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Performing a top-end overhaul, camshaft replacement, or fuel timing calibration on a Cummins N14 or 855 Big Cam diesel engine? Follow this step-by-step professional workshop procedure to set up the M20070 dual dial indicator fixture, measure piston displacement, and set PT injector pushrod travel cleanly.

Why Loose Indicator Arms Cause Engine Misfires & Black Smoke

On mechanical Cummins PT diesel engines, the timing of the fuel injection stroke is controlled by the camshaft keyway position and cam follower pushrod setting. When setting up PT injector timing, technicians must measure the precise position of the piston near top dead center (TDC) while simultaneously measuring the downward stroke of the injector plunger follower. If a mechanic attempts to take these measurements using magnetic indicator stands clamped to valve covers or frame rails, movement in the stand introduces fatal measurement errors. A deflection of just 0.002″ (two thousandths of an inch) on the dial indicator changes injection timing by several crankshaft degrees. This error causes cylinder imbalance, high exhaust gas temperatures (EGTs), heavy soot accumulation in turbochargers, and poor fuel economy. Utilizing a dedicated, rigid alignment fixture like the 7-pound M20070 locks both dial indicator shafts squarely into the cylinder head deck. This guarantees a rock-solid, vibration-free reference plane—allowing mechanics to record true piston position and adjust timing shims or rocker screws to exact OEM specification.

The 5-Step Cummins PT Engine Timing Protocol

1. Safety & Cylinder Head Deck Preparation: Lock out the ignition and disable starter circuits. Remove the valve cover and rocker arm assembly for the target cylinder. Thoroughly clean carbon, oil scale, and debris off the cylinder head deck and injector bore landing.
2. Mount the M20070 Fixture Base: Secure the main M20070 fixture block squarely onto the cylinder head deck over the target cylinder. *CRITICAL: Ensure the fixture base bolts down flush and rigid against the head deck surface to eliminate flex.*
3. Install & Zero Piston & Injector Indicators: Insert the piston extension rod through the injector hole to rest against the piston crown. Mount the first dial indicator to track piston travel. Mount the second dial indicator over the pushrod follower. Bar the engine smoothly in direction of normal rotation until the piston indicator reaches absolute Top Dead Center (TDC), then zero the dial.
4. Bar Engine & Record Pushrod Travel: Bar the engine past TDC to the specified piston position value listed in the Cummins service manual (e.g., 0.090″ ATDC). Observe the reading on the injector pushrod dial indicator to determine exact injection stroke timing.
5. Adjust Camshaft Gear Shims or Rocker Screws: If the measured pushrod displacement does not match OEM spec, adjust the camshaft gear keying/shims or rocker arm adjustment screw as required per engine model guidelines. Re-bar the engine through two full revolutions and re-verify indicator values before removing the M20070 fixture.

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