camshaft is rotated.
    • A TIR (total indicated reading) of 0.002 in. (0.050 mm) indicates excessive warpage.

    Base Circle Runout

    With the camshaft set up to measure straightness, also check base circle run-out.

    • Locate the dial indicator plunger on the heel of the lobe and zero the gauge.
    • Slowly rotate the camshaft until the lowest gauge reading is obtained. This is the point where the camshaft lobe ramp starts.
    • Note this reading, then rotate the camshaft in the opposite direction until the gauge indicates the start of the other ramp.
    • As a rule, total run-out should not exceed 0.001 in. (0.025 mm).
    • If the run-out is excessive, the lifters may pump up when the valve is closed.
    WARNING
    If it is determined the camshaft requires replacement, always replace the lifters. The camshaft and lifters become wear mated within a short time, and used lifters will rapidly wear a new camshaft. It is possible to replace a single lifter without replacing the camshaft.

    Camshaft Construction Material

    One method of determining the material used is a spark test.

    • Although this test will not give exact indications of the alloys used, it is a good guide.
    • This test uses a high-speed, medium-grit grinding wheel.
    • When a noncritical area of the camshaft comes into contact with the wheel, sparks will be emitted.
    • The pattern and color of the sparks will indicate the type of material.

    Camshaft End Play

    • Install a dial indicator to measure the lateral movement of the camshaft.
    • Then use a screwdriver to gently pry the camshaft back and forth.
    • The TIR of the indicator is the amount of end play.
    • Some engines use shims to correct end play.
    • If shims cannot be used, the camshaft may be faulty.

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