GMC 12703806 Camshaft Assembly, Overhead Vlv

Remove the intake manifold, rocker arms, pushrods, timing chain, camshaft sprocket, along with the fan shrouds, water pump, radiator, and A/C condenser.

Slowly turn the crankshaft clockwise until the indicator needle stops and moves in the opposite direction, noting the maximum cam lobe lift.

Yes, good used roller lifters can be reinstalled with a new camshaft.

The measurement for cam lobe lift should be taken by slowly turning the engine until the pushrod is at its lowest point (base circle of the camshaft lobe), then zeroing the dial indicator. The crankshaft is then rotated in the normal direction until the indicator needle reaches its peak and begins moving in the opposite direction, marking maximum cam lobe lift. This measurement is important to assess camshaft wear.

Before installing the camshaft, you should lubricate the camshaft bearing journals and lobes with assembly lube.

To assess cam lobe wear, check the lobe lift before removing the camshaft by first removing the valve covers and positioning the number one piston at TDC on the compression stroke.

Alternatively, measure the camshaft lobe height and base circle with a micrometer after removal to determine lobe lift.

Clean the camshaft with solvent and dry it.

To check for a noisy valve lifter, you can use a mechanics stethoscope or a length of hose near each valve while listening for excessive clearance in the valvetrain. If a lifter is defective, it will be evident from the noise.

Proper labeling and storage of the lifters are essential to ensure that they are returned to their original locations during reinstallation, preventing any mix-up.

If the lobes are in good condition and the measurements are as specified, the camshaft can be reused.

The initial steps to remove the camshaft are disconnecting the cable from the negative battery terminal and relieving the fuel system pressure.

After installing the camshaft, the cooling system should be refilled, the oil should be changed, and a new oil filter should be installed before starting and running the engine.

The steps to remove the camshaft are as follows:1. Remove the intake manifold.2. Remove the rocker arms.3. Remove the pushrods.4. Remove the timing chain.5. Remove the camshaft sprocket.6. Remove the balance shaft drive gear.7. Remove the fan, radiator, and condenser.8. Store the lifters in a labeled box.9. Remove the lifter retainer.10. Extract the lifters from the bores using a special tool, magnet, or your fingers.11. Remove the camshaft retainer plate.12. Use three 6-inch long, 5/16-18 bolts as a handle to remove the camshaft from the block.

It is recommended to replace both the camshaft and lifters together, especially for high-mileage engines.

After installing the camshaft, proceed to install the balance shaft drive gear, aligning the dowel pin and ensuring proper alignment of the balance shaft timing marks. Then, install the timing chain and sprockets.

The steps for installing the camshaft are as follows:1. Lubricate the camshaft bearing journals and cam lobes with assembly lube.2. Slide the camshaft into the engine.3. Install the camshaft thrust plate.4. Install the balance shaft drive gear.5. Install the timing chain and sprockets.6. Lubricate the lifters with clean engine oil.7. Install the lifters in the block.8. Complete the installation in reverse order of removal.