oil breather leaking
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brofactor
- Rookie
- Posts: 2
- Joined: Mon Mar 21, 2011 2:02 pm
- Real Name: Harry
- Sex: Male
- Years Riding: 40
- My Motorcycle: 1990 harley FLHTC-U
oil breather leaking
Just started up my 1990 Harley flhtc-u for the first time this season and found oil leaking out of the oil breather filter on the underside of the bike. Any thoughts on why this happening ?
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Gummiente
- Site Supporter - Platinum
- Posts: 3485
- Joined: Wed May 11, 2005 11:34 pm
- Real Name: Mike
- Sex: Male
- Years Riding: 38
- My Motorcycle: 03 Super Glide
- Location: Kingston, ON
Re: oil breather leaking
Welcome to TMW!
Harleys have a dry sump system that stores the oil in a tank separate from the motor. Because this tank is higher than the motor, a one-way check valve is installed in the oil return line coming from the crankcase so that oil can't drain back into it once the motor is shut off and the oil pressure drops to zero. However, these check valves sometimes get stuck open a bit by a small piece of dirt and then the oil WILL leak from the tank down into the crankcase. It's a very small leak, but over long periods of time it can add up. Then when the bike is started, the excess oil will be whipped into a pressurised foam by the crankshaft and much of it will exit the engine via the oil breather filter. My guess is this is what has happened to your bike.
Harleys have a dry sump system that stores the oil in a tank separate from the motor. Because this tank is higher than the motor, a one-way check valve is installed in the oil return line coming from the crankcase so that oil can't drain back into it once the motor is shut off and the oil pressure drops to zero. However, these check valves sometimes get stuck open a bit by a small piece of dirt and then the oil WILL leak from the tank down into the crankcase. It's a very small leak, but over long periods of time it can add up. Then when the bike is started, the excess oil will be whipped into a pressurised foam by the crankshaft and much of it will exit the engine via the oil breather filter. My guess is this is what has happened to your bike.
Mike 
It isn't WHAT you ride,
It's THAT you ride
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brofactor
- Rookie
- Posts: 2
- Joined: Mon Mar 21, 2011 2:02 pm
- Real Name: Harry
- Sex: Male
- Years Riding: 40
- My Motorcycle: 1990 harley FLHTC-U
Re: oil breather leaking
makes sence, hopefully after I change the oil and get it ready for the season it will be corrected. Thank you