The presence of oil leaking 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. Though the second cause is not as harmful, it can cause blowby if it is not quickly dealt with.
Things You'll Need
- Hand pump
- 5/8-inch spark plug socket
- Socket wrench
- Compression gauge
- SAE 20W-50 motorcycle-grade engine oil
- Torque wrench
Oil Level Check
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.
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 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.
Drain out the excess oil, using a hand pump, until the oil level is between the upper and lower marks on the dipstick.
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.
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 compression of 125 psi.
Remove the spark plug if the compression is less than 125 psi. Pour a half-ounce of SAE 20W-50 motorcycle-grade engine oil into the cylinder, then retest the cylinder's compression. If the compression reading increases, the piston rings and the cylinder must be overhauled because the piston can no longer maintain a seal against the cylinder wall.
Unscrew the compression gauge and place it in the rear engine cylinder. Check the cylinder's compression using the same method as for the front cylinder.
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, burning oil and fouled spark plugs.
- 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. Oil blown into the air cleaner through overfilling will eventually be pulled into the engine, where it will be burned and turn into carbon deposits on the cylinder wall. The deposits will cause excessive wear on the piston rings, creating the possibility of blowby.
- The Professional Motorcycle Repair Program: Lubrication and Cooling Systems, Volume 5; Professional Career Development Institute
- The Professional Motorcycle Repair Program: Four-Stroke Internal-Combustion Engines, Volume 5; Professional Career Development Institute
- The Professional Motorcycle Repair Program: Harley-Davidson Maintenance, Volume 23; Professional Career Development Institute
- The Professional Motorcycle Repair Program: Four-Stroke Engine Top-End Inspection, Volume 14; Professional Career Development Institute
- Harley-Davidson Service Manual: Touring Models; Harley-Davidson Motor Co.
- Photo Credit Jupiterimages/Photos.com/Getty Images
What Are the Symptoms of a Bad PCV Valve?
A PCV valve, or Positive Crankcase Ventilation valve, assists with the evacuation of gases from an internal combustion engine’s crankcase. A bad...
CVO 110 Engine Specs
The Screamin' Eagle 110 V-Twin engine is a high-torque motor used to power the Harley Davidson custom vehicle operations (CVO) Softail convertible...
Harley Davidson Oil Problems
There's a lot of allure to a Harley Davidson motorcycle, for bike enthusiasts and non-bikers. But like any bike or motor vehicle,...
How to Repair Engine Oil Leak
A lot of engine oil leaks can be stopped without the need of a skilled mechanic. 5 to 30 minutes of your...
How to Clean a Harley Davidson Air Cleaner
Harley-Davidson, a motorcycle manufacturer in the United States, has a rich history with its first motorcycle being built in 1903 in Milwaukee,...
How to Fix a Primary Oil Leak on a Harley
Harley-Davidson motorcycles use a chain-driven primary system to transmit power from the engine sprocket to the clutch housing. Drive plates in the...
How to Change a Harley-Davidson EFI Fuel Filter
With each mile traveled on a Harley-Davidson, dirt and grime enter the engine and could eventually cause motor problems. This is why...
How to Fix a Harley Davidson Oil Leak
The name Harley Davidson is synonymous with motorcycles, a desert landscape, street cool and rebelliousness. Some famous riders include actors Brigitte Bardot,...
How to Prime a Harley Oil Pump
Replacement Harley oil pumps must be primed after installation but before their first use in order to prevent “air lock” or cavitation....
How to Stop Engine Oil in an Air Breather
The crankcase air breather is opposite the PCV valve on the engine to allow air flow to enter the positive crankcase ventilation...
How to Troubleshoot High PSI in the Oil Tank on a Harley
There are four likely causes that an oil gauge on a Harley might indicate high oil pressure. Two of the causes are...
Harley Davidson Troubleshooting Guide
Harley-Davidson is an American motorcycle manufacturer founded in Wisconsin in 1903. Although Harley-Davidson's are known for being well-engineered, like any machine they...
About Slobbering Oil Problems in a Harley Davidson
In a Harley Davidson motorcycle, slobbering oil, also known as oil carryover, is a common problem caused by deteriorated, cracked or improperly...
Harley-Davidson Air Shocks Troubleshooting
Harley-Davidson equipped their touring models with adjustable rear-air shocks and adjustable front-air forks standard from the factory. You can control the suspension...