Clearance Space: Pan-Pickup Tube Relationship

Ensuring sufficient clearance between the oil pump and oil pan is critical when building an engine. The clearance between the oil pickup tube and the oil pan can vary depending on the specific engine and application. A common rule of thumb is to maintain a clearance of between 3/8 and 1/2, although some applications may require more or less clearance. It is important to measure the clearance accurately and make any necessary adjustments to ensure optimal engine performance and avoid issues such as oil starvation or vortex formation.

How to measure the clearance between the oil pump and oil pan

Measuring the clearance between the oil pump and oil pan is critical to ensure sufficient clearance and oil pressure while the engine is in operation. Here is a step-by-step guide on how to measure the clearance:

• Prepare the Oil Pan and Pickup Tube: Gather the oil pan, pan gasket, and oil pump pickup tube. If the pickup tube is already installed, remove it temporarily for accurate measurement. Clean the mating surfaces of the oil pan and engine block to ensure no debris interferes with the measurement.
• Mark the Pickup Tube: Use a thin piece of tape, such as racer's tape, on the end of the pickup tube to prevent any foreign material from entering the tube during the measurement process. Then, apply a small amount of clay or modelling clay to the end of the pickup tube. The clay should be soft enough to deform easily but not too sticky.
• Dry-Fit the Oil Pan: Dry-fit the oil pan to the engine block without applying any sealant or gasket. Ensure the pan is snugly fitted at all corners. You may need to loosely attach the pan with bolts to hold it in place.
• Measure the Clay Thickness: Remove the oil pan from the engine block. Carefully examine the clay on the pickup tube. Use a pair of calipers to measure the thickness of the clay. This thickness will give you the clearance between the oil pump and oil pan.
• Consider the Gasket Thickness: If you're using a gasket, remember to account for its thickness. Remove the clay from the pickup tube and place the gasket in position. Reattach the oil pan and measure the clearance again using the clay method. This will give you an accurate measurement that includes the gasket thickness.
• Alternative Method with a Straightedge: Lay a straightedge on the pickup screen and measure its distance from the block rail on both sides. Then, place the straightedge across the rear of the oil pan and measure the depth of the sump. Also, measure the thickness of the gasket. These measurements will help you determine the total clearance.
• Adjust Clearance if Needed: If the clearance is outside the recommended range, you may need to adjust the pickup tube. Gently tap the tube with a soft-faced hammer to bend it slightly, checking for the desired clearance after each adjustment. Be careful not to flatten the tube or damage the pickup screen.
• Final Assembly: Once you've achieved the desired clearance, proceed with the final assembly. Install the gasket and oil pan according to the manufacturer's instructions. Ensure all fasteners are tightened to the specified torque values.

It is important to note that the recommended clearance between the oil pump and oil pan can vary depending on the application. A general rule of thumb is to maintain a clearance between 3/8" and 1/2". However, always refer to the engine manufacturer's specifications or consult with an expert for the optimal clearance for your specific engine.

Minimum clearance between the oil pan and the pickup

When installing an oil pan, it is important to ensure that there is sufficient clearance between the pan and the oil pickup tube to prevent issues such as reduced oil volume and oil starvation. The recommended clearance varies depending on the vehicle's specific engine and oil pan design, but generally ranges from 1/4" to 3/8".

For a dirt track engine with a high-pressure pump, it is recommended to have a minimum of 1/4" clearance, with a preferred range of 1/4" to 3/8". This measurement can be obtained by calculating the difference between the internal pan depth and the distance from the block's pan rails to the pickup bottom. It is also suggested to add a small stop or bump at half the height to prevent the pan or tube from flexing and causing contact.

For a Ford 429 CJ engine with a stock CJ pan and pump, the recommended clearance is between 3/16" and 1/4", but some suggest a minimum of 1/4" and a maximum of 3/8". It is important to consider the thickness of the oil pan gasket, which can add approximately 1/16" to the overall clearance.

In the case of a Small Block Chevy engine, the recommended clearance is 5/16" to 3/8". This clearance helps to reduce windage horsepower loss and provides quicker drain back for oil thrown from the crankshaft at high RPM.

For a Melling Select HV pump with a 9-1/4" deep oil pan, a custom pickup tube assembly may be required to achieve the desired clearance. In this case, the pickup tube was cut and shortened by 0.485", resulting in a clearance of approximately 3/8".

It is important to note that having insufficient clearance can lead to issues such as reduced oil volume and oil starvation, while too much clearance can cause the oil to "see" an insufficient level, resulting in potential issues with oil pressure and lubrication.

How to adjust the clearance between the oil pan and the pickup

The consensus across various forums is that the ideal clearance between the oil pan and the pickup is between 0.25 and 0.5 inches. This measurement is important to ensure that the pickup does not come into contact with the oil pan, which can lead to engine damage.

• Bending the Pickup Tube: One common method is to gently bend the pickup tube away from the oil pan using a soft-faced hammer. Hold on to the pickup while gently tapping the tube halfway to the pump. This should move the tube by around 0.25 inches without flattening it.
• Using a Spacer: If the oil pan has a very flexible bottom, using a spacer between the sump and the pickup is recommended. This will prevent the sump from being sucked into the pickup due to suction.
• Welding a Bolt: For a more solid solution, some people weld a bolt, head-end down, to the pickup to ensure it does not lose clearance. This can help prevent issues when running over objects on the track.
• Adjusting the Gasket: The thickness of the gasket between the oil pan and the engine block can also affect the clearance. Thicker gaskets will increase the distance between the oil pan and the pickup.
• Modifying the Oil Pump: In some cases, it may be necessary to modify the oil pump itself. However, this should be a last resort as it can affect the oil pump drive height and cause clearance issues with the crankshaft.

It is important to note that the clearance between the oil pan and the pickup can affect oil pressure and the chance of air being induced into the oiling system. Therefore, it is crucial to find the right balance and ensure that the clearance is within the recommended range.

The impact of clearance on oil pressure and engine performance

The clearance between the oil pan and the pickup tube is essential for optimal engine performance and longevity. The distance between the two components plays a critical role in maintaining the oil wedge, a protective lubrication layer that ensures smooth rotation, reduces wear, and enables efficient force transmission.

The recommended clearance between the oil pan and the pickup tube varies across different applications and engine designs. A general rule of thumb is to maintain a distance of 3/8" to 1/2", with a minimum clearance of 1/4" suggested by some experts. However, it is important to note that a closer distance to the oil pan is generally preferable as it reduces the amount of unusable oil.

On the other hand, tighter clearances result in increased resistance to oil flow, leading to higher oil pressure. This can provide more uniform loads and oil pressure on the bearings. Tighter clearances also require less oil to maintain the hydrodynamic wedge, reducing the load on the oil pump and potentially increasing horsepower. However, a thinner film of oil between the bearing and journal can lead to higher temperatures, which may be less of a concern in racing engines but can increase wear in daily-driven vehicles.

The choice between looser and tighter clearances depends on the specific performance goals and engine applications. Looser clearances are often preferred for improved oil cooling and lower oil temperatures, while tighter clearances are chosen for more uniform load distribution and consistent oil pressure. Additionally, the viscosity of the oil used also plays a crucial role, with thinner oils supporting tighter clearances and thicker oils requiring looser clearances.

In summary, the clearance between the oil pan and the pickup tube has a significant impact on oil pressure and engine performance. A careful balance between clearance and oil viscosity is essential for maintaining optimal oil pressure and ensuring the efficient functioning of the engine.

Recommended clearance for different types of oil pans and pumps

When installing an oil pan, it is important to measure the clearance between the oil pump and the oil pan to ensure sufficient clearance and oil pressure while the engine is in operation. The recommended clearance for all pans is 5/16"-3/8", with some sources recommending a minimum of 1/4" clearance. This measurement can be calculated by measuring the internal pan depth and the distance from the block's pan rails to the pickup bottom, then taking the difference between the two measurements. Gaskets will add some additional clearance.

For deep sump pan pickups, which are submerged deeper into the oil, the clearance can be up to 1/2". This is because deep sump pan pickups are less sensitive to clearances.

It is important to note that too much clearance can lead to a pressure loss, while too little clearance can make the pickup inefficient. Therefore, it is crucial to get the correct clearance for the specific oil pan and pump being used.

When choosing an oil pump, it is important to pick one that suits the oil-pressure demands of the engine and its intended use. For example, a high-volume oil pump is recommended for vehicles with an oil cooler, remote filter, or extra-capacity oil pan. On the other hand, a standard-volume oil pump may be sufficient for drag racing or street/strip cars with a stock-capacity oil pan.

Additionally, the type of oil pan can also impact the performance of the oiling system. Dry-sump oil pans are popular in forms of racing where low chassis height is important, as they provide increased capacity, improved scavenging, and more consistent oil pressure. Wet-sump systems, on the other hand, are generally better suited for street applications and most exotic and high-performance street cars.

Frequently asked questions