New Simms Battery-ignition Set
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AS the result of some years of experimental works, Simms Motor Units, Ltd., Percy Buildings, Grease Street, London, W.1, has produced a battery-and-coil ignition set for commercial vehicles. The mechanical unit—that is, the distributor head—is robustly made, so that it shall give continued reliability, despite being mounted on an engine block, the temperature of which may be in the neighbourhood of 100 degrees C.
All bearings, including the contactbreaker pins and the cam and contact breaker, are positively lubricated by using a wick feed from the base of the distributor, this being supplied with oil from an oiling box that is placed in a conspicuous position.
The well-known Simms centrifugal, automatic-advance device is accommodated in the base, and, as the distributor is above it, over-lubrication is net likely to occur. Due to the positive oil feed, the angle at which the distributor is mounted is immaterial. Another point of importance is that it has been realized that any slack between the main spindle and its bearing would prevent the cam from rotating truly and would cause unequal breaking of the contacts. To obviate this a ball bearing has been placed immediately beneath the earn.
Consistent with high-speed running, * synchronized pairs of contacts, working in parallel, ensure perfect contact at high speeds and reduce wear.
The condenser is housed in an aluminium box on the outside of the distributor casing and connected directly across the contacts. It is made of mica in preference to waxed paper, owing to the possibility of the latter failing at high temperature. The coil, which is designed to ensure low consumption, has a stout cylindrical casing, with good insulation, and is wound in a manner similar to that employed with the Simms magneto armatures.
According to the requirements of individual engines, the automatic-advance device can be calibrated to give an adjustment equal to 60 degrees of the crankshaft revolution. In addition, manual advance is available.
The set has been designed mainly for manufacturers to adopt as a standard component, but a conversion drive is available to permit existing engines to be changed over to coil ignition.
Simms Motor Units, Ltd., has produced an interesting adaptation of its automatic-advance device for fitting to standard engines, in particular the Leyland power unit as employed in the Titan chassis. In this case the unit is mounted on the front face of the crankcase, in place of the cover plate over the head of the magneto-drive Shaft. The two ball races for this shaft remain undisturbed, but a tube-and-shaft drive is substituted, the automatic adjustment taking effect between the two.
The arrangement is claimed to be highly satisfactory, because oil reaches the centrifugal mechanism from the crankcase and is fed between the tubs and its shaft by means of a wick.