On occasion we see Cummins PT style injectors coming from or being returned by a customer with split injector cups.  In some cases, the damage to the cups can often be difficult to see.  The question then comes up:  "How did this happen"? 

If a Cummins cup splits, there are 2 ways this can happen.

• Water in the fuel:  Water in the fuel can cause a cup to split, although a more common result is that the tip section of the cup is broken off.  What happens is that a drop of water is superheated in the fuel sac, causing extreme stress in this area.  As a result, either the fuel sac portion of the cup breaks off, or in some cases the cup splits.  We have seen cases where a large portion of the cup actually breaks off and causes further damage to the engine.  If this is why the injector cup is split and/or damaged there is usually evidence of water in other parts of the fuel system as well.
• Incorrect overhead settings:  This is by far a more common reason for split injector cups.  This normally happens right after new/rebuilt injectors have been installed, or right after the overhead settings on the engine have been reset.

The solution to the water in fuel issue is easy.  Clean the water out of the fuel system, replace the damaged injectors and carry on!

The solution to the incorrect overhead settings is not always that easy.  First you need to understand that this is not usually the fault of the injector, especially if the injector is a "non top stop" style.

A Top Stop injector has the injector travel set within the injector, and this is done by the injector rebuilder.  Top Stop injectors are normally set in the engine using a "zero lash" setting on the "base circle" of the camshaft injector lobe.  This has become know as the "Inner Base Circle" or IBC method.  The Top Stop setting would have to be set considerably short in order to crack an injector cup.  It is however, a simple matter to measure the injector travel to see if this is why the injector cup cracked.  A Top Stop injector with an incorrect Top Stop setting is not a common scenario.

A Non Top Stop injector has the injector travel set when the injectors are installed into the engine.  There are several methods of doing this:

• The first and most common is by using the "torque" method at maximum cam lift.  This involves torqueing  the injector screw to a given value with the injector plunger at its maximum travel, and bottomed in the cup.  This is known as the "Outer Base Circle" or OBC method.  The torque is is the easiest method of setting an injector, but also the most prone to error!  Suppose that the injector was NOT at its maximum travel, due to problems with the accessory drive pulley (this is where the marks are located), or due to installer error.  Since the maximum lift portion of the cam is a very small portion of engine rotation, proper setting of the engine position is very important.  An in-correct torque value can also cause damage to injectors, especially if this value is too high.
• The other method is to actually set the injector travel from the "Inner Base Circle" or IBC of the camshaft injector lobe using the "dial indicator" method.  This is the preferred method for setting these injectors, and this method is also less prone to error, not to mention that it is a more accurate method of setting an injector.  When using this method, it is very important to insure that the correct travel value is being used.

Our experience has shown that installation issues are  almost always the cause of split injector cups.  As a double check, it is always a good idea to bar the engine over several turns (do not use the starter for this) and then double check your settings.  If the engine is very difficult to bar over on the injector down stroke, it could be that the injectors are set too tight, and this will usually result in damaged injectors.