Chapter VII: 75-Mm. Field Gun Model 1916

THE GUN.

Weights and Dimensions.

Weight Kg 339.74 pounds 749.
Caliber mm 75. inches 2.953
Total length mm 2,308.5 inches 90.9
Length of bore mm 2,134. inches 84.
Length of rifled portion of
bore mm 1,847. inches 72.72
Number of grooves 24
Width of grooves mm 7.30 inches .2874
Depth of grooves mm .501 inches .02
Width of lands mm 2.52 inches .0992

Twist, right hand, zero turns from origin to a point 2.89 inches from origin. Increasing from one turn in 119 calibers at a point 2.89 inches from origin to one turn in 25.4 calibers at a point 9.72 inches from muzzle. Uniform from a point 9.72 inches from muzzle to the muzzle.

Description of the 75-MM Field Gun.

=The gun= is built up of alloy-steel forgings, _consisting of a tube, jacket, breech hoop, and clip_. All of the parts are assembled with a shrinkage.

_The tube_ extends from the muzzle to the rear end of the powder chamber and two recesses are cut in its rear face to form seats for the lips on the extractors.

_The jacket_ is assembled over the muzzle end of the tube. The jacket carries two flanges on its lower side, which form guides for the gun in the cradle of the carriage, and a lug on top near the forward end which contains a T slot, which holds the recoil cylinder in place. The rear end of the jacket is threaded on the outside to receive the breech hoop.

_The breech hoop_ is threaded at its forward end and screws on to the rear of the jacket. The breech ring carries a recoil lug at the top for the attachment of the hydraulic recoil cylinder, and another lug at the bottom for attachment of the two spring piston rods. The rear part of the breech hoop is cut away to form the breech recess.

_The clip_ is a short hoop shrunk on the tube near the muzzle. It carries two lugs on its under side which form guides for the gun in the carriage.

The rear ends of the guides on the jacket are extended to the face of the recoil lugs by short extensions riveted in place to prevent entrance of dust between surfaces of the guides and their bearing surfaces on the cradle. For the same purpose the forward ends of the guides on the jacket are connected by steel-plate dust guards with the rear ends of the guides on the clip.

Description of the Breech Mechanism.

The mechanism is known as the =drop-block type=, and is semi-automatic in design in that the block closes automatically when a round of ammunition is inserted. A rectangular hole extending through the rectangular section of the breech hoop forms seat for the sliding block. The upper part of the breech hoop in rear of this slot is cut away, leaving a U-shaped opening which permits the passage of the cartridge case.

Recesses cut in both the side faces of the breech recess form seats for trunnions for the two extractors. Holes bored into these recesses from the rear face form seats for the extractor plungers, springs and plugs. The block slides up and down in the breech recess under the action of the operating arm which is pivoted on the operating shaft and acts as an oscillating crank in raising and lowering the block. The operating shaft which rotates the operating arm is actuated by the operating handle. The operating handle is provided with a latch to keep it in the closed position and is connected by a chain, piston, and piston rod to the closing spring, which is carried in the closing-spring case. The closing spring is under compression and tends to keep the block closed or to close the block when it is opened.

When the block is opened as far as it will go, it is locked in that position by the inside trunnions on the extractors. These trunnions are forced over horizontal shoulders on the block by means of the extractor plungers and holds the block in the open position. When a cartridge is pushed smartly into the gun, its rim striking against the lips on the extractor frees the trunnions from the shoulders on the block and allows the block to close under the action of the closing spring.

_A continuous-pull firing mechanism_ is carried in the recess bored out in the center of the block and is operated by the trigger shaft which projects from the bottom of the block. This mechanism is cocked and fired by one continuous motion of the trigger shaft so that in case of a misfire the primer may be struck a second blow by releasing the shaft and rotating it again. A lanyard may be attached to the projecting end of the trigger shaft.

CARRIAGE.

=Weights and Dimensions.=

Weight of carriage, complete, fully equipped, without
the gun 2280 pounds
Weight of gun and carriage fully equipped 3045 pounds
Weight of lunette, carriage limbered 140 pounds
Diameter of wheels 56 inches
Width of track, center to center of wheels 60 inches
Length of recoil of gun on carriage, variable recoil 18 to 46
Height of axis of gun about ground 42 approx.
Amount of elevation with elevating handwheel 42 degrees
Total limits of elevation 7 to plus 53 degrees
Maximum traverse either side of center 400 mils
Over all width of trails, spread 130 inches
Over all length, muzzle of gun to end of lunette 173 inches
Limits of elevation with angle of site handwheel, minus
7 degrees depression to 11 degrees elevation.

Description.

_The carriage_ is of the split trail, variable long-recoil type. The length of recoil is regulated automatically, so that the breech of the gun will not strike the ground on recoil at an angle of elevation of less than 47 degrees. At elevations greater than 47° a hole must be dug for the breech in recoil.

The gun is mounted in slides on a _cradle_ formed by the spring cylinder. The spring cylinder is suspended by trunnions mounted in bearings in the top carriage, which is supported by the pintle bearing to which are attached axle arms bearing in the wheels.

The carriage has an _independent angle of site_ elevating mechanism, by means of which a maximum depression of seven degrees and an angle of elevation of 11 degrees may be obtained. The remaining elevation is obtained through the elevating handwheel.

=The principal parts of the carriage are:=

Trail
Cradle
Recoil mechanism
Top carriage
Pintle bearing
Equalizing gear
Shields
Angle of site mechanism
Elevating mechanism
Traversing mechanism
Axle seat
Brake mechanism
Shoulder guards
Firing mechanism
Sight, model of 1916
Wheels.

LEFT ELEVATION.]

RIGHT ELEVATION.]

_The trail_ is made in two halves of box section built of bent and riveted steel plate. Each half is bolted to a lug on the equalizing gear, so that it may be rotated horizontally from the junction point of the trail to the point where the trail hits the wheel.

The trails are locked together in traveling position by means of a cone-shaped vertical lug on the lunette bracket which fits in a socket in the trail coupling, and is locked in place by the trail-coupling latch. Trail-coupling latch has a handle and catch with a vertical spindle seated in a socket in the lunette bracket. A handle-return spring is assembled around the spindle and the latch engages a catch on the trail coupling when trails are fixed in the traveling position. Latch is opened by moving handle forward.

_Lunette_ consists of a ring for attaching the carriage to the limber and is bolted through the lunette bracket.

_Floats are_ attached to the bottoms of both trails at their rear ends, consisting of flanged steel plates for the purpose of increasing bearing area of the trails on soft ground.

_Spade bearings_ are riveted to rear of the trails and form bearings for spades in firing position. Spades are driven through the bearings, and their upward movement relative to the trails is prevented by spade latch.

_Spade-latch_ bracket consists of a bronze plate with a cylindrical chamber for a spring and plunger and two bearings for latch-handle pin. Bracket is riveted to the inside top of trail in front of the spade. Spade-latch plunger, with a spring assembled around it, is seated in the chamber and the spade-latch handle is pinned in the bearing. Top of handle extends through the trail and is roughened for use as a foot pedal. Lower part of handle engages with the plunger. When the spade is driven the plunger is forced into a notch in the spade by means of the spring, and the slope on face of plunger allows a downward movement of the spade and prevents upward movement. To release spade the foot pedal on latch handle is pressed down, disengaging plunger from spade, and the spade is removed.

_Trail handles_ are riveted to outside of both trails for lifting trails. Name plate is riveted to outside lower left trail. It is important that the number of carriage on this plate be recorded by the officer in charge of the unit to which it is assigned and that this number be used as a reference in all correspondence. Wheel guards, rear, are plates riveted to the outside lower left of both trails for the protection of trail bodies against contact with limber wheels on short turns. Trail guards are bent plates riveted to the top of trail in front of trail-coupling latch to prevent battering of trails by sledges used for driving the spades.

_Sponge-staff_ fastenings are riveted to tops of both trails. Sponge staffs are inserted in upper rings of staff fastenings and the lower ends are clamped in place. The smallest section of sponge staffs fits in sponge fastenings.

_Sledge fastenings_ are similar to sponge staff fastenings and are riveted to the outside of each trail. Wheel guards (front) are plates riveted to the outside of trails near the front to prevent contact of trails with wheels when the trails are separated.

_Spare parts_ case is a steel box with a hinged steel cover provided with a bolt snap and padlock riveted to the outside of front left trail. This case contains spare parts for emergency use.

_Trail seats_ are made of formed bent plates riveted to the tops of trails near breech of gun. Oiler support with springs is under the right-hand trail seat. Oiler rests on this support and is held in place by springs.

REAR VIEW.]

PLAN VIEW.]

_Traveling lock bar_ consists of a forged steel bar pinned to lock bar bearing on left trail and made to swing across trails in traveling position and along left trail in firing position. In traveling position the socket in the middle of the lock bar engages with the traveling lock stud in the bottom of cradle, and right end of lock bar is held in lock bar clip on right trail by the latch. To disengage the latch for firing, the latch handle is lifted and the lock bar swung to fastening in left trail, where it latches.

_To lock the cradle_, the gun is brought to 0 azimuth and the traveling lock pointer on right trunnion cap brought to line marked “March.” In this position the traveling lock socket fits over stud, and the lock is latched. The latch consists of a lever pinned at one end to the lock bar with a plunger pinned in center extending through the bar with a spring around the plunger body to hold the latch in place.

Trail connections are riveted to front end of trail and bolted to equalizing pinions.

=The cradle= comprises the spring cylinder with attached parts.

The spring cylinder is below and shorter than the gun. It is in the form of two cylinders joined at the center, with axes in the same horizontal plane. Above the cylinders are the gun ways, parallel to the cylinders, bronze lined, and opening toward the center line of cylinders. Traveling lock stud is bolted through a lug at the rear and below the cylinders. Firing-shaft bracket is riveted to the left side and range-scale bracket to the right side of the cylinder at its rear end. Shoulder guards are pinned in sockets in both firing-shaft and range scale brackets to prevent contact of the gun during recoil, with the cannoneers. Trunnions are riveted and keyed to the cylinder near center. Elevating arc is bolted to lugs on the bottom of cylinder at trunnions. Piston-rod bracket is riveted to projections on the cylinder above the gun slides near the front end. Cylinder cover is pinned to cylinder clips, which are riveted to the front of spring cylinder. (Note: On some carriages the clips are made integral with the cylinder.)

LONGITUDINAL AND TRANSVERSE SECTIONS]

=The recoil mechanism= is designed for variable recoil, the length of which is regulated automatically by the elevation of the gun. The following table gives lengths at various elevations: (These lengths are based on theoretical calculations. Actual lengths of recoil between 8’ and 45’ elevation are generally greater.)

Elevation. Length of Recoil.
-7.0 to plus 8.0 degrees 46 inches.
-8.0 to plus 16.47 degrees 46 to 28 inches.
-16.47 to plus 27.20 degrees 28 inches.
-27.20 to plus 36.7 degrees 28 to 18 inches.
-36.7 to plus 53 degrees 18 inches.

The breech of the gun on short recoil will strike the ground at the level with the bottom of the wheels at an elevation of 47 degrees or over.

_The recoil mechanism_ is of the _hydraulic spring type_, with the _recoil cylinder_ mounted above the gun and the counter-recoil springs in the cradle below the gun. The recoil cylinder is held in place by a slot machined in the gun jacket at the front and rests in the cylindrical opening in the gun lug above the rear of the gun. It is held in place by the cylinder retainer, which screws into the rear cylinder parallel to the center line.

_The recoil valve_ is a cylinder with a collar at the front end and three lands inside and parallel to the bore. Three rows of holes are bored at the lands. The recoil valve fits inside the cylinder, resting on the lands, and is held in place by a collar bearing against the edge of the counterbore in the cylinder at the front, while the rear end of the valve bears against the inside rear end of the cylinder.

_The piston_ is screwed and pinned to the piston rod and is of bronze, slotted to fit lands and grooves in the recoil valve. The piston rod is hollow for almost the entire length. The front end passes through the gland in the cylinder head and piston-rod sleeve. The front of the recoil cylinder is closed by the front cylinder head, which is screwed in place with a gasket. A bronze gland with four rings of 5/16 inch Garlock packing prevents leakage around the piston rod.

_The counter-recoil buffer_ consists of a buffer rod screwed into the buffer nut at the rear end of the recoil cylinder, and extending through the buffer bushing into the interior of the piston rod. The buffer head is screwed and pinned into the front end of the buffer rod. The buffer head is of two diameters and connected by a short cone. The rear end is the smaller diameter and is threaded inside to screw over the buffer rod. The coned surface contains slots leading to a hollow chamber in front. The front end of head is faced and provided with a central bearing for valve stem. The bearing is supported by webs to main body of guide. Valve stem has a stop on rear and a valve screwed to front. Valve is faced to seat on front of the bearing, webs and circular face of main body of guide.

_The counter-recoil springs_ are assembled around _spring rods_ in _spring cylinder_. Spring rods fit in gun lug and are fixed in place by taper keys driven diagonally through lug and rod. The rod is hollow for entire length, except at the rear, where the outside diameter is decreased to permit entrance in gun lug. Collars are screwed and pinned to front ends of rods. _Three coils of inner counter-recoil springs_ are assembled over the spring rod, surrounded by _three coils of outer springs_. Inner and outer springs are coiled in opposite direction to prevent nesting, and sets of coils are separated by a bronze separator. Rear ends of cylinder are bushed for spring rods.

_The operation of recoil mechanism is as follows_:

When the gun is fired it moves back in slides on cradle, carrying with it spring rods, buffer rod, recoil cylinder, and recoil valve. The piston, piston rod, and spring cylinder remain stationary, being fixed to carriage.

LONGITUDINAL SECTION, RECOIL AND COUNTER RECOIL MECHANISM]

The recoil cylinder being full of oil, this oil is forced by the piston through holes in recoil valve in front of piston up into annular space between valve and cylinder and into space behind and vacated by the piston. The hydraulic resistance caused by forcing the oil through the holes in valve absorbs most of the recoil energy of the gun, and the remaining energy is taken up by compression of the counter-recoil springs and friction.

When the gun reaches the end of recoil all of the recoil energy has been absorbed and the counter-recoil springs acting against spring-rod piston force the gun back to battery position. The purpose of the counter-recoil buffer is to overcome the tendency for gun to return to battery too rapidly, at the same time allowing sufficient speed of counter recoil to permit maximum rapidity of fire. Buffer action is necessary, as the strength of springs required to return the gun to battery at high elevations is greater than is required at lower elevations.

The action of counter-recoil buffer is as follows:

As the buffer rod moves backward in piston rod the valve in buffer-rod head is opened by the pressure of oil in back of valve and the vacuum in front, which forces oil into buffer chamber in front of the buffer-rod head. At full recoil the buffer chamber is full of oil and buffer-rod head is inside the rear end of piston rod. When springs force gun back in counter recoil, buffer rod moves forward, compressing oil in chamber and forcing valve closed. This prevents escape of oil through valve and forces oil to throttle between outside surface of buffer-rod head and inside surface of piston rod, offering resistance to spring action and thus easing the gun into battery. The inside bore of piston rod is tapered at front end to increase resistance and obtain desired decrease in counter-recoil velocity.

If guns fails to return to battery after a few rounds of rapid firing, it is probably due to expansion of oil. This may be determined and corrected by loosening filling plug. If oil spurts out, allow it to run until gun is back in battery. It may be necessary to relieve oil two or three times immediately after filling. Gun should never be allowed to remain out of battery more than 1 inch on counter recoil without determining and correcting the cause.

If gun remains out of battery and the relief of oil does not cause it to return, it is due to:

(a) Weak or broken springs; (b) piston-rod gland too tight; (c) dirt or lack of lubrication in gun slides; (d) distortion of gun on gun ways; (e) distortion of piston rod due to improper counter recoil action.

The majority of cases are due to (a), (b) and (c).

(a) Can be determined only by removing springs, and should be undertaken only after all other methods have been tried.

(b) Can be determined by loosening piston-rod gland. If gland is too tight, gun will return to battery when it is loosened. If gland cannot be loosened, piston-rod is probably distorted.

(c) Flood slides with oil, and if possible retract gun and examine gun ways and slide for dirt.

(d) If possible allow gun to cool for 15 or 20 minutes. In case of (a), (c) or (d) gun can generally be pushed back into battery by hand.

(e) If piston rod or interior mechanism is distorted, mechanism must be disassembled and defective parts replaced. If distortion has occurred, it can generally be identified by very rapid counter recoil for round on which gun does not return to battery. This may be caused by foreign matter in oil causing buffer valve to stick, or by lack of sufficient oil. If distortion has occurred, it will be near gland and can generally be felt by running hand along rod from bracket to gland.

VALVE TURNING GEAR AND RECOIL CYLINDER ASSEMBLED.]

In case of any improper functioning of recoil mechanism during recoil or counter recoil, cease firing until cause has been determined and corrected. A piece is out of action when recoil mechanism is not operating properly and will almost certainly be damaged seriously if further firing is attempted.

After dismounting any part of recoil mechanism or filling recoil cylinder, gun is to be retracted and released to allow counter recoil if possible. In performing this test, valve-turning mechanism must be disconnected and valve turned to correspond to an elevation of carriage of 53° before gun is retracted. Gun must not be held out of battery more than 10 seconds before being released.

=Variable recoil= is obtained by varying the area of effective throttling holes in the recoil valve. An arm on the trunnion cap is connected by means of connecting rod, valve-turning arm, valve-turning gear, and a piston-rod gear, to the piston rod itself. As the gun is elevated the relation of the cylinder to the trunnion changes, causing the piston rod to turn by means of the valve-turning mechanism. Slots in the piston engage lands in the valve, causing the valve to turn with the piston. As the cylinder remains stationary the location of the lands inside of the cylinder change with relation to the three rows of holes in the valve, and these rows of holes are covered to produce variations in the length of recoil. At long recoil all the rows are uncovered; at intermediate recoil one row is uncovered; and at short recoil two rows are uncovered. The setting of the valve in degrees elevation is shown by the scale on the piston-rod sleeve and index mark on the edge of the piston-rod bracket bushing at the top of the piston rod.

=The top carriage= carries trunnions of the spring cylinders and rests on pintle bearing. The top carriage bears on the circular bronze slides in upper part of pintle bearing and is centered on the bronze pintle collar of the pintle bearing.

=The pintle bearing= carries the top carriage, the equalizing pinions and the equalizing gear, and is supported by the axle arms, which are shrunk in the arms of the pintle bearing. Axle arms bear in the wheels.

The object of the =equalizing gear= is to increase the stability of the carriage in firing when the wheels are at different elevations. Equalizing gear is an H-section with bevel tooth sector on each end and bronze-bushed bearing in the center. It bears over the vertical journal below the pintle bearing and is held in place by equalizing-gear support screwed inside the journal. Vertical deflection is prevented by the equalizing-gear bolts which are fixed to the pintle bearing by means of nut and shoulder, pass through slots in equalizing gear, and support gear on bolt heads. Equalizing pinions are bevel pinions sectors, bronze bushed, bearing over the arms of the pintle bearing, and have the lugs for trail connection bolts. Pinions are held in place by locking rings screwed over axle arms and are free to revolve about the pintle bearing arms.

Equalizing pinions mesh with equalizing gear.

When the carriage is laid with wheels at different elevations, it is more unstable than when wheels are level. If fired under this condition, the force of recoil tends to overturn the carriage. The function of the equalizing gear is to overcome this tendency. When carriage is fired, firing stresses are transmitted to trails, and the side on which the smaller stress is exerted tends to rise. This motion is transmitted through equalizing pinion and equalizing gear to equalizing pinion on other side, applying downward force on this trail and preserving the stability of carriage.

_The angle of site_ mechanism is designed to give the gun a maximum depression of about 6° and a maximum elevation of 11°, independent of the elevating mechanism. The mechanism is operated by two handwheels, one on each side of gun.

DIAGRAM OF ANGLE OF SITE MECHANISM.]

Handwheel on right side operates through bevel gear on handwheel shaft and intermediate shaft, both mounted in angle of site bracket, right, and cross shaft mounted in bronze bushings in top carriage. Handwheel on left side operates through bevel gears on handwheel shaft, mounted in angle of site bracket, left, and cross shaft mounted in bronze bushings in top carriage. Bevel gears on ends of both cross shafts mesh with bevel gear on angle of site worm, which is mounted in bushings in top carriage and held in place by angle of site-worm caps. This worm meshes with teeth cut in rocker.

Rocker is a U-shaped piece with bearings at the tops of both arms and teeth cut in bottom of U. The bearings bear over and are free to revolve about trunnions on cradle independent of trunnion bearing in top of carriage. Top half of right bearing is formed by rocker arm, right, which extends back and carries angle of site scale, pointer, rack, and level and forms a bearing for elevating handwheel shaft. Rear of rocker arm, right, is braced by rocker arm brace, a diagonal hollow rod attached to rocker arm and rocker. Top half of left bearing is formed by rocker arm, left, a diagonal arm extending upward to the rear to form a support for sight. Movement of the angle of site mechanism is limited in elevation by the rocker stop bolted to the side of the rocker and in depression by a screw in the arc.

=The elevating mechanism= is designed to allow an elevation of the gun of 42° independent of the angle of site mechanism. The mechanism is operated by one handwheel on the right side of carriage, which is turned in a clockwise direction to elevate gun.

ELEVATING MECHANISM.]

The elevating mechanism is operated through bevel gears on elevating handwheel shaft mounted on a rocker arm, right, elevating intermediate shaft inside rocker-arm brace, elevating cross shaft, mounted in an elevating cross-shaft bearing bolted to the rocker, and the elevating worm, which bears inside lower part of the rocker. The elevating worm meshes with the elevating arc, which is bolted to the bottom of the spring cylinder.

In indirect fire the angle of site in mils is laid off on the angle of site scale with the pointer and the desired range of graduation brought opposite the pointer by means of the elevating handwheel.

=Operation of the Angle of Site and Elevating Mechanism.= The angle of site mechanism is operated by turning handwheel, the movement of which is transmitted through the shafts and gears to the angle of site worm meshing with the rocker. Movement of the rocker is transmitted directly through the elevating worm, elevating arc, and spring cylinder to the gun, and through the rocker arms to the elevating mechanism, gun, cradle, and sights. The elevating mechanism moves only gun and cradle through movement of handwheel shafts, and the elevating worm inside the rocker, which meshes with the elevating arc.

The angle of site scale is graduated in mils from 170 to 500. The range scale is graduated in meters. The zero setting of the gun is with O on the range scale opposite 300 on the angle of site scale and the level bubble on the rocker arm, right, at the center of the tube. This allows the maximum depression of 7 degrees (about 130 mils) or the maximum elevation of 11° of angle of site mechanism to be read on the angle of site scale against the zero of the range scale.

The sight, model of 1916, which acts as a support for the panoramic or peep sight, is attached to the rocker arm, left.

TRAVERSING MECHANISM.]

In direct fire, the axle of the bore is brought on the line of site by operating the angle of site handwheel until the cross hairs of the sight are on the target and the range is laid off independently by bringing the desired range graduation opposite 300 on the angle of site scale. Line of site may be set independent of the range, as there are two angle of site handwheels.

=Traversing Mechanism.= The total traverse of the gun on the carriage is 800 mils. The traversing handwheel is located on the left side of the carriage and turns in a clockwise direction for left traverse.

The traversing handwheel shaft is mounted in the angle of site bracket, left, and the angle of site bracket cover, left. A bevel pinion on upper end of the shaft meshes with bevel gear on traversing shaft, which bears in angle of site bracket, cover, left and intermediate shaft bearing bolted to top carriage. A bevel pinion at lower end of the intermediate shaft meshes with bevel gear on end of traversing-worm shaft, which is mounted in bearing in top carriage. Traversing worm meshes with traversing rack which is screwed to pintle bearing. Traversing stops are filister head screws between end teeth of traversing racks to limit movement of worm in rack.

The movement of handwheel is transmitted through shafts and bevel gears to worm and rack. Rack is mounted in pintle bearing, which remains stationary, and top carriage moves about its bearing in center of pintle bearing and bronze-lined slides around the outside of pintle bearing. Traversing scale is screwed to pintle bearing above rack, and pointer is formed on traversing worm-shaft bearing.

DISMOUNTING AND ASSEMBLING CARRIAGE.

Note.—The first and most important precaution to be observed in assembling guns and carriages is that all parts must be clean.

Where dismounting but not assembling operation is described, assembling is approximately the reverse of dismounting.

I. To remove recoil cylinder.
II. To disassemble recoil cylinder.
III. To assemble recoil cylinder.
IV. To dismount gun.
V. To remove counter-recoil spring.
VI. To remove breechblock.
VII. To replace piston rod, gland pkg.
VIII. To remove wheel.
IX. To remove shields.
X. To remove spring cylinder.
XI. To remove sight.
XII. To remove rocker and rocker arms.
XIII. To remove top carriage.
XIV. To remove equalizing gear and pinions.
XV. To remove brake mechanism.
XVI. To remove trails.

I. To Remove Recoil Cylinder.

1. Remove valve turning gear cover (take out four ⅜” bolts attaching it to the piston rod bracket).

2. Remove valve turning gear, valve turning arm and connecting-rod as a unit by removing split pin, nut, and connecting rod pin from trunnion cap, right.

3. Remove piston rod (remove lash wire and two 3/16” split pins) slide piston rod gear forward and remove.

4. Remove ¼” locking screw from top of piston rod bracket.

5. Remove 3/16” cylinder retainer screw and loosen cylinder retainer, but do not remove retainer.

6. Remove brass spring-rod plugs from rear ends of both spring rods.

7. Screw spring compressor eye into rear of left spring rod. Make loop in compressor and attach double sheave close to cradle. Attach single sheave to lunette by means of loose cord of sheave rope.

8. Man pulling rope with from four to six men, retract gun not less than 10”, and secure rope to lunette.

9. Remove cylinder retainer, slide cylinder forward until free of groove in gun and remove cylinder. Handle carefully.

10. Allow gun to return to battery slowly by slacking off on pull rope.

II. To Disassemble Recoil Cylinder.

Note.—The interior parts of recoil cylinder are made with great accuracy to insure proper operation and must be handled with care to avoid injury.

1. Remove recoil cylinder from carriage. (See I.)

2. Drain recoil cylinder by resting on blocks at front and rear, removing both filling plugs and drain plug, and tipping rear end up to allow all oil to flow out of drain-plug hole.

3. Unscrew buffer-rod nut from rear cylinder head, draw out buffer rod until wrench can be applied on flats, and remove nut. Push rod back into cylinder.

4. Remove lower split pin from gland lock, swing gland lock back until free of notches in gland, and loosen gland with gland wrench. Unscrew front cylinder head with special wrench. Threads may be started by striking handle of wrench with soft hammer. Do not hold cylinder in a vise.

5. Draw out piston rod slowly, supporting it at both ends as it leaves cylinder. Hold recoil valve in cylinder with ends of fingers. Keep receptacle under front of cylinder to catch surplus oil.

6. Drain surplus oil from piston rod by holding vertically over receptacle with piston down and holding buffer rod in place.

7. Rest piston rod on blocks, remove buffer-bushing locking screw, and unscrew buffer bushing, holding piston rod by wrench on flats at front end of rod. Have supporting blocks under both ends of rod so that rod will not be strained.

8. Draw out buffer rod carefully.

9. Draw out recoil valve with fingers. Remaining parts can now be easily disassembled. Buffer head is locked in place with bronze pin, which must be driven out before head can be unscrewed.

III. To Assemble Recoil Cylinder.

This operation is the reverse of II. Be sure that all gaskets and locking screws and pins are replaced and are in good condition. Be sure that all parts of mechanism are perfectly clean and dry, and that oil is clean. Oil must be strained through double thickness of clean cloth and if clean oil is not available use new oil. Do not make piston-rod gland too tight. Tighten with hand and screw up with wrench one additional notch to lock gland. Fill recoil cylinder before replacing on carriage, as follows:

(a) With drain plug in place and filling plugs out, pour hydroline oil into filling hole slowly to avoid the formation of air bubbles.

(b) When oil is level in filling-plug openings, tilt cylinder slightly to allow escape of air and replenish oil.

(c) Loosen filling plug in front end of piston rod enough to allow oil to drip, and tighten plug.

(d) Replace rear filling plug, raise front of cylinder about 6 inches, and tap cylinder lightly with wood block or lead hammer to remove air. Level cylinder, fill, and replace front filling plug. Be sure that all gaskets are in place and properly centered.

Note.—After recoil mechanism has been disassembled and replaced on carriage gun should be retracted 46 inches and eased back into battery slowly to be sure that it is properly reassembled.

IV. To Dismount Gun.

1. Remove recoil cylinder (see I) and breechblock (see VI).

2. Raise and block up trails in horizontal position, elevate gun until axis of bore is parallel with trails, and attach retracting mechanism (see I-7) to left spring rod, retract gun about 6 inches, remove 3-16-inch split pin in left spring-rod key, and drive out key with bronze drift. Ease gun into battery slowly and permit further forward movement of spring rod until rope is slack and front end of spring-rod rests against spring cylinder cover.

3. Transfer retracting apparatus to right spring-rod, retract gun about ¼ inch, remove split pin and spring-rod key, ease gun into battery until spring-rod rests against spring-cylinder cover, and detach retracting mechanism.

Note.—In this position full pressure of springs is against cylinder cover and gun is free to slide in ways. Men should be kept from in front of spring-cylinder and care must be exercised to prevent tipping of cradle to the rear, which may cause gun to slide off.

4. Bring gun to maximum depression.

5. Lower trails to ground, spread trails against wheels, set brake, and bring gun to zero elevation.

6. Requires seven men and four pick handles or implements of almost the same length and strength. Slide gun about 36 inches to the rear by hand, place one pick handle in bore of gun at breech with one man, one pick handle with a man on each side under gun slides at front of cradle, and four men with two pick handles under gun as gun is drawn out.

7. Push gun out of ways, supported by men, and remove.

Note.—In using pick handles do not place them under dust guards at gun lugs. Care must be taken to keep gun properly supported at same level as cradle guides at all points until free of guides.

In remounting gun on cradle be sure that ways are well oiled and ways and slides thoroughly clean. Mounting gun is the reverse of IV.

V. To Remove Counter-recoil Springs.

1. Close and latch trails. (Open spring-cylinder cover.)

2. Set brake and drive one spade (to secure carriage).

3. Remove breechblock (see VI.)

4. Attach spring-compressor to right spring rod (see I-7).

5. Secure single block of retracting apparatus to fixed point, such as “dead man,” driven spade, or tree. The holding power of this fixed point must be at least equivalent to a driven spade and attaching point of rope should not be higher than center of spring rod.

Note.—Sufficient slack of rope must be allowed to permit spring compressor to travel full length of spring cylinder and be detached from spring rod at front end.

6. Retract gun about 6 inches, remove split pin in spring-rod key and drive out spring-rod key with bronze drift.

7. Release retracting mechanism gradually until spring compressor rope is slack, draw spring rod out of front end of spring cylinder, and detach spring compressor.

8. Attach retracting mechanism to spring rod, right.

9. Retract spring rod about ½ inch, remove split pin, and drive out spring-rod key.

10. Release retracting mechanism gradually until spring compressor rope is slack, draw spring rod out of front end of spring-cylinder and detach spring compressor.

Note.—Assembly of counter-recoil springs is reverse of removal. The following precautions must be observed in assembling:

(a) If tension-spring compressor brings spring rod up solid against spring cylinder bushing in rear of spring cylinder, ease off rope slightly and pry up rod with bronze drift until it will enter the bushing.

(b) Before key slot enters gun lug see that keyways in spring-rods and keyways in gun lugs are in line. If not, turn spring-rod by means of drift until keyways are in line.

VI. To Remove Breechblock.

1. Remove operating-shaft detent, slide operating handle to the right as far as the chain will permit, remove 1-16 inch split pin from studlink pin.

2. Remove chain, piston rod, spring piston, piston-rod nut, and locknut as a unit by drawing out of closing-spring case.

3. Remove closing spring from case.

Note.—For complete instructions regarding disassembly of the breech mechanism see page 19.

4. Remove trigger-shaft detent split pin and trigger-shaft detent by drawing it out of the breechblock to the right.

5. Remove trigger shaft by prying gently straight down with screw driver or similar tool. Keep breechblock supported for all succeeding operations.

6. Remove operating handle by sliding to the right and off operating shaft.

7. Remove operating shaft by sliding to the left.

8. Raise breechblock as far as possible (about 3-8 inch), move bottom part of operating arm to the rear, and remove operating arm.

9. Remove breechblock by sliding down free of breech ring.

10. Remove extractors by sliding toward center line of gun.

VII. To Replace Piston Rod Gland Packing.

(Packing, 4 rings, 5-16-inch square Garlock hydraulic packing.)

(Gun in battery or cylinder removed.)

1. Remove lower split pin from gland lock, swing gland lock up out of notch in gland.

2. Unscrew gland with special wrench and slide forward on rod.

3. Remove packing with bent wire.

4. Insert five rings of new packing, one ring at a time, and push each ring home with packing tool of copper or hardwood to fit into gland recess. Break joints in rings and tap packing tool lightly with hammer to drive each ring of packing home.

5. Screw up gland by hand and not more than three additional notches with wrench so that gland lock will catch and replace split pin.

Note.—For the first few rounds after inserting new packing there will be some leakage at gland and occasional tightening will be necessary. Gland should not be screwed up tight with a wrench, as it can be made sufficiently tight by hand to prevent leakage if properly packed.

VIII. To Remove Wheel.

1. Raise and support carriage under equalizing gear near each end (about 12” each side of center.)

2. Disengage hubcap latch; unscrew and remove hubcap.

3. Disengage wheel fastening plunger and remove wheel fastening.

4. Remove wheel.

IX. To Remove Shields.

A. Top shield.—1. Remove four ⅜” pins, two ⅜” locking pins, and lift off shield.

B. Apron.—1. Remove four ⅜” hinge pins and remove apron.

C. Cradle Shield.—1. Remove two 3/32” split pins, nuts and bolts. On carriages number 625 to number 678 inclusive, remove two cradle shield extensions.

D. Main Shield, left.—1. Remove six ½” bolts from shield bracket outer left. 2. Remove three ⅜” bolts from shield socket, inner left. 3. Lift off shield.

Main Shield, right—1. Remove right wheel (see VII). 2. Remove ½” pin from brake band end, remove adjusting nut and force (by hand) brake band out of position, to clear main shield, right. 3. Remove four ½” bolts from shield bracket, outer right, and two ½” bolts from brake lever bracket. Remove two 2/16” bolts from tool and remove tool carrier. Remove three ⅜” bolts from shield bracket, inner right. 4. Lift out shield.

X. To Remove Spring Cylinder.

1. Remove recoil cylinder (I), gun (IV), counter recoil springs (V), sight (XI) and shields (IX).

2. Remove trunnion caps (right and left) by raking out four split pins, loosening swing bolt nuts, and withdrawing ½” trunnion cap pins.

3. Remove rocker stops (right and left) by taking out four split pins and ⅜” bolts.

4. Unlatch and spread trails.

Note.—Seven men and four pick handles (or similar implements) are required for succeeding operations.

5. Post two men with one pick handle at rear, two men with one pick handle immediately in front of elevating arc, and two men with one pick handle at front end of spring cylinder.

6. Raise cradle slowly, slightly to the rear until rocker clears top carriage. Carry to the rear sufficiently to rest middle pick handle in trunnions and transfer two men with handle to rear of carriage. Continue to the rear sufficiently to rest front pick handle in trunnions, transfer men to rear, and remove spring cylinder.

XI. To Remove Sight.

1. Remove three ⅜” bolts from rocker arm, left.

2. Remove one ⅜” pin from sight lever in left trunnion.

3. Remove sight and sight link.

XII. To Remove Rocker and Rocker Arms.

1. Remove spring cylinder (see X).

2. Remove two 3/32” split pins, with ⅜” nuts and bolts, two ⅜” cap screws with lock washers, four ⅛” screws, driving out four O.247” by O.34” by O.872” keys from rocker arms, right and left.

3. Remove rocker arm, left, by sliding up and out of rocker.

4. Remove cross-shaft bearing cover by taking out three 3/32” split pins and removing three 3/16” nuts.

5. Drive out ⅛” pin from intermediate shaft pinion, remove two ⅛” split pins, two ½” nuts, one ⅛” split pin, and one ½” cap screw from rocker-arm cap and remove rocker-arm cap.

6. Lift out elevating handwheel and handwheel shaft as a unit.

7. Draw intermediate shaft up and out of rocker-arm brace, draw rocker down from trunnions (keeping in line with rocker-arm bearings) and remove. Swing rocker arm, right, up and around trunnions until free of range-scale bracket and remove.

XIII. To Remove Top Carriage.

1. Remove spring cylinder (see X) rocker and rocker arms (see XII).

2. Remove angle of site bracket, left, by removing three split pins and nuts from ⅜” bolts in angle of site bracket cover, left, taking off cover, removing nut and split pin from traversing handwheel shaft, removing handwheel and drawing shaft out to the left.

3. Remove two split pins and ¼” nuts from cross shaft pinion case (left) bolts, extract bolts, and remove case.

4. Remove cross shaft pinion case, right, as in XIII-3.

5. Remove split pins and two nuts from cross shafts, right and left.

6. Remove split pins and nuts from four ½” studs securing angle of site bracket, left, and remove bracket with attached parts as a unit.

7. Remove angle of site bracket, right, as in XII-5.

8. Draw out cross shafts, right and left, and remove cross shaft pinions, right and left.

9. Traverse top carriage to the right (by turning intermediate shaft gear by hand) sufficiently to allow traversing stop, rear to be removed. Extract split pin, remove nut, and take off traversing stop, rear.

10. Traverse top carriage to the left until traversing worm is disengaged from rack, remove split pins and nuts from four studs securing traversing worm shaft bearing to top carriage, and remove bearing and attached parts as a unit.

11. Lift out traversing worm with attached parts as a unit.

12. Turn top carriage to the right 90 degrees from zero azimuth, remove three screws that attach traversing rack to pintle bearing and remove traversing rack.

13. Turn top carriage to the right 90 degrees (180 degrees from zero azimuth), remove four screws that attach dust guard to pintle bearing and remove dust guard.

14. Remove two screws that secure clip to pintle bearing and take off clip.

15. Raise top carriage from pintle bearing.

XIV. To Remove Equalizing Gear and Pinions.

1. Remove top carriage (see XIII), wheels (see VIII), brake mechanism (see XV) and trails (see XVI).

2. Turn pintle bearing bottom side up, remove 29 screws which attach washers and binders and remove equalizing-gear cover.

3. Remove split pins and nuts from both locking ring-clamp bolts, unscrew and remove rings (one right, one left).

4. Slide equalizing pinion off axle arms.

5. Remove split pins from right equalizing-gear bolts, hold nuts tight, unscrew and remove bolt, remove nut and washer, remove left equalizing-gear bolt, nut, and washer in the same manner.

6. Remove locking screw and equalizing-gear support (using special wrench). Lift up and remove equalizing gear.

XV. To Remove Brake Mechanism.

1. Remove wheels (see VIII).

2. Remove brake bands, right and left, by extracting four split pins and removing four brake pins from ends of brake shaft.

3. Remove one split pin from each type “A” pin securing brake lever, foot to brake lever bracket and to sleeve extension. Remove type “A” pins and brake lever.

4. Extract two split pins from brake lever sleeve near center of carriage, draw out and remove brake shaft, left.

5. Remove shield bracket, outer right, brake shaft, right and brake lever sleeve with all permanent parts attached, by removing main shield (see IX, D and E), removing split pin and nut from brakehanger bolt, taking out bolt, and sliding parts off axle arm.

6. Remove shield bracket, outer left, by removing split-pin, nut, and brake hanger bolt and sliding brake hanger with permanent parts attached, off axle arm.

XVI. To Remove Trails.

1. Support carriage at front of pintle bearing.

2. Remove two split pins and nuts from connection bolts, drive out bolts with copper drift, slide trails to the rear and remove.

GENERAL INSTRUCTIONS.

Filling Recoil Cylinder (Cylinder Mounted on Carriage.)

If the recoil cylinder is not completely filled, loss of stability will occur and there is danger of serious damage to material. Before firing, a commissioned officer should always verify the filling of cylinder by removing one filling plug (with gun level) in which case oil should be visible above recoil valve.

To fill recoil cylinder when assembled to carriage, elevate the gun about five degrees, remove both filling plugs and pour Hydroline oil in slowly with funnel until oil appears at rear filling plug hole. Level gun and again fill until oil appears at both filling holes. Shake carriage gently and continue to refill slowly until air ceases to come out of cylinder. Replace rear plug, elevate gun about five degrees, remove valve turn-gear cover, and loosen plug in end of piston rod sufficiently to allow oil to drip out. As soon as oil starts to drip, tighten plug; be sure that gasket is centered. Replace rear filling plug, rock carriage to permit air to escape from filling hole and fill with oil. Replace plug, level gun, and perform same operation with rear filling hole. When air is all out of cylinder, tighten both plugs and elevate to five degrees, allow to stand for about five minutes, then remove front plug and again refill. Loosen drain plug and drain out about ¼-gill of oil into receptacle. Do not allow oil to run down into gun slides.

About four quarts of Hydroline oil is required to fill recoil cylinder. Oil must be clean and free from dirt and should be strained through clean linen or muslin cloth before using.

In emergencies glycerin and water, or any buffer or engine oils may be used in recoil cylinders, but should be replaced by Hydroline as soon as possible. Where the above liquids are used, all interior parts of recoil mechanism must be emptied, disassembled, thoroughly cleaned and dried before refilling.