Volkswagen Air Cooled 1949-1969 Repair Guide

Engine Mechanical Troubleshooting

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Fig. Fig. 1 Trouble Engine Misfiring



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Fig. Fig. 2 Shooting Lack of Power

The accompanying engine diagnosis chart, is a flow diagram presentation of the logic involved in tracking down problems within the engine and narrowing down the field of possible engine ailments. The following engine conditions and possible causes should also prove helpful to the troubleshooter:

ENGINE WILL NOT START

The following are possible reasons why the engine will not start. Eliminate them one at a time.

  1. Battery is weak.
  2.  
  3. Coil or condenser is faulty.
  4.  
  5. Cracked or shorted ignition cables.
  6.  
  7. Defective starter motor.
  8.  
  9. Starter solenoid defective.
  10.  
  11. Moisture contained in distributor cap.
  12.  
  13. Battery connections loose or corroded.
  14.  
  15. Blockage of fuel line.
  16.  
  17. Carburetor float setting incorrect.
  18.  
  19. Fuel pump inoperative.
  20.  
  21. Dirt in carburetor, blocking needle valve or jet.
  22.  
  23. Carburetor flooded due to extended starting attempts.
  24.  
  25. Distributor contact points dirty.
  26.  
  27. Ignition timing incorrect.
  28.  
  29. Spark plugs improperly gapped.
  30.  

ENGINE MISSES DURING ACCELERATION

The following are possible reasons why the engine misses during acceleration. Eliminate them one at a time until the problem is discovered.

  1. Ignition timing incorrect.
  2.  
  3. Spark plugs dirty or improperly gapped.
  4.  
  5. Faulty carburetor accelerator pump.
  6.  
  7. Distributor contact points dirty or burned.
  8.  
  9. Engine valves burned or warped.
  10.  
  11. Carburetor improperly adjusted.
  12.  
  13. Ignition coil or condenser faulty.
  14.  
  15. Distributor advance mechanism inoperative.
  16.  

ENGINE MISSES AT HIGH SPEEDS

The following are possible reasons why the engine misses at high speeds. Eliminate them one at a time until the problem is discovered.

  1. Dirt in fuel line or carburetor.
  2.  
  3. Ignition timing incorrect.
  4.  
  5. Excessive play in distributor shaft.
  6.  
  7. Distributor cam or rotor burned or worn.
  8.  
  9. Ignition points incorrectly gapped.
  10.  
  11. Inoperative ignition coil or condenser.
  12.  

ENGINE EXHIBITS POOR PERFORMANCE

AT ALL SPEEDS

The following are possible reasons why the engine exhibits poor performance at all speeds. Eliminate them one at a time until the problem is discovered.

  1. Ignition timing incorrect.
  2.  
  3. Ignition coil or condenser faulty.
  4.  
  5. Excessive play in distributor shaft.
  6.  
  7. Distributor shaft cam worn.
  8.  
  9. Malfunctioning of distributor advance mechanism.
  10.  
  11. Spark plugs dirty or incorrectly gapped.
  12.  
  13. Compression low or unbalanced in different cylinders.
  14.  
  15. Ignition cables cracked and shorting out.
  16.  
  17. Engine valves burned, warped, or pitted.
  18.  
  19. Carburetor float setting incorrect.
  20.  
  21. Fuel line or carburetor blocked by dirt.
  22.  
  23. Excessive back pressure in exhaust system due to clogged muffler or tail pipe.
  24.  
  25. Valve timing incorrect.
  26.  
  27. Leaky intake manifold or carburetor gasket.
  28.  
  29. Carburetor out of adjustment or broken.
  30.  

ENGINE STALLS

The following are possible reasons why the engine stalls. Eliminate them one at a time until the problem is discovered.

  1. Incorrect idle speed setting.
  2.  
  3. Choke adjustment incorrect.
  4.  
  5. Improper slow-speed mixture setting in carburetor.
  6.  
  7. Coil or condenser faulty.
  8.  
  9. Distributor points dirty or incorrectly gapped.
  10.  
  11. Carburetor float setting incorrect.
  12.  
  13. Leaky intake manifold or carburetor gasket.
  14.  
  15. Ignition wiring faulty.
  16.  

LOW OIL PRESSURE

The following are possible reasons why the engine exhibits low oil pressure. Eliminate them one at a time until the problem is discovered.

  1. Oil thin or diluted.
  2.  
  3. Oil level too low.
  4.  
  5. Oil pump worn or not operating properly.
  6.  
  7. Bearing clearances excessive.
  8.  
  9. Oil pressure sending unit inoperative.
  10.  
  11. Oil pressure relief valve sticking.
  12.  
  13. Obstruction in oil pump suction tube.
  14.  

ENGINE NOISES
Valve

The following are possible reasons why the engine is making valve noises. Eliminate them one at a time until the problem is discovered.

  1. Sticky valves.
  2.  
  3. Bent valve stem.
  4.  
  5. Warped or burned valve head.
  6.  
  7. Valve spring broken.
  8.  
  9. Valve tappets out of adjustment.
  10.  
  11. Loose rocker arms.
  12.  
  13. Bent or worn pushrod.
  14.  
  15. Worn or loose rocker arm shaft.
  16.  
  17. Worn valve or tappet guides.
  18.  
  19. Tappets dirty.
  20.  
  21. Valve springs of wrong specifications.
  22.  

Piston

The following are possible reasons why the engine is making piston noises. Eliminate them one at a time until the problem is discovered.

  1. Piston collapsed or broken.
  2.  
  3. Piston pin too tight.
  4.  
  5. Excessive clearance between piston and cylinder.
  6.  
  7. Piston or cylinder wall scored.
  8.  
  9. Broken piston rings.
  10.  
  11. Loose or broken piston pin.
  12.  
  13. Misalignment of piston and cylinder bore.
  14.  

Crankshaft Bearing

The following are possible reasons why the engine is making crankshaft bearing noises. Eliminate them one at a time until the problem is discovered.

  1. Loose connecting rod bearing.
  2.  
  3. Main bearing loose.
  4.  
  5. Connecting rod bent.
  6.  
  7. Flywheel loose.
  8.  
  9. Excessive crankshaft end-play (noticeable when engaging clutch).
  10.  
  11. Loose crankshaft pulley. (Sounds like bearing.)
  12.  
  13. Crankshaft misalignment.
  14.  

Detonation

The following are possible reasons why the engine is producing detonation noises. Eliminate them one at a time until the problem is discovered.

Detonation is a spontaneous combustion within the cylinder. It is caused by an imbalance of compression ratio, heat, fuel value, and timing. Detonation can be annoying, wasteful and also destructive to engine parts.

  1. Excessively high engine temperature.
  2.  
  3. Spark plugs that are too hot for their intended use.
  4.  
  5. Improper ignition timing.
  6.  
  7. Use of a fuel of a too low octane rating.
  8.  
  9. Carburetor mixture excessively lean.
  10.  
  11. Incandescence within the combustion area caused by carbon particles, sharp edges, burnt spark plugs, etc.
  12.  

 
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