Rebuilding A Pontiac fuel pump
When rebuilding the original is the best way to go
Jim Black - August 01, 2011 09:00 AM
For Your Information:
Jim Mott Restorations
Paragon Corvette Reproductions
1 Schematic view of fuel pump.
2 Here’s our original pump, GM part number 5621733. After removal from the engine we thoroughly washed the exterior of the pump with cleaning solvent to remove all traces of dirt and grease. We lightly scratched locator marks on the fuel cover and pump body for proper alignment of the inlet and outlet openings during our reassembly.
3 Holding the pump in place on a bench, we carefully removed the four screws retaining the pulsator cover, removed the cover and pulsator diaphragm. You could also do this by clamping the rocker arm in a vise with the pulsator cover facing upward. A vise with brass teeth jaws is easier on parts.
4 We carefully removed the fuel cover screws and separated the fuel cover from the pump body by jarring it loose with a light plastic hammer. Then we twisted the fuel cover with diaphragm still attached, by hand, breaking the slotted rod link and pulled it from the pump body freeing the diaphragm and spring.
5 Here, we carefully separated the old diaphragm from the fuel cover revealing the inlet and outlet valves.
6 Then, using a 3/8-inch drive extension, we carefully drove out the old valves alternately from each side, taking care not to damage the valve seats.
7 Next, we clamped the pump body in a vise and drilled into the rocker arm pin slightly, then drove out the rocker arm pin with a tapered drift. The pin easily collapses as it moves through the pump body. You might need to remove sufficient staked material from the pin first, but take care, as you’ll need to reuse the rocker arm pin later during reassembly.
8 With the rocker arm pin driven out, we removed the rocker arm, rocker arm spring, and link. Take note of the positioning and style of the rocker arm and levers.
9 Final disassembly included removal of the oil seal with a hook-shaped tool or screwdriver. We used care not to damage the seal seat in the process.
10 After complete disassembly, we cleaned all metal parts in solvent and blew out all passages with an air hose and inspected all reusable parts for damage.
11 We used a rebuild kit purchased from Paragon Corvette Restorations. The 16-piece kit included most wear items with exception of a new rocker arm pin which must be reused. In addition, some rocker arm levers may or may not be included with the kit, requiring reuse.
12 Here, we have our new kit parts along with our reused original parts laid out and ready for reassembly. We had our pump body re-plated in yellow dichromate by Daytona Parts Company, and also bead-blasted the original cast aluminum fuel cover and pulsator cover.
13 We started the reassembly by installing a new seal in the pump body recess with rubber end down. We set the seal retainer in place using an adequately sized socket and tapped it into place, then staked the die-cast lip in four places to help retain it.
14 After soaking the new diaphragm in clean kerosene (or fuel oil) we placed the diaphragm spring and diaphragm into the pump body and clamped it into a vise with cloth-protected jaws. The cloth helps protect our new finish from scratches. Be sure and rotate the diaphragm link 90 degrees to the rocker arm to ease installation in the following step.
15 A close up of the pump flange reveals the date-code (6550DE). Deciphered, the number 6550 is the GM short number for the part, D (April), and E (year, 1965).
16 We inserted the rocker arm assembly into the pump body and hooked the diaphragm pull rod link, then installed the rocker arm pin into place.
17 We rotated the pump in the vise, placed a new washer, and then staked the pin to hold it in place.
18 Next, we turned our attention to the fuel cover and installed the new inlet and outlet valves (which are identical) using an 11/16-inch socket with 3/8-inch drive and a small hammer.
19 The outlet valve must face the bottom of the cover with the inlet valve facing upward. We secured each valve by staking. Here’s a view of the fuel cover with the new valves installed properly.
20 We joined the finished fuel cover to the pump body with new bolts supplied from our kit, taking care to line up the scratch marks for proper alignment of the inlet/outlet openings.
21 Here, we installed the new pulsator diaphragm and joined the pulsator cover to the fuel cover with new bolts supplied. We also installed the new rocker arm spring compressing it into position.
22 We installed new fuel line fittings and our rebuilt fuel pump is now ready for installation.
A multitude of decisions are required in the restoration of any classic or muscle car. In most cases, the decision to rebuild individual parts rather than replace them is often the best in the interest of correctness and/or originality, which follows the real definition of a true “restoration”.
This is especially true when the car being restored has nearly all its original parts still intact. Case in point was the recent restoration of a ’65 GTO by Jim Mott Restorations, of Kimberly, Idaho. Many individual components were rebuilt and restored to their original appearance, including the original fuel pump, among others. With Jim’s help we’ve decided to give readers a better understanding of the fuel pump itself and to provide guidance to those “do-it-yourselfers” who might tackle a rebuild on their own.
The function of any fuel pump is to transfer fuel from the tank to the carburetor(s) in sufficient quantity to handle engine requirements at any speed or load. The rocker arm spring keeps the rocker arm in constant engagement with the eccentric on the engine’s camshaft, so that the rocker arm moves up and down with each camshaft rotation. As the rocker arm is moved down, it bears against a link which is pivoted on the rocker arm pin.
This link is hooked to the diaphragm pull rod so the diaphragm is moved away from the fuel chamber and the diaphragm spring is compressed. The enlarging fuel chamber moves gasoline from the tank through the fuel line and inlet valve into the space below the diaphragm. As the rotating eccentric permits the rocker arm to move away from contact with the link, the compressed diaphragm spring is free to move the diaphragm downward to push the fuel through the outlet valve to the carburetor bowl.
Because the diaphragm is moved downward only by the diaphragm spring, the pump delivers fuel to the carburetor only when the pressure in the outlet line is less than the pressure maintained by the diaphragm spring. Fuel is delivered to the carburetor only when the carburetor’s needle-valve is open. When the needle-valve is closed by the pressure of the fuel on the carburetor float, the pump builds up the pressure in the space below the diaphragm and in the outlet tube until the diaphragm spring is compressed. The diaphragm then remains stationary until more fuel is required. Our pump generally maintains fuel pressure at about 5¼ to 6¾ pounds.
Our stock GM fuel pump, part number 5621733 (AC Delco #6550), is a mechanical-diaphragm type with a three-piece component. This basic pump style can be found on many GM V-8 models from 1956-’66, and we’ll use a kit from Paragon Corvette Reproductions for the rebuild. The sequence of rebuild will include complete disassembly, cleaning and inspection, sending out parts for plating, bead-blasting parts and final assembly. The following photos and captions detail the procedure, so follow along.