ENGINE CONTROL.

Franklin Times, Volume XIX, Issue 138, 27 November 1929, Page 7

ENGINE CONTROL.

Most new cars of advanced design are fitted with a device called an automatic spark advance. This little mechanism, that so greatly assists the motorist in controlling his engine, is housed in the body of'the distributor and operates very much like the ball governor of a steam eDgine.

It consists of a pair of weights, v.hich whirl around with the distribu-tor-shaft and tend to be moved away fj'om it by centrifugal force. These weights are so linked up with the breaker-cam that the faster they

whirl, with increasing engine • speed, the further they stand away from the shaft, thus more they advance the Lrcaker-cam in relation to its shaft, thus producing the earlier spark required by the increase in engine speed.

Centrifugal force, acting on the weights, to advf-nce the breaker-can, is resisted by a spring, which pulls the weight back toward the shaft and retards the cam and the spark, as the engine slows down and less advance s required. The device is remarkably reliable and accurate, despite its delicacy, but as its corect functioning is entirely dependent upon the spring, this must be of exactly corect strength and must be different for nearly every model of engine. If it is too strong, ignition is not advanced enough and speed and fuel economy suffer and if it is too weak, advance is excessive and knocking and loss of power will result. Occasionally cars are sent out with advance mechanisms having imperfectly calibrated springs, giving "advance curves" which do not fit engine

requirements and changes in spring strength due to service sometimes take place and make timing incorrect. Moving parts of advance mechanisms should" operate with perfect freedom or the advanoe and retard movements will be incorrect and ignition will be improperly timed. In rare instances the parts may stick in a certain position and fail to assume, promtly at least, the positions they Should occupy as engine speed changes. Lubrication is depended upon to prevent such binding—an oil supply Delivery to the distributor base usually being depended upon to reach the advanced parts. In obscure cases of spark-knock and sluggish pick-up, not traceable to ordinary causes, defective operation of the automatic advance may be suspected and a complete new distributor should be temporarily installed to determine whether this suspicion is warranted or not.