Valve Trouble

Manawatu Times, Volume LIV, Issue 7271, 26 September 1933, Page 9

Valve Trouble

That the width of the valve seats of an engine might be an important factor in tho dissipation of the heat from tho valvo heads tias been indicated according to ovorseas oxperts by the valvo troubles which have occurred when unfavourable conditions have existed. For example, a usor of a popular model of light truck found that, although all tho mechanism was apparent iy in excellent adjustment, tho valves become pitted and “burnt out” rapidly. The fault was traced to tho valve scats, which were not wide enough to allow the heat to be dissipated quickly into into the metal of tho cylinder block and thence to the water of tho cooling system.

Tho need for having the valve scats of edequate, width will be easily appreciated when it is remembered that the valve head is exposod to the high temperatures prevailing in the cylinders during the explosion of the change, and that the period of contact of its face with the seating is only intermittent, since the valve lifts and falls at high speed when the engine i 3 running. Therefore, the time during which tho heat can be communicated to the metal of tho cylinder block is much reduced.

Another factor which must not be overlooked is the state of tho valvo stem and its guide, for the heat is also conducted from the head of the valvo stem, and so is tho to some extent dissipated through the latter's contact with tho guide. But if tho parts are worn there might be a tendency for tho value to becomo overheated.

Weak valve springs, as well as affecting the liveliness and acceleration of valves, which are not then held firmly or long enough against t.ho seatings during the fraction of time in which the valves are closod. There might, too be bouncing of the valves at certain spoeds, with a result that the burning mixture is able to reach both the faces and the seatings whore it will rapidly cause pitting and burning of the moral. When the engine is given a topoverhaul special attention should be directed to any valves which arc in a notably bad state, and the best course is to examine for all the possible causes. The average width of contact between tho valvo face and the seating is usually about 1-lGth of an inch.

It is considered by many authorties that any possible benefit derived from the use of an unduly wide seating is more than set-off by certain concomitant disadvantages.