Q:

I have a 1961 Corvette problem, and I hope you can help me.


Last week, my fuel pump failed. I bought a new one from a Corvette parts vendor in my area. I installed it with no difficulty, but when I tried to start the engine, I heard an odd noise, and it wouldn’t start. I took the new pump back off of the engine only to find that the push rod was severely bent. I don’t know how this happened, but I must have done something wrong when I installed the new pump. How can I get the new pump installed properly, without the danger of damage to the engine or the pump?


A:

I have seen this problem before, so I think I can help. When you installed the new pump, you probably got the actuating lever misaligned.


The fuel pump push rod is driven off of a special lobe on the engine cam shaft. As the engine turns, the cam shaft turns that lobe and drives the fuel pump. The push rod, climbing the lobe of the cam, will push the actuating lever on the fuel pump, which in turn compresses the spring inside the pump. As the cam turns further, the lobe turns around to the heel portion. The push rod continues to follow due to the spring in the pump. The fuel pump spring, because it has been energized by mechanical energy through the cam, will apply fuel pressure for the engine’s fuel system in relation to the tension of the spring. A stiffer spring will provide more fuel pressure, and a lesser spring will provide less fuel pressure. This is the means by which the fuel pressure is adjusted.


Because the. lobe turns with the cam shaft, when you stop the engine, the lobe may end up in any position. That is, the cam lobe may be on the heel of the cam, the portion where the push rod is all the way retracted; or it may end up on the toe. If it ends up on the toe, or near the toe, the push rod will be in the position where it is compressing the spring of the fuel pump.


Now, we finally get to the part where we address the problem you may have had when you installed your new fuel pump.


If the cam shaft was on the toe, or near the toe of the cam; it made it difficult for you to install the new pump. As you try to install the pump into the cavity on the side of the engine, you must push the pump into position against the pressure of the spring inside the fuel pump. The fact that the cam is on or near the toe makes it difficult to hold the pump in position, against spring tension, while installing the bolts and tightening them. It is during this process that the pump is accidentally allowed to wiggle around, and the lever of the fuel pump may slip off of the end of the push rod. Since the pump is still loose on the mounting, it is difficult to see that it is off center. As you tighten the bolts, the pump is forced to a straight position which can bend the lever or the push rod. The lever and push rod are inside the cavity where you cannot see. You will probably not know that the push rod is off of the lever until you start the engine.


The push rod may be bent when the fuel pump bolts are tightened, or, when the engine is started. When the cam shaft turns, the push rod forces the lever sideways, and damages the push rod, the new pump or both.


How do we avoid this problem?


There is a simple way to avoid the stress of trying to overcome the pressure of the fuel pump spring while installing the attachment bolts.

You simply turn the engine around, while holding the push rod up against the cam shaft until you get to the heel portion of the cam lobe. (That is the portion where the push rod is all the way into the engine) If you can get a friend to help, you could hold your finger against the end of the push rod, forcing it against the cam lobe as the engine is manually turned. Always turn the engine in its normal direction, that is, turn the crank shaft counter clockwise as viewed from the driver’s seat.


If you plan to turn the engine with the starter motor, you must use extreme caution. You must ground the ignition system so the engine cannot start. Then, you must remove the drive belt so that no accessories will turn. After these things have been done, it is possible to carefully turn the engine; in short clicks, with the starter motor, and manually follow the movement of the cam shaft to the heel portion. This is the position where the push rod is all the way up into the engine cavity.


The next problem that has to be solved is the problem that the push rod will fall down, by gravity so you cannot get the fuel pump lever under the end of the push rod. Each time you try to install the new pump; the push rod will drop down, right in the way of the pump lever.

This is easy to solve. The small block Chevrolet V8 has a provision to help with the installation of a fuel pump. There is a threaded hole in the front of the engine, right in alignment with the cavity of the push rod. It is located on the front face, at the same level as the fuel pump, between the pump mount and the timing cover. You will usually find a bolt in this opening on the front of the engine, which is acting as a simple plug to fill the hole during normal operation. This hole is threaded, as I have mentioned, for a standard 3/8” X 16 USS size bolt. It will have a 9/16” wrench size. Remove that bolt. Find a longer bolt with the same size diameter and thread gauge. It should be about 2” long. Thread that bolt into the opening, and it will bump against the push rod inside the engine. By hand, not with a wrench, tighten that bolt just tight enough to hold the push rod up, out of the way, so you can install your new fuel pump without interference from the push rod trying to drop down.


Once that has been done, the fuel pump can be installed more easily. The new pump will be easy to hold in place because the tension of the spring is minimal due to the cam shaft being on the heel of the lobe. Also, it will be easy to place the pump in position because the push rod is held up, out of the way by the 3/8” bolt.


After installation, be sure to remove the long bolt that you used to hold the push rod, and re-install the shorter bolt that was originally installed in the opening. Don’t forget to remove the ground wire from the ignition system and re-connect the drive belts.


It may seem like a complicated task, but, in fact, these simple steps will save time and make the process successful.