Repair And Diagnostic Procedure


When an engine needs repair, it is not always possible to definitely determine beforehand whether the engine can be repaired by disassembling only cylinders and heads, only gearcase; or whether engine must be completely disassembled for crankcase section repair.

Usually, only upper-end repair is needed and it is recommended procedure to first strip motorcycle for cylinder head, cylinder and piston repair as described in "Stripping Motorcycle for Engine Repair," steps 1 through 9. After disassembling cylinder head and cylinder it may be found that lower end repair is necessary. This re-quires removal of engine crankcase from frame as de scribed in steps 10 through 16 in "Stripping Motorcycle for Engine Repair."

In cases where it has been definitely determined beforehand that the lower portion of engine (crankcase) is in need of repair, remove complete engine from chassis before starting disassembly as described in steps 1 through 16 of "Stripping Motorcycle for Engine Repair."

Symptoms indicating a need for engine repair are often misleading, but generally if more than one symptom is

Lubrication System

1978 Shovelhead Primary Starter Bushing

present, possmie symptom causes can De narrowea down to make at least a partial trouble diagnosis. An above normal consumption of oil, for example, could be caused by several mechanical faults (see "Locating Troubles," Section 1). But when accompanied by a blue-gray smoke from the exhaust, and when low compression is present, it indicates the rings need replacing. Low compression by itself, however, indicates improperly seated valves, not worn rings.

A noisy engine is usually caused by loose bearings. Main bearings are generally more durable than rod bearings or bushings so the latter should be suspected first. Certain "knocking" noises may be caused by loose bearings, others by piston slap, a condition where piston or cylinder or both are worn out of round and loose fitting, allowing the piston slap from front to rear of cylinder as it moves up and down.

inspect vaive stems tor scurring ana cnecK stem to guide clearance. Check vaive seats for signs of looseness or shifting.

7. Grind valves and valve seats. COMPRESSION TESTING PROCEDURE

Satisfactory engine performance depends upon a mechanically sound engine. In many cases, unsatisfactory performance is caused by combustion chamber leakage. A compression test can help determine the source of cylinder leakage. Use a compression tester such as the Sun model UTC-48 that has a screw-in type adapter.

A proper compression test should be performed with the engine at normal operating temperature when possible. Proceed as follows:

Most frequently, valves, rings, pins, bushings and bearings need attention at about the same time. If the symp-tons can be narrowed down through the process of elimination to indicate any one of the above components is worn, it is best to give attention to all of the cylinder head and cylinder parts.


To diagnose and correct noisy hydraulic lifters and valve train components, use the following procedures:

1. With engine and oil at normal operating temperature, check oil pressure at 3000 rpm. If oil pressure is above 50 psi or below 5 psi, inspect oil pump, crankcase passages and oil hoses for restrictions or blockage. Repair or replace parts as necessary.

2. With engine running, raise push rod cover at the noisy lifter and check to see that oil is reaching the tappet. If oil is not reaching the tappet, inspect the passages in the tappet, tappet block and right crankcase for restrictions or blockage.

If oil is reaching the tappet, remove the hydraulic unit and inspect per procedure listed under "Valve Tappets and Guides." Clean tappet bore of all foreign material.

Replace hydraulic unit if necessary.

1. Disconnect spark plug wires, clean around plug base and remove plugs.

2. Connect compression tester to front cylinder per manufacturer's instructions.

3. Make sure transmission is in neutral. With choke and carburetor throttle plates in wide open position, crank engine continuously until 5 to 7 full compression strokes are completed.

CAUTION — Before starting engine, after the test, make sure that throttle plate is in the closed position.

4. Note gauge readings at the end of the first and last compression strokes. Record test results.

5. Repeat steps 2 through 4 on rear cylinder.

6. If the final readings are 100 psi or more and if the final readings do not indicate more than a 10 psi variance between cylinders, compression is considered normal. If compression does not meet specifications, see diagnostic chart below.

7. Inject approximately 1/2 oz. of SAE 30 oil into each cylinder and repeat the compression tests on both cylinders. Readings that are considerably higher during the second test indicate worn piston rings.

3. Examine push rod, hydraulic unit, tappet and tappet block for proper fits and any signs of unusual wear. Replace parts as necessary.

4. Visually inspect camshaft lobes for abnormal wear.

5. Remove camshaft and pinion gear, clean and inspect for wear and fit. Measure pitch diameters and check for out of round condition. Replace parts as necessary.

6. Remove cylinder head and rocker box assemblies. Check rocker arm end play and check for binding.


Test Results

Ring Trouble

Compression low on first stroke, tends to build up on the following strokes but does not reach normal. Improves considerably when oil is added to cylinder.

Valve Trouble

Compression low on first stroke, does not build up much on following strokes. Does not improve considerably with the addition of oil. Check tappet adjustment.

Head Gasket Leak

Same reaction as valve trouble.


The cylinder leakage test will pinpoint engine problems including leaking valves, worn, broken or stuck piston rings and blown head gaskets. The cylinder leakage tester applies compressed air to the cylinder at a controlled pressure and volume and measure the percent of leakage from the cylinder.

Use a cylinder leakage tester such as the Sun, model CLT-228 or equivalent. Follow the specific instructions supplied with the tester.

The following are some general instructions that apply to Harley-Davidson V-twin engines:

1. Run engine until it reaches normal operating temperature.

2. Stop engine. Clean dirt from around spark plugs and remove the spark plugs.

3. Remove the air cleaner and set the carburetor choke and throttle in the wide open position.

4. Remove the timing inspection plug from the crankcase.

5. The piston in the cylinder being tested must be at top dead center during the test.

6. To keep the engine from turning over when air pressure is applied to the cylinder, engage transmission in fourth gear and lock the rear brake.

7. Following the manufacturer's instructions, perform a cylinder leakage test on the front cylinder. Make a note of the percent leakage.

8. Listen for air leaks at carburetor intake, tailpipe, head gasket and timing inspection hole. Air escaping through carburetor indicates leaking intake valve. Air escaping through exhaust pipe indicates leaking exhaust valve. Air escaping through timing inspection hole indicates leaking, worn or broken piston rings, worn piston and/or cylinder. Listen around head gasket area to checking for leaking gasket.

NOTE: If air is escaping through valves check valve adjustment.

9. Repeat procedure on rear cylinder.

CAUTION — Make sure throttle plate is in the closed position before starting engine.



Perform Compression or Cylinder Leakage Test as described previously. If further testing is needed proceed as follows:

1. Remove one clutch cover screw and Install Vacuum Gauge, Part No. 96950-68.

2. Start engine and let idle, gauge snouia reau aiu n inches of water minimum.

3. Pinch chaincase vent line (3/8 in. hose running from primary case to tee). Gauge reading should be 25 inches of water minimum at 1500-2000 rpm.

4. If chaincase vacuum is low, check for leaks by pressurizing chaincase with compressed air.

CAUTION — Use 10 psi pressure maximum for leak test. Before applying air pressure through the clutch cover screw hole pinch all oil lines running to chaincase near case.

5. With chaincase pressurized, listen for leaks at following locations:

— All gasket surfaces

— Hose fittings

— Oil seals (between engine and chaincase and transmission and chaincase)

— Solenoid mounting

— Starter drive mounting

— Clutch cover seal

— Chain inspection cover seal

If primary chaincase vacuum is within specifications and the Compression and Cylinder Leakage Tests show no problems, the oil supply to the heads can be blocked to determine if the oil consumption/smoking is due to a problem in the cylinder head area.


The oil supply to the cylinder heads should not be blocked for an excessive amount of time (2 minutes maximum) or damage will result. Do not run the engine above idle speed while oil supply is blocked.

1. With engine at normal operating temperature, block off the overhead oil supply line to the cylinder heads.

2. Start engine and let idle for no more than 2 minutes. If the smoking stops during this period the problem is in the cylinder head area.

3. Remove suspect head(s) and inspect the following:

— Gasket surface of both head and cylinder

— Oil return passages for clogging

— Cylinder head casting porosity allowing oil to drain into combustion chamber

— Valve guide to valve stem clearance

— Check that lip on top of cylinder does not con tact combustion chamber. To check this, place head on cylinder without gasket. The head gasket surface must contact the cylinder gasket surface all the way around.


Use the following procedure to strip the motorcycle for either cylinder head and cylinder removal for repair with engine in chassis, or for engine removal for complete overhaul.


Disconnect battery cables (negative cable first) before performing the following steps to avoid accidental start-up of vehicle and possible personal injury.

1. Remove seat.

2. Drain gas tank. Disconnect fuel line and remove gas tank.

3. To remove instrument cover take out mounting base center screw and pry off cover side plate located at trip mileage set screw.

4. Remove upper cylinder head bracket. Note washer(s) between bracket and frame lug, use same washer(s) when bracket is assembled.

5. Remove spark plugs to avoid damaging.

6. Remove air cleaner cover, filter element, air cleaner back plate and air cleaner back plate support bracket from carburetor body.

7. Disconnect throttle and choke controls from carburetor. Remove carburetor.

8. Remove carburetor intake manifold clamps.

9. Remove exhaust pipes.

At this stage, the cylinder heads and cylinders may be removed.

To remove engine crankcase or complete engine, continue stripping motorcycle as follows:

10. Remove pivot bolt from left foot board and swing rear end of foot board down away from chain case cover. Remove chain case cover. Remove compensating sprocket shaft nut.

Remove clutch and sprocket assemblies as described in "Disassembling Clutch," Section 4.

11. Remove four bolts, attaching inner chain housing to engine.

Loosen the 4 bolts attaching the primary to the transmission.

Remove chain oiler hose at oil pump. Remove other hoses from connections at back of inner primary housing.

Remove starter, starter housing and inner primary housing.

Remove alternator rotor using puller tool, Part No. 95960-52A. See "Alternator," Section 5.

12. Disconnect timer wires at coil or connector. Disconnect alternator plug from crankcase and remove rectifier/regulator.

13. Remove footboard rear stud nut from inside of frame member and front footboard mounting stud bolts from brake master cylinder by removing nut and lockwasher on back side. Remove brake master cylinder attaching stud bolt which passes through master cylinder and frame with a lockwasher and nut on back side of frame member. Remove brake master cylinder sideplate bolt located behind master cylinder plunger boot. Swing master cylinder and sideplate assembly down away from engine crankcase. For FX models, remove footrest, brake, pedal assembly.

14. Remove exhaust system.

15. Disconnect wire from oil pressure switch. Drain oil tank and remove oil lines from oil pump. Remove crankcase breather pipe.

16. Remove two front and two rear engine mounting bolts. Engine is now completely stripped and may be removed from right side of motorcycle.

Assembly is essentially the reverse order of disassembly.

1. Install engine in chassis. Tighten mounting bolts to 35-40 ft-lbs torque.

2. Loosen transmission mounting bolts.

3. Install new O-ring on crankcase.

4. Check inner primary housing bearing. Replace if necessary using Harley-Davidson "Stud and Bearing Mount," Part No. 99626-77 in bearing recess. Install new oil seal.

5. Connect chain case hose and install inner primary case on transmission mainshaft.

6. Loosely assemble chain case mounting bolts (finger tight) to crankcase.

7. On 1978 to 1979 models, install chain housing four nuts on transmission studs and tighten to 30-35 ft-lbs torque. On 1980 models, install two nuts and two bolts. Do not tighten yet.

8. Tighten chain case to engine mounting bolts to 18-22 ft-lbs torque. Install new safety wire on chain case to engine two rear mounting bolts.

9. Tighten transmission mounting nuts to 18-22 ft-lbs torque. Make sure transmission mainshaft turns freely.

10. Tighten the inner primary case to transmission mounting bolts to 18-22 ft-lbs torque.

11. Install starter motor and housing.

12. Install clutch, compensating sprocket, primary chain and chain adjuster.

13. Install chain case cover, using a new gasket.

14. Assemble remainder of components in reverse order of disassembly.


After reassembly, chain housing must be airtight. Check using Vacuum Gauge, Part No. 96950-68. Remove one of the four screws securing the front chain inspection cover and in its place screw in the threaded fitting of the gauge. Then, with engine idling check gauge tc see that there is a reading indicating 9-11 inches water minimum. Perform check with vent hose vacuum pinched closed with a pliers between inner primary and tee fitting. The reading should now be 25 inches ol water or more. A lower reading indicates an air leak intc chain housing either at gasket, solenoid, starter shaft oi hoses.

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  • Olivia
    How big around are rod bearings on a 1978 shovelhead?
    3 years ago

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