GMC 12703806 Camshaft Assembly, Overhead Vlv

Use bolts threaded into the camshaft sprocket bolt holes to pull the camshaft out of the block, supporting it to prevent damage to the bearings.

Inspect the balance shaft and measure the bearing journal diameters; if measurements exceed specifications, replace the balance shaft, bearing, and bushing as a set.

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

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.

To determine the extent of cam lobe wear, position the number one piston at TDC on the compression stroke, remove the valve cover, and loosen the rocker arm nuts to access the pushrods. Then, mount a dial indicator on the engine, position the plunger against the top of the first pushrod, and zero the dial indicator. Slowly turn the crankshaft in the normal direction of rotation until the indicator needle stops and moves in the opposite direction, indicating maximum cam lobe lift. Record this figure and repeat the check for each valve.

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.

The initial steps for checking camshaft lobe lift before removal involve removing the valve covers and loosening the rocker arm nuts to pivot the rocker arms for access to the pushrods. A dial indicator should be mounted on the engine, positioned directly above the first pushrod.