JAKE ADJUSTMENT ON ISX

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It either has excessive valve recession, incorrect cam timing (check that someone hasn't fitted the vibration damper incorrectly while you're at it) or the rocker shafts have not been fitted correctly (could be due to poor head casting or incorrect steps taken while fitting the shafts).

Not being able to get the 7mm feeler between the jake lever and top hat is cause to remove the head and measure valve recession in Cummins warranty guidelines.