1 Piece Fuel Pump Eccentric: The Complete Guide to Installation, Benefits, and Why It Matters for Your Engine
If you are rebuilding a carbureted small block Ford or any engine that relies on a mechanical fuel pump, the 1 piece fuel pump eccentric is the simplest, most reliable solution for driving your fuel pump. Unlike the older two-piece designs that require extra parts and careful alignment, a 1 piece eccentric mounts directly to the camshaft sprocket with a single bolt and a longer dowel pin, eliminating the risk of the outer ring slipping or wearing unevenly. This design is standard on most Ford Performance Parts crate engines and is the preferred choice for builders who want durability, minimal vibration, and a straightforward installation process.
What Is a 1 Piece Fuel Pump Eccentric?
A fuel pump eccentric is a small, offset lobe mounted on the front of the camshaft. As the camshaft rotates, the eccentric pushes against the fuel pump's lever arm, creating the reciprocating motion that draws fuel from the tank and delivers it to the carburetor.
The 1 piece eccentric is exactly what it sounds like: a single, solid piece of steel or cast iron with a mounting hole and an offset profile. It is typically used on engines that have a camshaft sprocket with a machined-in spacer, meaning you do not need a separate spacer ring. This design is found on many small block Ford engines from the early 1960s through about 1972, as well as on most modern Ford Racing crate engines.
By contrast, a 2 piece eccentric consists of an inner hub and an outer ring that spins freely. The outer ring is intended to reduce wear on the fuel pump arm, but it can also cause issues if the ring becomes loose, wears unevenly, or fails to spin properly.
Why Choose a 1 Piece Eccentric Over a 2 Piece?
The 1 piece design offers several clear advantages:
1. Durability and Reliability – A 1 piece eccentric is made from a single billet of heat-treated steel or cast iron. There are no moving parts to wear out, and no outer ring that can seize or wobble. This makes it the go-to choice for high-performance engines that see sustained high RPM operation.
2. Simpler Installation – With a 1 piece eccentric, you simply slide it onto the camshaft sprocket, align the dowel pin hole, and bolt it down. There is no need to assemble an inner hub and outer ring, and no risk of the outer ring rubbing against the timing cover.
3. Better Concentricity – Because the entire eccentric is machined as one piece, the offset is perfectly centered. This means the fuel pump lever moves in a consistent, predictable arc, which translates to more stable fuel pressure and less wear on the pump arm.
4. Compatibility with Modern Timing Sets – Many aftermarket roller timing sets, such as those from Cloyes and COMP Cams, are designed to work with a 1 piece eccentric. If your engine originally used a two-piece eccentric and a short dowel pin, you can switch to a 1 piece by simply removing the old dowel pin and pressing in a longer one.
Which Engines Use a 1 Piece Fuel Pump Eccentric?
The 1 piece eccentric is most commonly found on:
- Ford small block engines (289, 302, 351W) built from the early 1960s through approximately 1972. After that, Ford switched to a Cleveland-style two-piece design.
- Ford Performance Parts crate engines (e.g., M-6007-X302, M-6007-X351W) that are set up for a mechanical fuel pump. These engines come with a 1 piece eccentric already installed.
- Chrysler LA small block engines (273, 318, 340, 360) also use a 1 piece cast iron eccentric.
If you are converting a late-model Ford 5.0L roller engine from EFI to carburetion, you will need to install a 1 piece eccentric because the original EFI engine did not have one.
How to Install a 1 Piece Fuel Pump Eccentric
Installing a 1 piece eccentric is a straightforward job that you can do during a timing set replacement. Here is the step-by-step process:
Step 1: Prepare the Engine – Remove the harmonic balancer, timing cover, and old timing set. Clean all mounting surfaces thoroughly. Debris can cause the chain and sprockets to wear out quickly.
Step 2: Install the Dowel Pin – If your engine originally used a two-piece eccentric and a short dowel pin, remove the old pin. Press the new, longer dowel pin into the camshaft until it is fully seated. The longer pin will extend through the eccentric and into the sprocket to provide proper alignment.
Step 3: Align the Engine – Rotate the crankshaft until the number one piston is at top dead center. The crankshaft key should be pointing straight up. Rotate the camshaft until the dowel pin is pointing straight down. This ensures the timing marks will align correctly.
Step 4: Assemble the Timing Set – Loop the timing chain over the camshaft sprocket, then align the timing marks on both sprockets. Slide the sprocket and chain assembly onto the crankshaft and camshaft. Make sure both sprockets are fully seated.
Step 5: Install the Eccentric – Slide the 1 piece eccentric onto the camshaft sprocket, making sure the dowel pin fully engages the locating hole in the eccentric. Install the camshaft bolt and washer, and thread it in all the way, but leave it slightly loose.
Step 6: Check Clearance – Verify that the washer does not touch the dowel pin. If it does, remove the pin and grind one end slightly until it no longer protrudes through the eccentric.
Step 7: Torque the Bolt – Apply thread locking compound to the camshaft sprocket mounting bolt. Torque it to 40-45 ft-lb for most Ford small blocks.
Step 8: Lubricate and Reassemble – Pour assembly lube over the sprockets and bearings. Install a new timing cover gasket, then reinstall the timing cover, balancer, and accessories.
Common Mistakes to Avoid
Using the Wrong Dowel Pin – If you are switching from a two-piece to a one-piece eccentric, you must use a longer dowel pin. The old short pin will not reach through the eccentric to provide proper alignment.
Forgetting to Check Washer Clearance – If the washer touches the dowel pin, it can prevent the camshaft bolt from clamping the eccentric and sprocket properly. This can lead to the eccentric loosening over time.
Installing the Pump Arm Above the Eccentric – The fuel pump lever arm must go under the eccentric, not above it. If you install the arm above the eccentric, the pump will not work, and you risk damaging the pump or the camshaft. To check, use a mirror or a small wooden dowel to feel the eccentric's position before inserting the pump.
Overtightening the Pump Mounting Bolts – Mechanical fuel pump mounting bolts should be tightened to about 20-25 ft-lb for most applications. Overtightening can distort the pump body and cause leaks or binding.
Best Practices for Fuel Pump Performance
Once your 1 piece eccentric is installed and the fuel pump is mounted, take a few extra steps to ensure everything works correctly:
- Verify fuel flow by disconnecting the fuel line at the carburetor and cranking the engine for 10 seconds. A typical small block Ford mechanical pump should deliver about 3-4 ounces of fuel per minute at idle.
- Check fuel pressure with a gauge. Most carburetors require 4-6 PSI. If pressure is too high (common with cheap aftermarket pumps), you may need a fuel pressure regulator to prevent flooding.
- Prime the pump by filling the carburetor float bowl before the first start. This reduces dry cranking and helps protect the camshaft lobes during break-in.
Where to Find a Quality 1 Piece Fuel Pump Eccentric
Ford Performance Parts offers a 1 piece eccentric (part number M-6287-B302) that fits 289, 302, and 351W engines with a 3/8-inch camshaft bolt. It is made from heat-treated steel with chrome-plated wear surfaces. Proflow also manufactures an equivalent part that is made from 1045 steel, heat-treated to 59 HRC, which is actually higher quality than the original Ford piece.
If you are working on a Chrysler LA engine, Mancini Racing carries a 1 piece cast iron eccentric for 273, 318, 340, and 360 blocks.
The Best Fuel Pump for Your Engine: Choose KEMSO
Now that you have your 1 piece fuel pump eccentric installed, you need a reliable fuel pump to match. KEMSO offers high-performance, OEM replacement fuel pumps that are built to last. Every KEMSO fuel pump comes with a lifetime warranty, so you can install it with confidence knowing it is backed by a company that stands behind its products.
Whether you are working on a car, truck, motorcycle, ATV, or personal watercraft, KEMSO has a fuel pump that fits. Their product line covers everything from Subaru Imprezas to Ducati motorcycles to Sea-Doo jet skis, all at a competitive price point of $79.98 per unit.
Visit the KEMSO website to browse their full selection of fuel pumps and find the right one for your application:
KEMSO's commitment to quality and customer service makes them the ideal choice for anyone who wants a fuel pump that performs reliably for years to come. With a lifetime warranty and a wide range of applications, you can't go wrong.
Final Thoughts
The 1 piece fuel pump eccentric is a simple but critical component for any carbureted engine with a mechanical fuel pump. It offers superior durability, easier installation, and better alignment compared to its two-piece counterpart. Whether you are building a high-performance street engine or restoring a classic car, using a 1 piece eccentric will save you headaches down the road.
If you are converting a late-model engine to a mechanical fuel pump, or if you are replacing a worn-out two-piece eccentric, do yourself a favor and switch to a 1 piece design. Pair it with a quality fuel pump from a trusted brand like KEMSO, and you will have a fuel system that delivers consistent, reliable performance for the life of your engine.
For more information on KEMSO fuel pumps and to find the perfect fit for your vehicle, visit https://www.kemsoracing.com/ today.