How To Adjust Valve Clearances For Engines With Camshaft & Fingers Arrangement And To Check The Externally-Adjusted OHC Clearances
Some car engines have finger or follower interposed between the valve and the camshaft lobe. The engines with such arrangement the clearance can be checked between the heel of the cam and the finger.
The steps to be used in carrying out adjustment or checking of the valve clearance are easier if the steps were properly understood. Below are the steps to follow for such task:
- Identify the inlet and exhaust valves.
- Check the gap using a feeler gauge.
- If the clearance needs altering, loosen the lock-nut, and turn the stud anti-clockwise to close the gap, clockwise to close the gap, clockwise to enlarge it.
- After that, couple the engine back the way it was before carrying out the operation.
Ford engines use the camshaft and finger arrangement on its single overhead camshaft engines. With such type of engines, you might find it difficult in some cases to turn a lock-nut near the carburetor. Most garages make use of special crowsfoot spanner to get over this problem, but the lock-nut can be turned with an ordinary spanner if the carburetor is removed.
How To Check The Externally-Adjusted OHC Clearances
To overcome the problem of dismantling the camshaft and tappets to make valve adjustments, some manufacturers such as Fiat and Vauxhall and others provide an easier method of adjustment.
When working on the Fiat OHC engines, the adjusting shims are recessed in the top face of the tappet. If a clearance is correct, a special tool is used to lever the tappet away from the camshaft, the old shim will be removed and a new one of the correct thickness is inserted in the place of the old one.
When working on Vauxhall OHC engines, no shims or special tools are needed. This means that the adjustment is a straightforward job. The gap is altered by a small transverse Allen screw in the tappet, with a ramp on one side.
The steps below show how the gap can be adjusted:
- Identify the inlet and exhaust valves.
- Check the clearance on each one with the cam lobe pointing away from the tappet.
- To alter the clearance, rotate the tappet until a niche appears. The access hole for the screw lies below the niche and aligns with a cut-out in the head casting.
- Use a small Allen key to turn the screw one full turn at a time, anti-clockwise to increase the gap, or clockwise to decrease it. Each complete revolution of the screw alters the gap by 0.003in i.e. 0.008mm.
- After adjustment, re-check the gap with a feeler gauge.
