MARINE ENGINES.

387

them quite fair; by this means the turned bolts fit the holesexactly, and good firm work is obtained. The flanges at the topand bottom are planed, and the latter are cast along with theflanges for bolting down the cylinder on the keelsons. Raised partsshould be left on the casting at all the places where the bolts arearranged; in this way an even face is easily made for screwing thenuts up against, which helps to secure first-rate work.

The cylinder cover should be a deep and strongly-ribbed casting,fitted with a central manhole door, through which the bolts of thepiston and piston rods may be inspected without requiring to breakthe joint of the cover, which is a somewhat difficult task at sea,

Fig. 269.—Cylinder Covers.

a a, Covers, b b, Manhole covers. c c, Recesses for piston-rod nuts. d, Recess for air-pump rod nut.e, Hole for relief. f, Recess for single piston-rod nut.

more especially with large and heavy covers. The number of boltsshould be carefully calculated, so as not to have a great prepon-derance of strength in that part, for in the event of the coverreceiving a violent blow from the piston striking against water inthe cylinder due to violent priming, when the flanges in the cylinder