How to Check and Change Primary Oil on Your Harley-Davidson

You might not give changing the main oil in your Harley much thought, but it is crucial. Even though used motor oil may permanently harm your engine, many riders often put off getting their oil changed. You would believe that changing the main oil is difficult, but it’s actually a rather simple job that just needs some basic tools and no specialised experience.

Motorcycles have less complicated technology, smaller engines, and fewer parts than vehicles, making maintenance considerably quicker and simpler. Because it’s quick and simple, changing your primary oil is the ideal task to practise your mechanical skills. So set aside some time for your ride and let’s get started!

The Tools You Require

There are a few tools you need before you start this process. You’ll require

  • An aperture.
  • Any container that can hold the liquid, such as drain pans.
  • Fresh O-ring.
  • A 5/8-hole.
  • A torque bit T27.
  • An impact wrench.
  • A torque tool.
  • A main cover gasket, if necessary.
  • The ideal motor oil for your engine’s needs.

Keep your service handbook close by as well. The majority of oil changes use these tools, although your service handbook may list additional ones if necessary; this is unusual.

You should also always get the primary fluid that is recommended in your service handbook. Every bike has a unique set of requirements, therefore you can’t just buy any main fluid. This might seriously affect how well your motorbike works and result in unpleasant problems like oil burning, gasket damage, and other things.


How to Check and Change Primary Oil


To successfully change the primary oil in your Harley, you need the right tools and knowledge. Follow these steps for a smooth and efficient oil change:

  1. Preheat Your Engine: Before starting the oil change process, it’s recommended to warm up your bike’s engine. Simply switch on your motorcycle and let it run for a few minutes. This step ensures the primary oil is heated, enabling smoother flow and uniform distribution throughout the engine.

Some service manuals suggest reaching the ideal operating temperature by riding your bike for at least 30 minutes beforehand. If feasible, follow this guideline. However, if time is limited, ensure the engine is adequately heated to facilitate easier oil drainage and prevent oil residue from causing engine issues.

  1. Ensure a Clean Engine Area: Maintaining a clean and grime-free bike is essential. After preheating the engine, elevate your motorcycle using a jack or stand for better stability during the oil change process.

Take a cloth and thoroughly clean the engine area, paying special attention to the drain case and drain plug. While there’s no need for intensive cleaning with chemicals or other materials, ensure a dirt-free working space by gently wiping the surfaces.

By following these steps, you can optimize the process of changing the primary oil in your Harley. Remember, a clean engine area and a preheated engine contribute to a seamless oil change experience and better overall performance of your motorcycle.


The location of the drain stopper is the first stage in this procedure. The primary drain plug secures the oil and stops leaks. The drain stopper is positioned beneath the principal drain case, as the name implies.

It shouldn’t take you long to locate the drain case because it isn’t difficult to find. Your service handbook contains useful information if you can’t find it.


After finding the primary drain case, remove the drain case’s bolts with your socket wrench and T-27 torque bit. Your Harley will typically have five of these bolts. Keep these bolts secure once you remove them since you’ll need them to reassemble the drain case.

Remove the lid and set it aside after removing the bolts. You are now prepared to empty your main fluid.


It’s best to put on a pair of gloves before draining the main fluid. If primary fluid gets on your skin, getting it off might be a little challenging.

Now, remove the primary drain plug with your socket wrench and 5/8-inch socket. Place the drain container beneath the stopper once it is free enough to be rotated by hand. Allow the primary oil to drain out after completely removing the stopper.

Make careful to drain the oil completely. Let gravity handle this; it can take a while.



The previous primary case gasket may become worn out after prolonged operation. It would be great if you got a new one. If you see any leaking or gasket damage, remove the old gasket from the main case lid.

Take your new gasket and set it on the lid after that. The gasket in the main case has a groove designed for it; the replacement gasket will slide directly into that groove. This should be done while the major fluid drains since it will save you time and help you finish the task more quickly.


Prior to reinserting the drain plug, always clean it. The plug may now be examined to see whether it is suitable for usage in the future. As you examine and clean the drain plug, take a look at the old O-ring too.

The O-ring should be replaced following each primary oil change, according to the majority of service manuals. Therefore, before doing a main oil change, make sure you have purchased a new O-ring.

Take the replacement O-ring and put it in the drain plug the same way you did before.


Fit the drain plug back in after replacing the O-ring and cleaning the drain plug. Starting by hand, insert the plugs, then use your socket wrench and 5/8 inch socket to fully tighten them.

Take your torque wrench and set it to fourteen to twenty one foot pounds of torque once you have tightened the drain plug. Next, use the torque wrench to tighten the drain plug.


For this stage, you need the funnel. A funnel designed exclusively for first-time cases is available for purchase. The majority of bike funnels are globally compatible, so you may use one instead.

Take your oil and use your funnel to pour it into the intake at this point. Keep in mind that you must add the precise amount of main oil that is called for in your service manual. One quart of primary fluid, for instance, is needed in the case of a Harley Davidson Softail.
Read your service handbook to determine how much main oil your Harley requires; if you go over this amount, you’ll likely end up damaging gaskets due to the increased internal pressure brought on by too much oil.

After you’ve poured the oil, be careful to visually check the fluid level again because most motorbike engines have a designated sweet spot.

What is the primary oil capacity?

Don’t worry about how many oz it is or if it does not match the manual, just fill the primary case to the point that it says it is full, usually just up to the bottom of the clutch spring when the bike is upright and level.

Installing the Primary Case Cover and the Importance of Primary Oil

Once you’ve added the necessary primary fluid, it’s time to securely place the primary cover back on. Follow these steps for a smooth installation process:

1. Prepare the Bolts:
Before proceeding, ensure you have the bolts ready for installation. You’ll need to hold the case in position while tightening each bolt into its designated hole.

2. Secure the Bolts:
Begin by hand-tightening the bolts and then use a T-27 torque wrench and socket wrench to snugly fit them in. Set your torque wrench to the recommended 84-108 inch-pounds of torque. Tighten all the bolts securely into their respective holes.

With the primary cover correctly installed, you’re all set!

Understanding the Significance of Primary Oil:

Primary oil is vital for the proper functioning and longevity of your Harley. It serves several critical purposes:

1. Lubrication of Bike Parts:
Primary oil circulates throughout your engine, effectively lubricating all its components. This lubrication minimizes friction between metal parts, preventing engine seizure and reducing damage caused by wear and tear.

2. Enhanced Fuel Efficiency:
When primary oil effectively reduces friction within the engine, the combustion process becomes more efficient. As a result, less fuel is consumed, optimizing your bike’s fuel efficiency. Conversely, increased friction leads to higher power requirements, reducing gas mileage.

3. Prolonged Lifespan of Engine Components:
The metal components within the engine require proper lubrication to prevent excessive friction and subsequent wear. Primary oil forms a protective layer on these parts, significantly reducing friction and heat generation. This preservation of internal components increases their lifespan, preventing premature deterioration.

By following the correct installation procedure for the primary case cover and maintaining a high-quality primary oil, you can ensure optimal performance and longevity for your motorcycle’s engine. Regularly check and change the primary oil to uphold the smooth operation of your Harley.

4. How Frequently Should You Replace Your Bike’s Primary Fluid?

From bike to bike, it varies. To find out how often you should change your primary oil, carefully read your service handbook. Typically, you should replace the main fluid every 2500 to 3500 miles of riding; consult your owner’s handbook for the precise mileage range.
Remember that these figures might change based on the weather and the condition of the engine of your motorbike.

5. What is the primary oil capacity of the Twin cam 88?

It ought to require a quart (950 ml; 32 fl oz).

A 1988 twin cam requires what kind of oil?

For their Twin Cam engine, Harley Davidson recommends that you always use 20W-50 full-synthetic oil. You can utilise the same oil for Transmission and Primary.


This job sounds more difficult than it is. You may always have your main oil changed at a professional. But keep in mind that changing your main oil is really easy and takes very little time or effort. You shouldn’t see your mechanic for a straightforward procedure that you can complete at home. An effective approach to hone your mechanical skills is to change the oil in your Harley. So go ahead and replace the main oil in your Harley Davidson by following these instructions.

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