Most overhead valve engine have different size journals, with the largest being toward the front of the engine. This is done to make the camshaft removal and installation easier.
Removing OHC Camshafts
On overhead cam engines, the camshaft is removed with the cylinder head. Follow manufacturer's instructions for the removal of the cam from the head. This varies with the design of the head.
If the lifters on a pushrod engine are too worn to be reused, the following procedure will save time in removing the cam:
- With the engine in the upside down position, move the lifters to the highest positions in their bores by turning the crankshaft one complete revolution.
- Use a piece of wooden dowel to finish pushing the lifters into their bores so that they will clear the cam.
The lifters must be removed high enough to allow the cam to be removed. Courtesy of Dana Corp., Perfect Circle Division.
- Now the cam can be carefully removed. This is a delicate operation.
- Support the camshaft during removal to avoid dragging lobes over bearing surfaces, which would damage bearings and lobes.
- Do not bump cam lobe edges, which can cause chipping.
Removing Pushrod Camshafts
Some engines use a bolt-on cam thrust plate.
Some camshafts have a thrust plate to control end thrust. Courtesy of General Motors Corporation, Service Technology Group.
Gear-drive cam bolts can be accessed through holes in the cam gear to remove the cam.
- An impact screwdriver is sometimes necessary to remove Phillips head screws.
- Varnish often builds up on the edges of the cam journals, making it difficult to remove the cam. Squirt some penetrating oil on the varnish.
Varnish buildup on the edge of the cam journal makes camshaft removal difficult. Courtesy of Dana Corp., Perfect Circle Division.
- Unbolt the cam sprocket and slide or pry it off the cam.
- Then remove the chain.
- Reinstall the sprocket and tighten one bolt fingertight.
- Use it as a "handle" to remove the cam.
- It is easier to remove the camshaft without damaging the lobes if the engine is stood on end.
If the engine is mounted on an engine stand and the cam will not come out, try supporting the cam gear end of the block. Sometimes the block will sag just enough to bind the cam. This is especially true on inline six-cylinder engines.
Installing OHV (Overhead Valve) Camshafts
Install the camshaft into the block. Be careful to protect the journals and bearings. If the block is not installed on the engine stand, it can be rested upright (vertically) to make cam installation easier. Following is a guide to typical procedures for installing the camshaft into OHV engines.
To assist in the installation of the camshaft, install 4 inch bolts into the threaded holes at the front of the camshaft. Use the bolts to rotate the camshaft and to push it into the engine block.
- Determine oil clearance between the installed camshaft bearings and the camshaft journals and compare with specifications.
- Use a rag soaked in solvent to remove any coating on the camshaft journals. Be careful not to remove the coating on the lobes.
- Lubricate the journals with engine oil or assembly lube before fitting the camshaft into the block.
A special assembly lube is used on cam lobes. Courtesy of Dana Corp., Perfect Circle Division.
- Install the camshaft, preventing any contact between the lobes and the bearings.
- When the camshaft is fully seated in place, spin it to assure free rotation.
- Install the sprocket or gear and use it as a temporary handle to turn the cam during installation.
- If rotation is impaired because of high spots on the bearings, they can be removed using a three-corner scraper.
- Slight corrections to the bearings can be made with a flex hone.
- Make sure to clean the engine block after performing these operations.
- If the bearings are not the cause of the binding, the camshaft may be bent.
Do not use emery cloth to remove high spots. The grit can embed in the bearing surfaces and damage the journals.
Long in-line engines attached to an engine stand may flex enough to prevent free camshaft rotation. Try supporting the front of the engine also before condemning the camshaft or bearings.
- Apply sealer to the outer edge of the rear core plug and install the plug with the convex side out.
The camshaft plug is installed at the rear of the block. Courtesy of General Motors Corporation.
- Drive the plug to the specified depth.
- Once the core plug is installed, use a dull punch to deform it slightly. This increases the tension applied to the outer edges to provide a positive seal.
- After the core plug is installed, rotate the camshaft to be sure the plug is not causing interference.
- Install the camshaft retainer plate.
- Measure the camshaft end play and correct it if needed.
Checking camshaft end play. Reprinted with the permission of Ford Motor Company.
- Apply special camshaft break-in high-pressure lubricant onto the lobes, being careful not to get any onto the journals.
After Reassembling the Engine
It is especially important that the engine starts up immediately to avoid excessive loading between the cam lobes and the lifters.
- Start the engine and run it at 1,500 - 2,000 rpm for about 20 minutes to allow the cam and lifters to begin to wear to each other.
- Idling should be avoided during this period to prevent cam and lifter failure and because, during idle, less oil is thrown off the connecting rod journals onto the cylinder walls, cam, and other parts that need this critical lubrication.
- Make sure the engine has oil pressure.
- Watch the coolant temperature to see that it does not climb too high.
- Check for oil leaks.
- If any adjustments are needed the engine should be shut off immediately.
With the idle set high, a carburetor will probably have to be choked off to stop the engine from dieseling (running on).
- After the initial 20-minute period, the idle can be reset and the ignition timing can be checked with a timing light.