Forums GPI Camshafts LT1 (Gen 5) Camshaft DI Fuel Pump clatter

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    I have a clatter when there is back pressure on the valve train. When gently accelerated to 2-3000 rpm and then barely back off the gas pedal. I also hear it on shifts.
    Not at idle, or on hard acceleration.
    Sounds like a rod knock, only in the valve train, like a rocker with too much lash.
    With cam lobe at high lift, I can tighten the pump bolts all the way down without the gasket, so no bind.
    With cam lobe at low lift, I can see .035 of clearance between pump base and valley cover, so plenty of preload. there should be no excessive lash.
    Is it possible the roller lifter is not holding its lash adjustment, I assume this is a big hydraulic lifter with internal check valve and leak down clearance.
    The pin holding the lash caps has .040 of movement in and out of lifter body. normal?
    Weapon X sells a heavier spring, but have not been able to get any information on why they developed it.

    WEAPON-X: High Pressure Fuel Pump Spring [Camaro Corvette CTS V, LT1 LT4 LT5]

    Considering changing lifter and fuel pump?

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