Operating Oil Pressure

Operating oil pressure may be checked as follows:

Fill oil tank with Harley-Davidson 75 oil. Disconnect oil pressure switch wire at top of switch and remove switch. Install Oil Pressure Gauge, Part No. 96921-52. Attach gauge bracket to motorcycle and road run or simulate road running until engine is completely warmed. A full operating temperature is essential for accurate gauging. Pressure should be 25 to 28 pounds per square inch at 20 mph. At 30 mph. and over, pressure should be steady at 35 to 38 pounds.


If motorcycle is equipped with an oil filter, thoroughly wash the filter element in clean gasoline or solvent at least once every 2,000 miles when the engine oil is changed. Blow out element with compressed air before installing.

To remove the filter element, take off acorn nut, fiber washer and cup. Remove element retaining nuts and metal element retainer. Then pull element off stud. If upper metal retainer (retainer with five holes in it for oil passage) comes off with the filter element, make sure that it is reinstalled as the upper retainer when replacing the element.

Replace filter element every 5,000 miles.


All models specially equipped with large, 51 ampere hour battery are fitted with an external oil tank located to right side of battery case, under the seat. The tank is equipped with a large mouth filler opening and a screw cover. As optional equipment, this tank may be fitted with an internal oil filter (see Fig. 3A-2).

Wash filter element (3) in clean gasoline or solvent at 2,000 mile intervals, renew at 5,000 mile intervals. To service filter element, remove cap from oil tank, remove retaining spring (1) and washer (2) and pull out filter. Make certain "O" ring is positioned against filter cup flange (6) when filter is installed in tank.

SERVICING OIL TANK CAP AND FILLER OPENING. To disassemble, follow order shown in Fig. 3A-2. Assembly is reverse order of disassembly. Clean and inspect all parts. Replace any that are worn or damaged.

If oil leak should occur between the tank cap and the filler opening, with cap and gasket in serviceable condition, check the lip of the filler opening. A cap

1. Filter clip

2. Cap plain washer

3. Filter element

4. Filter lower retainer

5. Cup spring

8. Dipstick and valve assembly

9. Cap gasket

10. Cap cotter pin

11. Cap screw

12. Cap washer

13. Cap nut

14. Cap top

Figure 3A-2. Oil Tank Filter - Exploded View drawn too tight will bend the lip of the filler opening resulting in an imperfect seal between gasket and lip.

Drain oil from tank. Using a mallet as a driver and a block of wood as a cushion, bend the lip down until flush with sealing surface of tank cap. Remove nicks and rough spots with emery cloth. Flush tank before refilling.


A. Feed section of oil pump.

B. Check valve.

C. Maximum oil pressure regulating valve.

D. Front chain oiler adjusting screw.

E. Pinion gear shaft through which oil is forced to connecting rod lower bearings, from which it splashes to cylinder walls, pistons, main bearings, etc.

F. Oil screen.

G. Dripper.

> Feed oil from tank to engine. Oil is forced through passages as indicated to connecting rod lower bearings, and through oil screen (see inset) and passages in crankcase, cylinder and head walls to tappets, hydraulic lifters, rocker arms and push rods.

II > By-Pass oil. Surplus oil over and above the volume required escapes past pressure regulating valve (C) and, flows through passage indicated, discharging directly into timing gear case where it lubricates timing gears and settles into scavenger pump sump from which it is returned to tank.

Front chain oil. Oil is bled from by-pass oil for front chain lubrication through passages indicated which terminate in outside breather passage. Exhausting crankcase air delivers oil vapor to chain. Oil is regulated by adjusting screw (D).

RETURN OIL SYSTEM (Fig. 3A-4) J. Scavenge section of oil pump.

K. Timed "rotary" crankcase breather valve. Rotary breather valve is timed to open on downward stroke of pistons, allowing crankcase exhaust air to expel scavenge oil from crankcase into timing gear-case. This interval is indicated by arrows. During this interval, the small port in breather valve is closed. Rotary breather valve closes on upward stroke of pistons, creating vacuum in crankcase. During this interval, the small port in breather valve lines up with passage in crankcase. Oil is then retrieved by vacuum from outside breather oil trap (L) in crankcase as indicated by arrows. • •>

L. Outside breather oil trap.

M. Crankcase oil scavenging sump.

—► Oil returned by gravity. Oil accumulated in cylinder head cover, drains out through passages in cylinder walls and into crankcase. Oil from hydraulic push rods drains down through the push rod covers through slots in tappet guides into timing gear-case.

Scavenge oil and crankcase exhaust air from crankcase sump (M). Exhaust air expels scavenge oil from crankcase through rotary breather valve (K), into timing gear case where the oil settles into scavenger pump sump and is returned to tank.

Crankcase exhaust air. Escapes from timing gearcase through outside breather passage which terminates in front chain guard. Any oil still carried by exhaust air is trapped in outside breather oil trap (L).

• • > Oil retrieved by vacuum. As oil accumulates in outside breather oil trap (L) in crankcase, it is retrieved by crankcase vacuum through passage as indicated.

Scavenge Oil (return oil) from engine to oil tank. Oil is pumped from engine through passages as indicated.

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