The gearcase, located on the right side of the engine crank-case. contains a train of gears which transmit engine power to the camshaft and circuit breaker, crankcase breather and oil pump. The gearcase is lubricated with engine oil through the bypass circulatory system and through the breather valve from engine crankcase.

Shafts run in bushings except the crankcase side of the camshaft which operates in a needle roller bearing.


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

1. Remove oil screen cap (1), O-ring (2), screen spring (3) and screen (4).

2. Remove two circuit breaker cover screws (5), cover (6) and gasket (7) from gearcase cover (17).

3. Remove circuit breaker cam assembly bolt (8). Remove screws (9, 9A or 9B), lockwashers and washers (10) or retainer (10A) and circuit breaker plate assembly (11).

4. Remove circuit breaker cam (12) and circuit breaker advance assembly (13)

5. Remove gearcase cover screws (14, 15 and 16).

6. Tap gearcase cover with wood or rawhide mallet to loosen and remove gear cover (17 or 17A) and gearcase cover gasket (18 or 18A). Note that 1973 and later parts are different than earlier parts and must not be interchanged.

7. Remove breather valve spacing washer (19) and breather gear (20).

8. Remove cam gear (21), spacing washer (22), and thrust washer (23).

9. Remove pinion gear shaft nut (24) which has a lefthand thread. Use Gear Shaft Nut Socket Wrench, Part No. 94555-55. Pull pinion gear (25) using Pinion Gear Puller and Installer, Part No. 96830-51 as shown in Figure 3-30. Tool has lefthand threads.

10. Remove key (26), gear shaft pinion spacer (27), oil pump pinion shaft gear (28) and key (29).

11. Use a lock ring pliers such as Snap-On No. PR129A, and remove oil pump drive gear shaft lock ring (30), drive gear (31) and drive gear key (32).

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


1. 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 not to get any grease or solvent into crankcase when washing gear-case.

2. 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.

3. Inspect cam gear and pinion gear bushings (33 and 34) in gearcase cover for pitting, scuffing and grooving. Determine amount of pinion and camshaft wear in cover bushings. If it exceeds maximum tolerance shown in "Engine Specifications," by .001 in., install new bushings.

4. Inspect cam gear oil seal (35) in cover to see that lip is in good condition.

5. 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.

6. Inspect needle bearing (36) for wear, broken or gouged bearings. If end of camshaft shows any appreciable wear (.003 in. or more), needle bearing is probably worn to a point where replacement of bearing and camshaft are advisable.

7. Needle bearing can be removed and installed in crankcase without disassembling crankcase with Puller Tool, Part No. 95760-69 as shown in Figure 3-34. Press needle roller bearing into crankcase with Tool, Part No. 97272-60 as shown in Figure 3-34. Press from heavier end having the manufacturer's name only. Pressing from opposite end will crush roller race and bind rollers. Pinion shaft main roller bearing may be replaced only when crankcase is disassembled (see "Disassembling Crankcase.")

8. Inspect gears for wear. Assemble pinion and cam gear to respective positions in gearcase. Omit cam gear end spacer in assembly for purposes of this check and attach cover with at least three cover screws. 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.

1. Oil screen cap

3. Oil screen spring

4. Oil screen

5. Circuit breaker cover screws (2)

6. Circuit breaker cover

7. Circuit breaker cover gasket

8. Circuit breaker cam assy, bolt

9. Circuit breaker plate screw (2) (1970)

9A. Circuit breaker plate screw (1971 to 1972) 9B. Circuit breaker plate screw (late 1972 8c later)

10. Circuit breaker plate screw lockwasher and washer (1970)

10A. Retainer (1971 to early 1972)

11. Circuit breaker plate assy.

12. Circuit breaker cam

13. Circuit breaker advance assy.

17. Gear cover (1970-72) 17A. Gear cover (1973 & later)

18. Gear cover gasket (1970-72) 18A. Gear cover gasket (1973 & later)

19. Breather gear washer

20. Breather gear

21. Cam gear

22. Cam gear spacing washer

23. Cam gear thrust washer

24. Gear shaft nut

25. Pinion gear (early 1977 & earlier) 25A. Pinion gear (late 1977 & later)

26. Pinion gear key

27. Pinion gear spacer

28. Oil pump pinion shaft gear

29. Oil pump pinion shaft gear key

30. Oil pump drive gear lock ring

31. Oil pump drive gear

32. Oil pump drive gear key

33. Gear cover camshaft bushing

34. Gear cover pinion shaft bushing

35. Camshaft oil seal

36. Camshaft needle bearing

38. Wire clip

39. Welch plug

40. Oil line fitting

41. Oil pump shaft

Figure 3-30. Pulling Pinion Gear


Remove pinion shaft cover bushing using Puller Tool, Part No. 95760-69 as shown in Figure 3-31.

Install new pinion gear shaft bushing (34) in hole in cover as follows:

Position bushing in cover so oil hole or flat 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. Note that on 1973 and later models, flat on bushing must line up with oil hole in cover.

Figure 3-31. Removing Pinion Shaft Cover Bushing

To replace camshaft cover bushing (33), proceed as follows:

Use Puller Tool, Part No. 95760-69, to extract old bushing. Make a mark on outside of bushing boss to 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.

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 camshaft bushings must be line reamed to remove burrs and irregularities from hole and to ensure perfect alignment. If crankcase is not disassembled, use another right crankcase side. Fasten cover in place with al least three screws.

To ream pinion shaft bushing, insert reamer pilot in righl crankcase roller race as shown in Figure 3-32. Insert 9/16 in. Pinion Shaft Cover Bushing Reamer, Part No. 94805-57 through pilot and push into cover bushing until it bottoms. then give reamer one complete turn to size bushing.

Rotate reamer the same direction (clockwise) during extraction.

To ream cam gear cover bushing, use a 1 in. expansion reamer and ream to 1.003/1.002 in. diameter.

Figure 3-32. Line Reaming Cover Bushing
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