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          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Valve Play Adjustment












Assignment

Admittedly, the subject of valve adjustment is no longer particularly appealing to motor mechanics, now that nearly all modern cars are fitted with hydraulic tappets. Indeed, this job still has to be done by truck- and particularly motorcycle mechanics.

Function

Before the valves can be adjusted, the cylinderhead must be removed. Mostly there are covers, which are held by screws or even clamps. The valves and/or their drive can also be reached sometimes by removing screw-caps. Now it is important to find out which valve, at which engine position can be adjusted. There are no problems if the camshaft is also exposed. One can then turn the crankshaft, using suitable means, until the cam is turned about 180 to the maximum valve lift.

When adjusting the cam, the most important thing to observe, is that neither the respective cam itself nor a possible offshoot thereof, comes into contact with the valve. This is why, if the camshaft cannot be seen, there are binding rules concerning the position of the engine. If these rules are not available, the engine can simply be further turned to the maximum valve-lift - in relation to the camshaft 180 - or to the crankshaft 360. Once the correct position has been found, the above shown feeler-gauge comes into play. This, having a measuring range of 0,05 mm - 0,5 mm in steps of 0,05 mm, is generally adequate. Once the prescribed point of measurement has been determined, the feeler having the required value is pulled through the gap to be adjusted. This may either be between the cam and the tappet or between the cam and the rocker-arm.

A certain amount of experience in valve adjusting is necessary to be able to judge whether the setting is exactly right or not. The feeler may not slip loosely between the parts but may also not fit too tightly. In addition, the manufacturers of motorcycles also state a measurement of, e.g., 0,18 mm, of course, the feeler-gauge doesn't have this size. Thus, one has to decide, either a tight fitting 0,2 mm or a looser fitting 0,15 mm. The best suggestion is, pull both blades through once more to see how it feels.

Hardly anything show so many differences than the technical implementation of the setting possibilities. Well known are the slot- or the Allen-screws, e.g., found on rocker arms. Using an open-ended spanner to adjust the pivot-points, shims are placed between the two surfaces. Indeed, in the history of the valve adjustment, there have even been self-locking Allen-screws. The most complex adjustment, is in the case of the Desmodromic valve control. The adjustment of the Diesel locomotive (see picture 3 above) is less complicated. In this case, two valves each are operated by one cam. By turning only one setting screw, one of the valves is given a little more play. 03/12


Too much valve-play causes ...horrible noises, ...
and loss of performance through ...lower fuel-air filling.
Too little valve-play causes ...overheating, HC-increase, ...
and loss of performance through ...loss of the fue-air filling.
In both cases ...wear and tear is possible, ...
most likely ...with too little valve-play.






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Translator: Don Leslie - Email: lesdon@t-online.de

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