Replacing Mechanical Fuel Pumps: A Guide For Small Block Chevys

Changing the mechanical fuel pump on an SBC engine can be a challenging task, but with the right tools and guidance, it is certainly achievable. The fuel pump is located on the passenger side front corner of the engine, in front of the motor mount. Before beginning the process, it is important to note that the fuel line may be pressurized, so one should be prepared to handle any leaking fuel safely. The first step is to remove the metal fuel line using a line wrench, followed by the rubber fuel line. It is crucial not to bend the metal line to avoid installation issues later on. Next, the fuel pump flange bolts need to be loosened and removed, taking care not to fully remove one bolt before the other. The fuel pump backing plate should then be taken out to access the fuel pump push rod, which tends to slide down behind the plate. After removing the old pump, the push rod needs to be cleaned and coated with grease to prevent it from falling out. The new fuel pump can then be installed, ensuring the metal fuel line is aligned with the pump fitting. The rubber fuel lines are reconnected, and the flare nut is started by hand, being cautious not to cross-thread the fitting. With the new fuel pump in place, the engine can be started, relying on the residual fuel in the injectors or carburetor.

Removing the fuel pump

To remove the fuel pump on a small-block Chevy engine, you'll need to first locate the fuel pump on the passenger side front corner of the engine, in front of the motor mount.

Supplies

Before you begin, gather the following supplies:

• 5/8" line wrench
• Rag
• Socket
• Ratchet
• Extension
• Grease
• Solvent
• Gasket adhesive
• Automotive silicone

• Use the 5/8" line wrench to remove the metal fuel line. Wrap a rag around the wrench to catch any leaking fuel.
• Remove the rubber fuel line from the pump and plug the line to prevent leaks.
• Use the socket, ratchet, and extension to remove the fuel pump flange bolts. Loosen both bolts, then alternate between them until they are out.
• Remove the fuel pump backing plate to access the fuel pump push rod.
• Clean the parts, including the fuel pump cavity, with a solvent.
• Coat the fuel pump push rod with grease to prevent it from falling out.

Once the fuel pump is removed, you can install a new gasket and fuel pump, ensuring everything is properly aligned and tightened before starting the engine.

Removing the fuel pump mounting plate and gasket

To remove the fuel pump mounting plate and gasket, you will need to first remove the bolts holding the fuel pump in place. The bolts on the fuel pump flange are typically 7/16", but it's not uncommon for them to be 9/16" if they have been replaced. Be sure to loosen both bolts before removing either, and alternate between them to avoid misaligning the plate.

Once the fuel pump is removed, you can then take out the fuel pump pushrod, which will have fallen or slid down behind the fuel pump backing plate. This can be a tricky process, and you may need to use a magnetic pick-up tool or needle-nose pliers to retrieve it. If you're really struggling, you can remove the backing plate to access the pushrod more easily.

With the pushrod removed, you can now take off the mounting plate and gasket. Be sure to clean any remaining gasket from the engine block and backing plate, and also wipe out the fuel pump pushrod cavity with a rag to remove any excess oil.

Preparing for fuel leakage

Changing the mechanical fuel pump on an SBC engine can be a tricky process, and it is important to be prepared for any potential fuel leaks that may occur. Here are some detailed instructions to help you prepare for fuel leakage when undertaking this task:

Before beginning the process of changing the mechanical fuel pump, it is crucial to ensure that you have the necessary tools and safety equipment. This includes eye protection, gloves, and a fire extinguisher. It is also recommended to have a helper to assist with the process and to ensure that the area around the vehicle is clear of any flammable materials or potential sources of ignition.

The next step is to relieve the pressure in the fuel system. This is an important safety precaution as it helps to reduce the risk of fuel leakage and the potential for injury. Ensure that the engine is off and cold, and then locate the fuse panel. Remove the fuel pump fuse to disable the fuel pump, and then turn the ignition key to the 'on' position for about two seconds. Repeat this process a few times to relieve the pressure in the fuel lines.

Once the pressure is relieved, you can proceed to disconnect the fuel lines from the fuel pump. Place a clean rag or towel around the connection to catch any spilled fuel. Carefully loosen the fittings and disconnect the lines, being mindful of any residual pressure or fuel that may be present. It is important to work slowly and carefully during this step to minimize the risk of fuel leakage.

After the fuel lines are disconnected, you can remove the old fuel pump. Again, be cautious of any residual fuel that may be present in the pump or lines. Place the old fuel pump in a safe container for proper disposal.

At this stage, it is important to inspect the fuel lines, fittings, and the area around the pump for any signs of damage or leaks. Check the rubber hoses for any cracks, wear, or deterioration. If there is any damage, it is crucial to replace the affected parts to prevent fuel leaks. Ensure that all connections are secure and tight to prevent leakage.

Finally, before installing the new fuel pump, take the time to clean the mounting surface and ensure that it is free of any debris or residue. This will help ensure a proper seal and reduce the risk of fuel leakage. Follow the manufacturer's instructions for installing the new fuel pump, ensuring that all connections are secure and all components are properly aligned.

By following these steps and being cautious of potential fuel leaks, you can help ensure a safer and more successful mechanical fuel pump replacement on your SBC engine.

Removing the rubber fuel line

To remove the rubber fuel line from the pump, you will first need to wrap a rag around the wrench and flare nut to capture any leaking fuel. This is because the motor may have been running recently, meaning the fuel line is pressurized with fuel. Do not smoke and ensure no one nearby is welding or using a flame.

Next, use a 5/8" "line" wrench to remove the metal fuel line. For most classic Chevy small block fuel pumps, the line wrench used to remove the flare nut would be 1/2". Once the flare nut is removed, slide it back, but do not pull the metal line out of the fuel pump fitting. If you force it out, the metal line could bend, and you will have difficulty starting the threads when it is time to reinstall the new fuel pump.

Now, remove the rubber fuel line from the pump. Plug the fuel line with something to prevent it from leaking fuel. You can use the butt end of a drill bit for this. The check valves in the fuel pump should prevent the pump from draining fuel onto the floor. The fuel supply line can be 5/16" or 3/8".

Finally, use a socket, ratchet, and extension to remove the fuel pump flange bolts. The bolts on this fuel pump are 7/16", but it is not uncommon for someone to replace the factory bolts, so you may find bolt heads of 9/16" instead. The bolt size is a 3/8" course thread. Do not remove one bolt entirely and then the other; loosen both bolts, then alternate between them until they are out.

Installing the new fuel pump

Before installing the new fuel pump, it is important to clean the parts. Use a thick grease to lightly coat the fuel pump push rod. This grease will prevent the rod from falling out when released. Insert the push rod into the hole until it touches the cam shaft—it should not be forced further with a hammer. Next, clean any remaining gasket from the engine block and the fuel pump backing plate.

Glue the new gasket to the back of the fuel pump backing plate. A suitable adhesive is "yellow death" or weatherstripping adhesive. Ensure all parts are grease-free before applying the glue. After gluing the gasket, place a very thin layer of automotive silicone on the gasket surface. Put the fuel pump backing plate in place on the engine block and start all four bolts in their respective holes.

Tighten the two small bolts at the bottom of the fuel pump backing plate, then remove the two fuel pump bolts. By starting all the bolts before tightening, you ensure the fuel pump backing plate is properly aligned. Next, glue the new gasket onto the fuel pump and apply a thin layer of automotive silicone on the gasket. Put the fuel pump bolts in the fuel pump flange bolt holes.

Place a spot of grease on the end of the fuel pump arm and position the fuel pump, ensuring the metal fuel line is aligned with the fuel pump fitting. Hold the pump in place while starting the threads on each of the fuel pump bolts. Keep the pump upright, preventing the fuel pump arm from slipping off the end of the fuel pump push rod. Once the fuel pump bolts are started, alternate between them, tightening each a few turns until they are snug. Tighten them to approximately 25 ft/lbs.

A fine bead of silicone should squeeze out from around the fuel pump and fuel pump backing plate. Finally, replace the rubber fuel lines and start the flare nut by hand. You may need to wiggle the metal line to get the flare nut threads to start. Push the fuel line straight into the fuel pump fitting to centre it, making the flare nut easier to start. Do not use a wrench to start the flare nut, as this may cause cross-threading.

Frequently asked questions