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Page:Popular Science Monthly Volume 89.djvu/139

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Popular ScicJice Mnnt/ih/

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��that of ^hc ryliiider before it is expaiKicd by the rlanipiiisi-mit. It is tiinicd to lia\e .1 Ner\- sniootii siirfaec. In use, the drill-press is set in the back gears so the spinclle will rotate slowly, while the lap is revolving. It is also raised up and down by the hand-feed lever. The lap may be expanded slightly after it has been turned and reciprocated for a time and fresh abrasive added. Care should be taken to clean all emery and oil out of the cylinder when the lapping process is completed. If the work is properly done, all the scratches will be eliminated and a smooth bore secured. Deep scratches, such as caused by a loose wristpin, can only be eliminated by re-boring the cylinder.-ViCTOR VV. P-age.

��A Handy Hook for the Automobilist

AH.-WDY and cheap attachment for an automobile-jack is an iron hook that can be made by an>' blacksmith. It should be just a little shorter than the jack, with one end bent to fit over the top of the lifting head and the other end formed into a hook large enough to hold an axle, and strong enough to lift the car. In this way, the machine can be easily raised in places where it is impossible to set up the jack in the usual manner, for lack of clearance. The hook will be founfl particularly \aluable when the automobile gets stuck in the mud and there is no pry available. In this situation there is never sufficient clearance to use the jack, but with the hook, the car can be raised far enough to get a board, a box or some dry dirt under it. — E. F. Ayers.

���A useful hook

��Simple Cure for Misfiring at Low Engine Speeds

THE writer recenth- cured a case of misfiring at low engine speeds by a very simple expedient. The engine was a comparatively new one, and had not been run long enough to ascribe the trouble to wear in the inlet valve stem- guides. All manifold joints were tight,

��and there was no air leak around valve-caps or petcocks. The carburetor adjustment was altered without receiv- ing any benefit. A good spark was obtained from both battery and magneto systems, anil as the misfiring was as pronounced with one ignition system as

���/?eaaf Gas Poc/<ef aroi/nd SparA Points in JparA P/uq f/ectrodes Comtastion Chamlxr Misfiring can be eliminated by tapping out the valve-chamber caps

the other, it plainly was not the fault of the ignition group. The misfiring was not serious but annoying, especially when running the engine slowly on the direct-drive in traffic.

In remo\ing the spark-plugs to ex- periment with \arious gaps between the electrodes, it was noticed that the plugs did not screw into the cap very deep and that there was a pocket in the valve-cap beneath the spark-plug, as shown at A in the accompanying illustration. As every- thing else had been tried without curing the trouble, the valve -chamber caps were tapped out w-ith a J-2-in. pipe tap so the plugs could be screwed in enough to eliminate the pocket entirely as shown at B, and the edges of the tapped holes were chamfered to make sure the plug would project into the large chamber in the valv^e-cap. After the parts had been replaced, and the car- buretor restoried to its original condition, all misfiring ceased.

The explanation is that at low speeds, owing to imperfect scavenging and low rate of inlet gas flow, some dead gas left from a previous explosion collected in the small pocket around the plug- points; when the spark took place, the ignition function was erratic because of the poor gaseous mixture surrounding the plug-electrodes. Bringing the points further into the combustion chamber eliminated this condition, because the electrodes were swept by the fresh gas at every intake-stroke. -Victor \V. PAofi.

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