601 602 603 Injection Pump Delivery Valve Seal Replacement

Common fuel leak problem but repair must be approached with care

On the 4, 5 and 6 cylinder aluminum head diesel engines produced from the mid 1980's to the early mid 1990's one of the more common fuel leaks comes from age hardened delivery valve seals on the top of the injection pump. The delivery valves are enclosed in round housings that are mounted between the top of the pump and the metal hard line fittings going to the injectors. If you notice any wetness around that top part of the injection pump it is a good indication that the o-ring seals have failed.

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Problem & Solution

Common among these chassis:


Replacement is not difficult for the D.I.Y. mechanic, provided he has good instructions, the correct seals, the special socket needed to remove the housings AND a mind for cleanliness and careful attention to detail. Our special repair kit (as shown to the right) comes with all these except the socket. The socket can be ordered separately. Only you can provide the needed care and cleanliness.

Most repairs are straight forward and uneventful but we have had reports of problems after the o-rings have been replaced. The first indication of a problem will come when you start the engine and hear a loud knocking or nailing noise from one or more of your injectors. Air in the fuel lines can cause this but if it does not go away after the engine warms up it usually means one of three things (2 directly related to the delivery valves and one related directly to the fuel injector nozzle). 

1. Even the smallest spec of dirt entering the delivery valve or holder can cause the valve to not seat properly against the copper washer or the valve itself to "hang up" leading to incorrect fuel delivery to the injector (this is what can cause the knock). Remember it will only take a spec of dirt and Kent thinks this is one of the biggest reason for post-repair injector nailing.

2. If any of the delivery valves are not installed properly, this can also lead to incorrect fuel delivery. This could mean one or more may have been installed without the spring, or the valve upside down, or the valve bound up during tightening. 

3. If any spec of dirt works its way up to the fuel injector that can cause the nozzle tip inside the injector housing to "hang up" and this will also cause loud injector nailing. 

Now you can understand why this job must be done with such care. The engine area around the injection pump needs to be super clean before you begin. Compressed air is a must. Keep both your tools and hands super clean during the job.

WARNING: When trouble shows up Kent suspects the following:

Right behind the problem with particle contamination, he believes some people get in trouble by pulling too much out of the pump, getting confused and then not putting everything back in correctly. The spring can fall out when the holder is lifted off the pump. Only the valve needs to come out in order to get to the crush washer, and it MUST go back in exactly with the same end up as when you removed it! Remove only the parts that are necessary to replace the oring and crush washer. Do not remove the outer barrel of the delivery valve or it may not re-seat properly.


Take pictures of how things come out or draw pictures. Pay particular attention to how the valve is installed. On most engines you will find a machined band around the valve for reference. Do not mix parts. Place parts on super clean surface and clean and blow dry before re-oiling and installing.

If you are working with the injection pump on the engine resist the temptation to remove all of the delivery valve holders at one time. Instead, plan to replace only one crush washer and o-ring at a time. Once you install them, screw the delivery valve holder down by hand (if you lube the O-ring you should have no issues screwing it in by hand). Before you torque the holder sight down or lay a straight edge across the tops of the delivery valves to see if the one you worked on is sticking up higher than the others. If it is, you know you have a problem inside and will have to remove it and find the problem. 

Our kit comes with complete instructions. These warnings and recommendations are shared here to help make you aware of potential problems if you choose to take this job on yourself.