The valve stem housing is not bushed and in time wears enought to emit part of the exhaust gases. This can be elimi nated by the reaming of the housing and the insertion Of a brass tube of the correct diameter and bore. The exhaust pot has a water drip connection for the purpose of maintaining the tem perature at a reasonably low value. A drip cock is also a useful adjunct to the pot since it will free the chamber of tarry deposits. The junction of the pot and cylinder head is sealed by a copper gasket. It is absolutely necessary that the stud bolts have clean threads for they are rather inaccessible, and if the stud nuts are not tight the gasket will blow.
Admission Valve.—The admission valve is contained in a cage, Fig. 77, and is actuated by a cam, similar to the exhaust cam, through the lever and push-rod shown. The cage has a gasketed joint at a. In placing the copper gasket on the joint and setting the valve cage into position, care is to be exercised to prevent the gasket from wedging.
Adjustments.—The valve lever, since the clearance between its end and the valve nut is large, delivers a hammer blow to this nut and the fibre washer. The washer wears rapidly while the nut gradually shears the threads on the valve stem. The valve stem can be turned down and threaded to take a smaller diameter nut; a second remedy is the employment of a cotter pin through the worn nut and valve stem. The bushings on the lever pins also wear rapidly; these can be replaced by new bushings. The pins frequently become flat, and new pins of machine steel, case-hardened, can be turned to replace the defective ones. If the pins are oiled, as they should be, little wear will occur; while the pin bearings have only oil holes, small oil cups are far more serviceable.
In regrinding this valve the unit is disassembled. The valve is reinserted in the cage and the dashpot again placed on the valve stem. This constrains the valve stem to remain in its proper position while the valve face is ground to the correct angle.
Adjusting Valve Levers.—The long nut on the upper. end of the exhaust valve push-rod is screwed on until it clears the.valve stem nuts by inch when the valve is at rest and the push-rod • is in its lowest position. The lock-nuts on both push-rod and valve stem must be jammed tight to prevent any change in this clearance when the engine is running. The upper end of the admission .valve push-rod is adjusted to allow the valve end of the rocker to clear the fibre washer by inch when the valve is seated..
A layout of the valve, mechanism is Fig. 7. This also includes the fuel valve rocker arm and rod. The cams are of cast steel keyed to the camshaft. Change in the timing of the cam assembly can be effected by shifting the cam gear a tooth or two: This is made possible by sliding the idle gear until it is out of mesh with the cam gear. Alteration of an individual cam is obtained by the employment of an offset key which will ove the cam the required amount.
Valve 79 gives the timing of admission, exhaust and fuel valves on the 225 h.p. American-Diesel engine. These timings represent standard practices and are equally applicable to 120 and 170 h.p. engines of this make. In this diagram each quarter circle represents 180 degrees and not 90 degrees, being equal to one complete stroke of the engine piston. The degrees indicated are to he laid off on the fly wheel rim and are not percentages of the piston travel. To translate these degrees to inches on the periphery of the flywheel is a matter of simple mathematics. For example, if the wheel be 8 feet in diameter, the circumference-is 302 inches.
One degree is in this case 302/360 - inch or .83 + inch. If the operator uses a value of .8 inch per degree, he will be working amply close.
Busch-Sulzer Type B Diesel Valves.—In exterior form the admission and exhaust valves and cages are quite similar. Both are placed vertical in the cylinder. The interior arrange ment of the cages, however, are by no means identical. The exhaust valve cage has a removable valve stem bushing; the cavity between this bushing and the cage body constitutes the cooling water jacket. The admission valve cage has the valve stem support cast integral with the cage proper. Both cages are provided with removable seats as appears in Fig. 80. This feature is of importance to the operator since it obviates the necessity of replacement of the complete cage when the valve seat has been worn excessively.
The valves, both admission and exhaust, have cast-iron bodies with steel stems. In disassembling the valve, the lock-nuts D and E are unscrewed, the valve being held by a pin wrench inserted in the' two pin holes in the valve body. The removal of the spring cap F allows the valve to be withdrawn. The exhaust valve seat, of course, experiences the greatest wear; consequently frequent refacing of the cage seat becomes neces sary. After a number of refacings with a reamer the cage seat lies too deep in the cage; when this occurs, a new removable seat ring can be obtained.