The gearcase, located on the right side of the engine crankcase, contains a train of gears which transmit engine power to the cam shaft, crankcase breather, timer, oil pump and generator. The gearcase is lubricated with engine oil through the by-pass circulatory system and through the breather valve from engine crankcase.

All gear shafts run in bushings except the crankcase side of the cam shaft which operates in a needle roller bearing. The circuit breaker (timer) gear and intermediate gear turn on stationary shafts and are fitted with bronze bushings.


Before disassembling gearcase, it is advisable to remove push rods, tappets, push rod hydraulic units and tappet guides as described in "Disassembling Tappets."

Remove oil screen cap (1), gasket (2), screen body (3) or spring (3A) screen (4), and screen seal (1 or 2 used) (5). Remove screen from screen housing by rotating screen until notch in screen lines up with key in housing.

Remove 12 gearcase cover screws (6), oil passage screw (6A) with washer (6B), and two long generator fastening screws (7), and remove generator.

Remove two timer-to-motor bolts and slip timer assembly out top of gearcase.

Tap gearcase cover with wood or rawhide mallet to loosen and remove gearcase cover (8) and gearcase cover gasket (9).

Remove idler gear spacer (10) and circuit breaker gear spacer (11). Make a mark on one of the spacers to insure^ its assembly to the same gear. The spacers look identical but one may be thicker than the other.

Remove breather valve spacing washer (12).

Remove cam gear (13), spacing washer (14), and thrust washer (15).

Remove breather gear (16), circuit breaker gear (17) and idler gear (18).

Remove pinion gear shaft nut (19) which has a left-hand thread. Use Gear Shaft Nut Socket Wrench, Part No. 94555-55. Pull pinion gear (20) using Pinion Gear Puller and Installer, Part No. 96830-51 as shown in Fig. 3D-5. Tool has lefthand threads.

Remove key (21). Slip off spring (22), gear shaft pinion spacer (23), oil pump pinion shaft gear (24) and key (25).

Slip breather screen (26) and separator (27) out of pocket in gearcase.

Remove oiler drive gear shaft spring ring (28), oiler drive gear (29) and oiler drive gear key (30).

If necessary, remove oil pump stud nuts and washers and remove oil pump from gearcase. See "Disassembling Oil Pump."


Wash and air-dry all parts. Wash inside of case. If crankcase is to be disassembled, wash parts after complete disassembly. If it is not to be repaired, be careful to get no grease solvent into crankcase when washing gearcase.

Inspect oil screen (4) carefully to make sure mesh is open. Holding screen to light is not an absolute check. It is possible for oil screen to be plugged or partially plugged with tiny lint-like fibers and still permit light to pass. Replace plugged or partially plugged screen. Probe oil screen hole in gearcase with a length of wire formed to a short hook to determine if there are any additional oil screen seal gaskets (5) in hole. More than the prescribed number will block off oil feed channel when screening unit is assembled.

Inspect breather screen (26). It must be clean and unobstructed.

Inspect cam gear and pinion gear bushings (37 and 38) in gearcase cover for pitting, scuffing and grooving. Determine amount of pinion and cam shaft wear in cover bushings. If it exceeds maximum tolerance shown in "Engine Specifications," Section 3A, by .001 in., install new bushings.

Inspect circuit breaker and idler gear fit on respective shaft. Examine bushings (34, 35 and 36) and stud shaft for pitting, grooving or scuffing. If amount of wear exceeds maximum tolerance shown in "Engine Specifications" by .001 in., replace bushings and/or stud shafts (32 and 33).

Attach dial indicator to gearcase cover mounting screw hole and determine amount of pinion shaft play in right main roller bearing. When tolerance in "Engine Specifications" is exceeded by .001 in., bearings should be replaced.

Inspect needle bearing (31) for wear, broken or gouged bearings. If end of cam shaft shows any appreciable wear (.003 in. or more), needle bearing is probably worn to a point where replacement of bearingand cam shaft are advisable.

Needle bearing can be removed and installed in crankcase without disassembling crankcase with Puller Tool, Part No. 95760-69. Press needle roller bearing into crankcase with Tool, Part No. 97272-60, as shown in figure 3D-9. Press from heavier end having the manufacturer's name only. Pressing from opposite end will crush roller race and bind rollers. Push new bearing into crankcase from gearcase side. Pinion shaft main roller bearing may be replaced only when crankcase is disassembled (see "Disassembling Crankcase," Section 3E).

Figure 3D-5. Pulling Pinion Gear

Install new pinion gear shaft bushing (38) in hole in cover as follows:

Position bushing in cover so oil hole in bushing is exactly in line with lubrication channel outlet in cover. Press in bushing on arbor press until top of bushing is flush with cast bushing boss on cover. Locate and center punch new dowel pin location 1/8 in. or more from original location. Drill No. 31 hole 3/16 in. deep. Press in bushing until it bottoms on shoulder in cover boss hole. Continue drilling dowel pin hole to depth of 9/32 in. from top of bushing. Drive in new dowel pin and carefully peen edges of hole to lock pin in place.

To replace cam shaft cover bushing, proceed as follows:

Use Puller Tool, Part No. 95760-69, to extract old bushing. Make a mark on outside of bushing boss tc locate original dowel pin hole. Press in new bushing with arbor press until shoulder is against cover boss. Locate new dowel pin hole at least 1/8 in. from original hole, centerpunch and drill No. 31 hole exactly 9/32 in. deep. Drive in new dowel pin and peen bushing edges over dowel to secure it

Figure 3D-5. Pulling Pinion Gear

Inspect gears for wear. Assemble pinion and cam gears to respective positions in gearcase. Mesh is considered ideal when no play between gears can be felt and cam gear can be moved back and forth along shaft axis without restriction. Omit cam gear end spacer in assembly for purposes of this check and attach cover with at least four cover screws.


Remove pinion shaft cover bushing using Puller Tool, Part No. 95760-69 (Fig. 3D-6).

Drill lubrication oil hole through wall of bushing with 5/32 in. drill, using oil hole in bushing boss as a drill guide.

Pinion shaft and cam shaft bushings must be line reamed to remove burrs and irregularities from hole

Figure 3D-6. Removing Pinion Shaft Cover Bushing 3D-6

Figure 3D-7. Line Reaming Cover Bushing and to insure perfect alignment. If crankcase is not disassembled, use any right crankcase side. Fasten cover in place with at least four screws.

To ream pinion shaft bushing, insert reamer pilot in right crankcase roller race. Insert 9/16 in. Pinion â– Shaft Cover Bushing Reamer, Part No. 94805-57, through pilot and push into cover bushing until it bottoms (see Fig. 3D-7), then give reamer one complete turn to size bushing. Rotate reamer the same direction (clockwise) during extraction.

To ream cam gear cover bushing, insert Cam Gear Shaft Bushing Reamer, Part No. 94802-36, through needle bearing in crankcase, into cover bushing. Turn reamer until it bottoms in gearcase cover.

Bushings in circuit breaker and idler gears may be pressed out on an arbor press using a suitable drift pin, and new bushings pressed in.

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