R. G. GRISWOLD

In machining the piston a special arbor is made to mount it on, as the truest and best work can be done in this way only. Grip the piston in a chuck or strap it to a face plate and bore out the hole in the head. Turn up an arbor two inches longer than the piston, one end of which is slightly tapered so as to drive into the bored hole. The opposite end is then provided with four tapped holes, 90° apart, to receive 1/4 or 5-16 in. screw pins.

The tapered end of the mandril is then driven into the hole and the pins screwed out against the inside of the shell, centering the open end The piston may now be turned in the lathe, and a very true cylinder obtained. The ring grooves must be cut very smooth and true, and the sides may be finished best by using a keen hand tool and scraping off a very light cut as the piston revolves. Do not allow chattering to take place, as much of the tightness of the piston against leakage depends upon the fit of the rings in these grooves. Three "water grooves" are turned in the end of the piston, which serve to carry oil to all paits of the cylinder. The head is also squared before removing from the lathe.

For boring the cross-head pin hole, make two very shallow V blocks, not over 1/4 in. thick at the bottom of the V. Strap the piston against the face plate, using these V blocks to rest it on. Lay off the centers of the inside bosses on the outside and use this point for centering. Then drill completely through, either with a 3/4 in. drill or a smaller one, finishing the hole by boring with a tool. Drilling and tapping the holes for the set screws and screwing the plug in the hole (threaded in the chuck), finishes the piston.

The rings need little description other than that they are sweated together after the bayonet joint is made and strapped to the face plate. The outside is then turned to exactly 4 in. in diameter. and after the joint is heated and springs apart, all solder is wiped off. The ring will be found to fit the cylinder perfectly. The sides are then filed perfectly smooth and true and the ring fitted in the slot. They should be a snug fit, but not so tight as to prevent any movement. Carefully spread the ends and slip over the piston, sliding them down until they " snap " into the grooves.

The connecting rod may be bored by strapping it to a block fastened to the lathe carriage and using a boring bar. The crank pin end is first drilled and the bolts fitted. Then the split is made, the adjoining sur-facefiled very smooth and the cap bolted on. The boring may then be proceeded with, exercising great care to keep the center line of the rod square with the axis of the boring bar.

The crank-shaft is centered on both ends, and the straight portions, and bearings and outsides of the crank webs finished. Two 4 1/2 in. flanges are then turned up (or two pieces of iron, 4 x 2 x1 in.) on a 1 1/4 in. arbor. A center is then drilled in each exactly 2 in. from the center of the hole. and a set screw provided for fastening the flanges to the shaft.

These flanges are then forced on the ends of the shaft with the two centers in line with the center of the crank pin to be turned, and securely fastened by the set screws. The shaft can now be put on the centers, and the pin turned, afterwards turning the flanges through 180° for the opposite pin. Wood sticks placed between the crank webs and flanges will prevent the pressure of the center distorting the shaft. When finished, mount in the center rest and bore the hole in the end to take the journal of the clutch shaft. A 5/8 in. hole is drilled in the opposite end for a pin to engage with the starting lever jaw.

The smaller details need no description. While many of the parts are marked " tool steel, " this is not absolutely necessary, as machine steel may be used and the wearing surfaces case hardened. In making fits always make them as good as you can, because the life and power of an engine depends greatly upon the quality of the workmanship.

The bearings of the crank shaft and crank-pins should be very carefully polished with fine emery powder and oil on a leather strap that can be tightly pressed against the revolving bearing.