Full Guide On Where & Why Harleys Leak Oil: This tech explains

When a Harley leaks oil, it marks its spot. We’ve all heard this and many still believe the saying. I spoke with a long time motorcycle tech and here is what he had to say on the topic.

Why Do Harley’s Leak Oil?

Like any vehicle, a motorcycle can leak oil. The root cause can be just about anything.

Generally speaking, Harleys leak oil from the primary cover located on the left handsome of the motorcycle because of bad seals or o-rings. They can also leak oil from the drain plug and starter areas. Because some Harleys have external oil lines, these can also be common places for oil leaks. 

Yes, that was a blanket answer to the question why do Harley’s leak oil. But you need to know there is no direct answer one can apply to the WHY question.

The only thing we can do is talk about larger trends and quality control.

Speaking of quality control, we can look back to the period in time when Harley’s “marked their spot” with an oil leak on the showroom floor. 

Quality Control Leading To Harley Oil Leaks

The quality of the bikes was not as high as it is today. If you are a Harley fan, you know this took place during some of the dark years of Harley’s history. I will spare you the details but know that AMF did nothing to help make the bikes better.

During recent years, Harley did make a recall of some 57,000 bikes due to an oil line coming loose. I can tell you from experience working with the oil lines on a Harley is not something I enjoy. 

More Seals and O-Rings May Create More Leaks for Harley

Because of the way Harleys are made, there are generally more seals and o-rings on them than you would find on other manufacturers. This creates potential areas for leaks to develops.

I can tell you from personal experience. My Harley has had a few small leaks with the seals being the biggest cause. They were not hard to fix but Harleys seem to have more of them than other brands.

Other manufactures generally make the transmission part of the engine housing, whereas Harley separates the two components. 

Common Harley Models that Leak Oil

As I already alluded, the many of the older models of Harley use to mark thier spot on the showroom floor. The stereotyping did not seem to be associate with any one particular model.

Curiosity got the better of me so I spend sometime going through forums and various other items to discover an interesting take on the topic of Harley models that leak oil.

It seems from this post on Quora, a contributor gives a little history on the reason Harleys leaked as a means to lubricate the primary chain. You can read the post for yourself, but I think it goes a little beyond this explanation. As we already know, there are other places that oil leaks happen.

Looking at the more recent history of Harley, we know in 2017 many of the touring models had a voluntary recall due to an malfunction with an oil line. Here is the list of bikes:

  • Road Glide Special
  • Street Glide Special
  • Electra Glide Ultra Classic
  • Road King Classic
  • Road King
  • Road Glide
  • Street Glide
  • Road King Special

Also if you look hard enough, you find every model will have an out outlier bike. What do I mean by this?

No manufacturer can build with 100% quality. There will be a few individual bikes here or there with leaks or failures of some kind. The problem comes when we go looking for something to justify a bias we already have.

Do all Shovelheads leak oil?

We have all heard it and read jokes online about it. “Harley’s mark their spot with an oil drip.” Unfortunately, this reputation has not completely left the brand.

The Shovelhead engine was the curator of the image that all Harley’s leak oil. Worn head gaskets, valve cover gaskets, and oil pump seals are common places for these engines to leak. Leaks on brand new motorcycles from 1966 to 1984 (primarily the AMF years) were from poor quality control. Rebuilding shovelhead engines with modern techniques reduce the likelihood of an oil leak.

Common Oil Leaks For The Shovelhead

As I noted earlier in the post, any engine at any point in time may develop a leak. When you look at the numbers on a large scale, the shovelhead engine had a few common places it would leak.

A worn engine may leak at the head or valve cover gaskets. The oil pump was another commonplace for them to leak. While digging on a few forums of the years, I have come across several mentions of oil lines leaking. 

On the face of it, it sounds like many places for the black gold to ooze from the big twin. It has kept me from even considering any Harley from this era. 

Increased Harley Leaks During AMF Period

See AMF purchased Harley in 1969. Harley was not doing very well, so the partnership with AMF was a glimmer of hope to improve the brand and the bike.

The problem was AMF had its hands in everything and knew little about what the brand needed to improve. As a result, the quality of the bike declined to a worse state than before the partnership with AMF.

Applying Modern Techniques to the Shovelhead

With the advancement of technology and improved machining techniques, the quality of a rebuild Shovelhead engine reduces the likelihood of seeing an oil leak.

Perhaps this improved process is an upgrade in quality control. They would be correct, but the modern techniques we use today were not common in the 70s and early 80s.

Finding A Harley Oil Leak

So far we have spend time talking about why your Harley is leaking. Now it time to talk about how to find it.

On the surface of the discuss, finding an oil leak should be easy work. However, you may find it can actually be harder than you think.

For example, the first time I changed the oil in my primary. I had bought the wrong gasket for my clutch cover. Of course I did not know this at the time.

After taking the bike on the bike on a 20 mile ride, I noticed a small drip from the bottom side of my primary on the left hand side of the bike. It looked like the oil was dripping from the plug.

I tightened the plug just a smidge and went on down the road.

This happed a few times on the next 3 rides. I final wised up to what I had done. I did not catch the oil coming from the clutch cover gasket because the film of oil was so thin and clear because it was new.

Here is a great process from a popular Harley tech on how to find your oil leak.

Harley Leaking Oil After Sitting

We have to revisit a comment I made earlier in the post. Harley motorcycles have three different compartments for oil: the engine, the primary, and the transmission.

Because Harley motorcycles have three different compartments, there will be more seals and o-rings on the engine when compared to other motorcycle brands. This increases the chance of a leak after sitting. After a Harley has been sitting for a while, seals may dry up and shrink, leaving small gas between adjacent motor components creating small leaks (aka cold leak) or drip.

There is nothing more aggravating than coming out to your garage and finding oil drips below your motorcycle. This has happened to me with a few of the motorcycles I’ve owned over the years. 

You look to see if you can find the leak’s origin. 

If you’re like me, you’re eager to go on a ride, so you clean up the oil, go for a ride and come back to find the bike has stopped leaking. 

Why was it leaking while sitting and then stopping suddenly once I rode it?

The answer lies in two stages:

  1. The engine gaskets likely dried up some while sitting and left small gaps between the engine components it sealed. When this happens, oil finds its way into these gaps and will drip out of the bike. Once the bike runs again, the gaskets absorb oil, expand and seal up the gaps. Think of it like a sponge drying up after you wash dishes. It shrivels until you get it wet again.
  2. Once the engine components get warm, the metals expand, closing the gap between them. 

Between both items, the small gaps come close up and stop oil leaks. 

You should not believe that every leak that develops after sitting is from a cold engine. You could have a cracked housing somewhere.

Make sure you look to find the origin of the leak. Not doing so could make the problem worse. 

Harley Leaking Oil At Head

Let explore your Harley leaking oil around the head.

Take a look a the picture below of the motor.

Notice where the head starts and the cylinder ends. You may be noticing oil coming from this part of the V-twin.

There is a thin gasket in there that has failed. Any number of items could have affected it causing your problem.

The question is what do you do about it now? Should you ride the bike?

The obvious answer is to get it fixed. Depending on how the leak is, you may not want to ride it down the road.

Think about it. If you’re dripping oil on the road right in front of your back tire, it will create the perfect condition for an accident. So yeah, you should probably not ride it unless the leak is tiny.

How much does it cost to replace a head gasket on a Harley?

Harley Leaking Oil At Brether

While researching another oil leak, I came across a recurring mention of oil coming out of the breather of Harleys.

Generally, Harleys made before the 1990s have a higher chance of leaking oil out of the breather than models made afterward. Oil coming out of the breather tube may be an indication the air cleaner is dirty and needs to be cleaned as quickly as possible. Air cleaner leaks may also indicate a problem deeper inside the engine. 

How did oil leaks from the breather start?

Believe it or not, leaks from the breather were intentional from some vehicles and it did not start with Harley. Farm equipment frequently leaked oil all over the place. Just look at old tractors and farm equipment and you will see what I mean.

These old pieces of machinery pushed lubricant outside of the internal working components to help lubricate different parts. As a result, oil and grease dripped everywhere.

Harley’s were not much different from farm equipment. They had oil dripping on the chain to keep it lubricated. Air moving through the inner engine saturated with oil. 

As some of this internal air made its way out of the engine through the breather tube, oil would leak from it.

Depending on the severity of the leak, though, it could show a problem deeper in the motor. I am not an expert on older Harleys and would suggest you connect with a Harley tech if you have specific questions.

Harley Oil Breather Leak Fix

It seems there are three fixes for oil coming out of your older Harley (provided it is not a bigger problem):

  1. Put a special filter on the breather tube. This will let the air escape, but keep the oil in the motor.
  2. Check your air cleaner. When it is dirty, it can make the engine push oil out of the breather. 
  3. Get a modern carburetor on your bike that runs the breather tube to the inner part of the carb. This allows the oil to circulate back through the motor and combust with the rest of the fuel.

Can you ride a motorcycle with a oil leak?

Someone is always willing to ride just about any motorcycle, no matter its condition. The question should be, should they?

As a general rule, people should not ride a motorcycle with oil leaks that could put them in danger of having an accident. Small leaks that do not drip on the roadway (such as from the head) in front of a tire will not create a problem in the short run. Make every attempt to fix the leak. Novice riders should avoid riding a motorcycle with any oil leak.

When oil drips from the engine onto the roadway, you run the chance of the back tire running over the oil. Doing this long enough will reduce the friction on the back tire, making it slick and hard to ride. An accident will occur.

Gauging an oil leak to determine if you should ride the bike can be hard and comes with many years of riding and working on motorcycles. New riders are at risk the most with oil leaks and should avoid riding when a leak develops.

The leak should be fixed. 

Perhaps you are thinking, “This is ridiculous, I’ve ridden my motorcycle many times with an oil leak and nothing happened.”

While you may have gotten by with those many rides, we all know what happens with oil leaks. They get worse. Then it eventually becomes an issue.

Why chance it? Just fix the leak and get back on the road.

Steps For Locating the Oil Leak

The best way to look for your oil is to watch the video below. It is one of the best ways to approach this task.

There is not much I could add to so here you go.

Now stop reading and get out there for a ride or spin some wrenches on that motorcycle.


Bosco is a long time motorcycle rider with 30+ years of experience. After his childhood ATV accident and becoming a father, motorcycle safety has become his focus.

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