In order to save money and better performance in a , it is important that the is correct. Manufacturers do recommend checking the regularly after every 5,000 to 6,000 miles. Checking is a very important approach in ensuring that the efficiency remains at its optimum level. It is as important as checking the oil level in a .
The two valves located at the top of every cylinder head in a play important roles in the operations, without the valves being functional a lot of irregularities may become part of the operations, at its worst stage; a problem may cause the to become “unable” to start even when every other part of the are in perfect condition.
is the clearance created on the that allows it to be moved in and out of the cylinder head to allow air or fuel flow into the chamber. The action is usually made possible through the camshaft located above the sets of valves. The use of springs enables the valves to return back to their proper position after being pushed ‘IN’ the cylinder head during operation. The extent to which the is pushed into the cylinder head for air or fuel entrance or for exhaust escape depends on the clearance provided in the valves during the manufacturing. Hence, impacts heavily to the overall performance and its efficiency in fuel consumptions.
Some have tappets which automatically provide the correct setting and these do not need checking. Some need special tools for the checking of their such engines’ may only be checked by a specialist in a garage.
BEST TIME FOR ADJUSTMENT
There is two required that the should be adjusted. The adjustment can either be done while the is still hot or when the arc has gone cold. manufacturers always specify the best suitable for the adjustment in the handbook manual or workshop practical manual.
When it comes to deciding an that could be said to be ‘cold’, it is the of a cold that has stood idly overnight. While the referred to ‘hot’ is the at normal operating , which is easily measured after the has been driven for about four miles or more. However, despite the commonly used extreme opposite temperatures some manufacturers use to specify the actual their must be before any adjustment could be made to its such brands can be handed over to professionals for their valve-checking and clearance adjustment.
HOW TO MAKE
The direct acting overhead camshaft system is the easiest to but can be the hardest to because on some , 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 may specify a minimum such that the vehicle owner will have the responsibility of ensuring the valves clearances do not go lower beyond the minimum rate specified in the manual. Provided the gaps (clearances) do not go below the specified minimum figure, the will still operate satisfactorily. On most other mechanisms, adjustment of the clearances is made by turning an adjusting screw or nut and is straight-forward.
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 will point towards the exhaust valves.
Because each must be checked with the in the fully closed position, it will be necessary to turn the to them all. On in-line , it is possible to ‘pair’ the valves and save a lot of turning. For a four-cylinder , the ‘rule of nine’ can be used.
Number the valves from the generator end.
Turn the until one vale is fully open.
Subtract its number from nine, and the answer is the to . For example, when you open number 2, it should become 9-2=7, so the number 7 is the to .
The principle mentioned above can still be applied to a six-cylinder in a single line using the ‘rule of 13’ method. In this method, the can be turned by using a spanner on the nut.
To use the adjustment if the clearances are incorrect, on some , 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 is checked between the tip of the stem and the rocker pad, with the hot or cold as recommended and with the fully closed. As the camshaft is out of sight inside the , you must calculate when the lobe is pointing directly away from the tappet and the tappet is resting on the wheel. This is done by turning the until the to be adjusted is fully open, and then turning it again one complete revolution. This will rotate the camshaft a half turn, putting the tappet on the heel of the lobe. It helps to put a chalk mark on the to show when it has rotated one revolution.
Follow these steps:
- Identify the inlet and exhaust valves.
- Turn the using the rule nine or thirteen, until the is fully closed.
- 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.
- 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 have purpose-made stiff adjusting screws which do not have a lock-nut.
- Some pushrod have the adjusting nut at the center of the rocker, and the are set with the at the normal operating and running. Do not use an ordinary feeler gauge for this rather use the long feeler strips for that purpose.
- Run the at idling speed. Put a socket or box spanner on the adjusting nut. Insert the feeler blade between the moving rocker pad and stem. If the gap is too small, the feeler will be difficult to fit and the will run unevenly when it is in position. If the blade rattles, the gap is too wide.
- the nut until the runs smoothly and any feeler blade rattle disappears. If you find it difficult, stop the and the gap statically.
HOW TO CARRY OUT ADJUSTMENT ON OVERHEAD CAMSHAFT USING SHIMS
1. Refer to the handbook manual to know if the checking of the will be done when the is at its cold or at its hot .
2. the camshaft cover on the top of the . The action will require you to disconnect the high-tension at the spark plugs, note that you must mark the high-tension once you disconnect them to ensure you recognize the actual that connects with each cable after the whole operation. The action will also require disconnecting the fuel pipe at the and be removing the air cleaner from the .
3. Turn the until one lobe is pointing directly away from the tappet.
4. the manifolds to ascertain whether the is for inlet or exhaust, then use a feeler gauge to the clearance between the tappet and the heel of the lobe. Make a note of the and make a note of the clearance.
5. Turn the until the next lobe is pointing directly away from the tappet and repeat step 4. Continue this procedure until all the have been checked and noted.
6. Compare the clearances with the manufacturer’s recommendation. On single-carburetor for instance, some manufactures may state that no adjustment is necessary until the 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 to a professional to do it for you to avoid damaging any vital part of the in the process, thereby introducing an unexpected expense.
Originally posted 2018-08-12 13:25:33.
A mechanical engineer and an NDT inspector by profession. However, I love blogging and sharing of knowledge for human intellectual development, especially relating to engineering fields, environment, and science trending updates. “Engineeringall.com” is a platform for any individual with similar passion, to do so; use the “PUBLISH YOUR ARTICLE” page at the MENU to share your personal ideas, researched knowledge, or discovered incidents, etc.to those in the engineering & & the general online communities across the globe. If you love this post please share using the social buttons below.