How To Check And Adjust The Valve Clearances In A Car Engine

Why You Need To Always Check And Adjust The Valve Clearances In A Car Engine

In order to save money and better performance in a car, it is important that the valve clearance is correct. Manufacturers do recommend checking the valve clearance regularly after every 5,000 to 6,000 miles. Checking valve clearance is a very important approach in ensuring that the engine efficiency remains at its optimum level. It is as important as checking the oil level in a car engine.

THE LOCATIONS OF THE VALVES IN A CAR ENGINE

The two valves located at the top of every cylinder head in a car engine play important roles in the engine combustion operations, without the valves being functional a lot of irregularities may become part of the engine operations, at its worst stage; a valve problem may cause the engine to become “unable” to start even when every other part of the engine are in perfect condition.

Valve clearance is the clearance created on the valve that allows it to be moved in and out of the cylinder head to allow air or fuel to flow into the combustion chamber. The action is usually made possible through the camshaft located above the sets of valves.

The use of valve springs enables the valves to return back to their proper position after being pushed ‘IN’ the cylinder head during engine operation. The extent to which the valve is pushed into the cylinder head for air or fuel entrance or for exhaust gas escape depends on the clearance provided in the valves during the engine manufacturing.

Hence, valve clearance impacts heavily on the overall engine performance and its efficiency in fuel consumption.
Some engines have hydraulic tappets which automatically provide the correct setting and these do not need checking. Some engines need special tools for checking their valve clearance such engines’ valve clearance may only be checked by a specialist in a garage.

BEST TIME FOR VALVE CLEARANCE ADJUSTMENT

There is two required temperature that the valve clearance should be adjusted. The adjustment can either be done while the car engine is still hot or when the arc engine has gone cold.

Car engine manufacturers always specify the best temperature suitable for the valve clearance adjustment in the car handbook manual or workshop practical manual.

When it comes to deciding an engine temperature that could be said to be ‘cold’, it is the temperature of a cold engine that has stood idly overnight.

While the temperature referred to as ‘hot’ is the engine at normal operating temperature, which is easily measured after the car has been driven for about four miles or more.

However, despite the commonly used extreme opposite temperatures some manufacturers use to specify the actual temperature their engine must be before any adjustment could be made to its valve clearances such car brands can be handed over to professionals for their valve-checking and clearance adjustment.

HOW TO MAKE VALVE ADJUSTMENT

The direct-acting overhead camshaft system is the easiest to check but can be the hardest to adjust because on some engines, the camshaft must come out and the bucket tappets lifted so that adjusting shims can be fitted underneath and such action will require a major dismantling job.

To reduce expenses, manufacturers of the car engines may specify a minimum valve clearance such that the vehicle owner will have the responsibility of ensuring the valve’s clearances do not go lower beyond the minimum rate specified in the engine manual.

Provided the valve gaps (clearances) do not go below the specified minimum figure, the engine will still operate satisfactorily. On most other valve mechanisms, adjustment of the clearances is made by turning an adjusting screw or nut and is straightforward.

Many engines have different clearance figures separate for both inlet valves and the exhaust valves. While all the valves seem alike in appearance when viewed from the stem end, they can be distinguished by tracing the line of the two manifolds.

The inlet manifold branches will aim at the inlet valves, and the branches of the exhaust manifold will point towards the exhaust valves.

Because each valve clearance must be checked with the valve in the fully closed position, it will be necessary to turn the engine to check them all. On in-line engines, it is possible to ‘pair’ the valves and save a lot of engines turning. For a four-cylinder engine, the ‘rule of nine’ can be used.

Number the valves from the generator end.
Turn the engine until one vale is fully open.

Subtract its number from nine, and the answer is the valve to check. For example, when you open valve number 2, it should become 9-2=7, so valve number 7 is the valve to check.
The principle mentioned above can still be applied to a six-cylinder car engine in a single line using the ‘rule of 13’ method. In this method, the crankshaft can be turned by using a spanner on the crankshaft pulley nut.

To use the feeler gauge for valve clearance adjustment check if the clearances are incorrect, on some car engines, it is only a matter of turning an adjusting screw to put each one right.

The clearance is correct when a clean feeler will slide into the gap with only moderate end pressure. If the gauge is a loose fit, the gap is too wide. But if the blade buckles are under pressure, then the gap is too small.

To use the method of Pushrod and Rocker, the valve clearance is checked between the tip of the valve stem and the rocker pad, with the engine hot or cold as recommended and with the valve fully closed.

As the camshaft is out of sight inside the block, you must calculate when the cam lobe is pointing directly away from the tappet and the tappet is resting on the cam wheel.

This is done by turning the crankshaft until the valve to be adjusted is fully open, and then turning it again in one complete revolution.

This will rotate the camshaft a half turn, putting the tappet on the heel of the cam lobe. It helps to put a chalk mark on the crankshaft pulley to show when it has rotated one revolution.

STEPS TO CHECK AND ADJUST THE VALVE CLEARANCES IN A CAR ENGINE

Follow these steps:

1. Identify the inlet and exhaust valves.
2.  Turn the engine using the rule nine or thirteen, until the valve is fully closed.
3. Insert the appropriate feeler gauge into the gap. It should slide in under moderate pressure. If it is too loose or too tight move to the next step.
4. Where the rocker has an adjuster on one end, loosen the lock-nut, and turn the adjusting screw clockwise to reduce the clearance, or anti-clockwise to increase it. Some engines have purpose-made stiff adjusting screws which do not have a lock nut.
5. Some pushrod engines have the adjusting nut at the center of the rocker, and the valve clearances are set with the engine at the normal operating temperature and running. Do not use an ordinary feeler gauge for this rather use the long feeler strips for that purpose.
6. Run the engine at idling speed. Put a socket or box spanner on the adjusting nut. Insert the feeler blade between the moving rocker pad and valve stem. If the gap is too small, the feeler will be difficult to fit and the engine will run unevenly when it is in position. If the blade rattles, the gap is too wide.
7. Adjust the nut until the engine runs smoothly and any feeler blade rattle disappears. If you find it difficult, stop the engine and check the gap statically.

HOW TO CARRY OUT VALVE CLEARANCES IN A CAR ENGINE ON AN OVERHEAD CAMSHAFT USING SHIMS

Below is a step-by-step approach on how to carry out valve clearances in a car engine that has an overhead camshaft arrangement using shims.

1. Refer to the handbook manual to know if the checking of the valve clearance will be done when the engine is at its cold temperature or at its hot temperature.
2. Remove the camshaft cover on the top of the engine. The action will require you to disconnect the high-tension cables at the spark plugs, note that you must mark the high-tension cables once you disconnect them to ensure you recognize the actual plug that connects with each cable after the whole operation. The action will also require disconnecting the fuel pipe at the carburetor and removing the air cleaner from the carburetor.
3. Turn the crankshaft until one cam lobe is pointing directly away from the tappet.
4. Check the manifolds to ascertain whether the valve is for inlet or exhaust, then use a feeler gauge to check the clearance between the tappet and the heel of the cam lobe. Make a note of the valve and make a note of the clearance.
5. Turn the engine until the next cam lobe is pointing directly away from the tappet and repeat step 4. Continue this procedure until all the valve clearances have been checked and noted.
6. Compare the clearances with the manufacturer’s recommendation. On a single-carburetor for instance, some manufacturers may state that no adjustment is necessary until the valve clearances are less than 0.012in (i.e. 0.30mm).
7. If clearances do need adjustment and you are not clear on how to go about it, take the car to a professional to do it for you to avoid damaging any vital part of the car engine in the process, thereby introducing an unexpected expense.

Conclusion

The above details clearly made lots of coverage on engine valves and valve clearances in a car engine. However, feel free to give feedback through the comment section.