How to Troubleshoot an Oil Leak in the Air Cleaner of a Harley Davidson

Maintain the proper oil level to avoid damaing your Harley-Davidson's engine.

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The presence of oil leaking out from your Harley-Davidson's air cleaner is the first symptom of a condition called "blowby", which allows the pressure generated within the engine's combustion chamber to blow past the pistons. This pressure forces oil out of the engine crankcase and into the air cleaner. Blowby affects the engine's ability to compress air and fuel to create the combustive force needed to operate. However, a similar oil leak can occur if the motorcycle's oil tank is overfilled. While the second cause is not as harmful, it can cause blowby if it is not quickly dealt with.

Related Searches:Difficulty:Moderately ChallengingInstructions Things You'll NeedHand pump5/8-inch spark plug socketSocket wrenchCompression gaugeSAE 20W-50 motorcycle-grade engine oilTorque wrenchSuggest EditsOil Level Check1

Start the engine and let it idle in place for three minutes to allow the engine oil to warm in the oil tank. Stop the engine, then let the oil settle for five minutes.

2

Check the oil level, using the dipstick attached to the oil tank. If the oil level is above the upper mark on the dipstick, the oil tank is overfilled. The oil tank has a vent tube that leads into the engine crankcase, where it will eventually be blown into the air cleaner through a separate breather tube.

3

Drain out the excess oil, using a hand pump, until the oil level is situated between the upper and lower marks on the dipstick.

Compression Testing1

Remove the spark plugs from both engine cylinders, using a 5/8-inch spark plug socket and a socket wrench. Push the spark plugs into the spark plug cables, then ground the spark plug electrodes against the engine cylinders to avoid damaging the ignition coil.

2

Screw a compression gauge into the front cylinder spark plug hole. Twist the throttle grip into a completely open position. Turn the ignition on and press the starter button to build up pressure in the front cylinder. Release the starter button once the compression gauge needle no longer moves. Ideally, the gauge should indicate a minimum of compression of 125 psi. Remove the spark plug and pour a half-ounce of SAE 20W-50 motorcycle-grade engine oil into the cylinder then retest the cylinder's compression, if the cylinder compression is less than 125 psi.

If the compression reading increases, the piston rings and the cylinder must be overhauled since the piston can no longer maintain a seal against the cylinder wall.

3

Unscrew the compression gauge and place it in the rear engine cylinder. Check the cylinder's compression, using the same method.

4

Screw the spark plugs into the engine cylinders and tighten them to 18 foot-pounds, using a torque wrench.

Tips & Warnings

A loss of compression in one or both engine cylinders will show other symptoms as well, including a loss of power, oil-burning and spark plug fouling.

Do not operate the motorcycle's starter without grounding the spark plugs against the engine or the motorcycle's frame. Turning the engine over without grounding the spark plugs will damage the motorcycle's ignition system.

Keep the oil level below the dipstick's upper mark to avoid the possibility of excess oil to be pulled into the engine and out into the air cleaner. Oil blown into the air cleaner through overfilling will eventually be pulled into the engine, where it will be burnt and turn into carbon deposits on the cylinder wall. The deposits will cause excessive wear on the piston rings, creating the possibility of blowby.

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ReferencesThe Professional Motorcycle Repair Program: Lubrication and Cooling Systems, Volume 5; Professional Career Development InstituteThe Professional Motorcycle Repair Program: Four-Stroke Internal-Combustion Engines, Volume 5; Professional Career Development InstituteThe Professional Motorcycle Repair Program: Harley-Davidson Maintenance, Volume 23; Professional Career Development InstituteThe Professional Motorcycle Repair Program: Four-Stroke Engine Top-End Inspection, Volume 14; Professional Career Development InstituteHarley-Davidson Service Manual: Touring Models; Harley-Davidson Motor CompanyResourcesMotorcycle Cruiser: Understanding Blow-By in Motorcycle EnginesPhoto Credit Jupiterimages/Photos.com/Getty ImagesRead Next:

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