If the camshaft and crankshaft drive gears require replacement, this can be done with the engine in the car. Manufacturers of engines with pressed-fit camshaft gears make special tools that can be used to hold the cam forward during gear installation.
If the cam sprocket is the nylon type and chunks of gear teeth are missing, the oil pan must be removed in order to extract teeth from the oil pump screen and oil pan.Failure to do this will result in oil pump failure later when the pieces get sucked into the pump and block oil flow.
This oil pump sprocket is filled with the teeth of a nylon timing sprocket that failed.
Replacing A Camshaft Gear
When replacing a pressed-fit camshaft gear, use a puller to remove it from the cam.
- Disconnect the negative battery cable.
- Remove the covers protecting the camshaft drive gears.
- Check for proper alignment of the timing marks on the timing gears.
- Remove the timing gears according to the service manual.
- Clean the timing gears.
- Inspect the gears for wear or cracks, and replace necessary parts.
- After replacing any worn or damaged gears and drives, set the timing marks according to the service manual.
- Rotate the engine through two complete rotations of the crankshaft. Check to see if the timing marks on the gears are still in proper alignment.
- Reinstall all covers removed for access.
- Reconnect the negative battery cable and start the engine.
- Set the ignition timing to the manufacturer's specifications.
Installing A Camshaft Gear
When reinstalling the gear, take care that the cam does not move to the rear; it could knock loose the core plug in the rear of the block or chip cam lobes on neighboring lifters.
- The rear of the cam gear must be supported while the cam is pressed from its center.
- After the new cam gear is pressed on, end play is checked with a feeler gauge.
Checking the clearance behind the thrust plate to determine camshaft end play. Courtesy of Federal Motors Corporation, Service Technology Group.
- The clearance between a cam thrust plate and the sprocket or gear varies from 0.0015" to 0.005".
- If a spacer is used, it must be from 0.0015" to 0.005" thicker than the thrust plate.
- The cam will press against the spacer, which fits inside the thrust plate hole, controlling end thrust.
- In some cases, adjustment is made by replacing the thrust plate.
- Some engines limit the end play of the camshaft through the use of a cam button.
- A nylon button or torrington bearing sets on a spring and is installed between the camshaft timing gear and the timing chain cover.
- Aluminum gears can be heated for easier installation.
Do not forget the spacer on a cam with a bolt-on sprocket. The result could be a cam that will not turn after the bolt is tightened.