THE ENGINE PROPER 69 



cross-head until the piston just strikes the cylinder-head 

 as the crank passes the head dead-center ; then screw in the 

 rod until the piston just strikes the other cylinder-head 

 as the engine passes the other dead-center carefully count- 

 ing the number of turns of the rod. Now unscrew the rod 

 half the number of turns counted and the clearance will 

 be divided. Tighten the clamp bolt and the jam nut. 



Packing Piston-Rod and Valve-Rod. A suitable 

 packing for this purpose is the kind known as "gum-core" 

 which is round in section and has a rubber center with a 

 woven fabric covering. There are many other kinds of 

 good packing on the market. Italian hemp (which comes 

 in the form of a rope), candle wicking and similar pack- 

 ings can be used, but a rod stuffing-box packed with them 

 requires continual attention, whereas if packed with "gum- 

 core" or other good packings it will often run a whole 

 season without re-packing. 



Packing Cylinder-Head and Steam-Chest Cover. Usu- 

 ally sheet asbestos is used for the gaskets under steam- 

 chest cover, cylinder-head, governor-base flange and other 

 similar steam joints. There are some sheet-rubber pack- 

 ings that are very good. Many engine-men do not know 

 that a sheet-asbestos gasket when broken in separating 

 the parts, even when a portion adheres on one side and the 

 rest on the other, will hold tight providing that the pieces 

 of the gasket go back in exactly the same position as be- 

 fore. With either rubber or asbestos sheet packing, if 



