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Valve Lash Adjustment

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  • Valve Lash Adjustment

    With the recent addition of our Little Bird Forum, it is only fitting we have one for their Y-Block engines.

    All Y-blocks use solid lifters (and so do the early FE's), which need periodic adjustment. Valve lash adjustment is usually done as part of the tune-up procedure.

    There are many procedures for doing a lash adjustment, some employ special tools, feeler gauges, etc. Mechanics have done these for over fifty years. I won't pretend my method is 'better than yours', but please read it over for terrific insight that makes a very precision adjustment possible without buying any special tools.

    In a perfect world, rocker arms are smooth and straight, but after many miles the mating surface in the valve train become dimpled. This is normal wear as it 'cups' the valve stem. A feeler gauge cannot get inside the 'cup' for an accurate measurement.

    Look at the side of your rocker arm for casting numbers and determine which ratio you have.
    1.54:1 rockers are marked: ECG 6564-B2 or B1.
    Rockers without suffixes will be 1.43 ratio (so are #5751066).

    The tappet adjust screw has 20 threads per inch. One turn represents 1/20th of an inch or 050" of linear travel. Multiply .050 times your existing rocker ratio.

    HIGH RATIO ROCKER ARMS (1.54:1) <--most Thunderbirds
    Example, .050" (one turn) X 1.54(rocker arm ratio) = .077".
    Again, one full turn of the adjustment screw used in a 1.54 ratio rocker will represent .077" of tappet clearance.

    Now, divide one turn of tappet clearance i.e, .077" by 60 (as in the 60 minuets of a clock dial). This number is .001283" or 1 minute of clock face rotation. So, 15 minutes of rotation (which is 90*) will = .0192 Very close to .019" which is the specification for valve tappet clearance on 292 and 312 engines.

    *(Again, 15 minutes clock rotation = 90 degrees rotation; a scale easily understood and a super-close estimate to .019".)

    Let's use it: With the lifter all the down (on the cam's base circle) obtain some tappet clearance then carefully rotate the adjust screw clockwise to obtain .000" valve lash, just touching but not depressing the valve. (Roll the pushrod in your fingers to feel zero pressure.)

    Now rotate the adjust screw counterclockwise 90 degrees. The resulting clearance should be super-close to .019" regardless of rocker arm face wear.

    If you have lower ratio rocker arms, you can still use this procedure.

    LOW RATIO ROCKER ARMS (1.43:1) <--most Ford Cars
    Adjusting 1.43:1 ratio rockers:
    .050"(or 1/20") x 1.43 (arm ratio) = .0715" / 60(min) = .0011916 x 16(min) = .0190656"
    Rotate the adjust screw 16 min. of rotation ccw. To obtain .01906" clearance. Again, this is super-accurate.

    I hope this procedure helps everyone understand what's really going on and how to help adjust your lash. I do this when the engine is warm. - Dave Dare
    Last edited by simplyconnected; June 13th, 2020, 04:23 PM. Reason: Edited to correct punctuation and spelling.
    My latest project:
    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan

  • #2
    Great post and a tried and proven method!!

    Don't forget to do this at least every 10,000 miles!

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    • #3
      Valve tappet clearance is the same on exhaust and admission?

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      • #4
        Originally posted by Eric S View Post
        Valve tappet clearance is the same on exhaust and admission?
        Intake and exhaust lash is the same.

        My latest project:
        CLICK HERE to see my custom hydraulic roller 390 FE build.

        "We've got to pause and ask ourselves: How much clean air do we need?"
        --Lee Iacocca

        From: Royal Oak, Michigan

        Comment

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