Service Information On Hydraulic Type Push Rods With Which All 1948 Overhead Valve Engines Are Fitted

Here is complete service information on hydraulic type push rods applying to all 1948 overhead valve model engines.

The instructions which follow under the heading, "Push Rods and Valve Tappets' will be published in the new Rider's Instruction Book now being printed. As you will note from these instructions, riders will be told tappets of these engines do not require periodic adjustment and no information is given riders about adjusting tappets nor hydraulic push rods.

The instructions given under the heading, "Adjusting Tappets of 1 94 8 Overhead Valve Engines, Which Are Equipped with Hydraulic Type Push Rods" explain how to make this adjustment when necessary, and the instructions under the heading "Servicing Hydraulic Push Rod" explain servicing procedure. These instructions are intended for and are being sent only to pur dealers for their own use and for the use of their mechanics.

NOTE: Since the Rider's Instruction Folders which are being included with new motorcycles until the new books are ready, make no reference to the 1948 hydraulic type push rods and tappets, it will be well for you to pass along to those who purchase 1948 overhead valve models in the meantime, the rider information contained in this bulletin.


Push rods are self adjusting, hydraulic type. They automatically adjust their length to compensate for hot engine expansion and valve mechanism wear, and thus keep the valve mechanism free of lash when engine is running. Tappet adjustment is required only in new engine assembly, and when engine is reassembled after repair, to compress the push rod hydraulic units to the length specified for normal functioning. No further readjustment of tappets is required.

On starting an engine, which has been shut off even for a few minutes, the valve mechanism may tend to be slightly noisy until the hydraulic push rod units completely refill with oil. If at any time, other than for a short period immediately after engine is started, valve mechanism becomes abnormally noisy, it is an indication that one or more of the hydraulic push rod units may not be functioning properly. Always check the lubricating oil supply in the oil tank first, if the valve mechanism becomes noisy, since normal circulation of oil through the engine is necessary for proper operation of the hydraulic units. If there is oil in the tank, the push rod units may not be functioning properly due to contamination in the oil supply. Drive at moderate speed to the nearest Harley-Davidson Service Station for further attention.

ADJUSTING TAPPETS OF 1948 OVERHEAD VALVE ENGINES (Dealer and Mechanic Information)

Engine must be cold.

Remove push rod cover keepers and telescope covers to expose tappets.

Before readjusting a tappet, make sure it is at its lowest position. You can make sure of this by turning engine in the direction in which it runs until the like tappet (intake or exhaust) in the other cylinder is at its highest position (valve fully open).

Loosen tappet adjusting screw lock nut and turn tappet screw down until push rod is free and has noticeable shake. When checking for push rod shake, grasp push rod with finger tips just below cylinder head, and shake toward front and rear of engine.

Slowly turn tappet screw upward just far enough to take up all push rod shake. Now, mark tappet screw with chalk or in some other manner, so its turns can be accurately counted, and then continue turning it upward exactly three full additional turns.

Adjust the other three tappets the same way.

With tappets accurately adjusted according to above instructions, hydraulic units will be compressed 3/32" which is the specified setting for normal functioning.

If, after readjusting tappets, engine does not start readily because of loss of compression in one or both cylinders, allow engine to stand a few minutes before further attempt to start. This standing time is required to allow the newly adjusted hydraulic units time to leak-down until valves are fully seated.

Bear in mind that after initial tappet adjustn ent as described above, hydraulic type push rods are self-adjusting to compensate for hot engine expansion and valve mechanism wear. Therefore, tappet adjustment is normally required only in new engine assembly and when engine is reassembled after having been taken apart for repair.

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