Signs of Unit-Injection related damadge on the cylinder head

  • Bad starting behavior of your engine (especially when warm or after a longer period without use)
  • unsteady engine-rpm in idle
  • dying in city traffic
  • power loss
  • loss of compression
  • diluted engine oil due to leaked diesel at cylinder head
  • missing / low oil pressure (bearing shells already worn out by diesel in the oil)


What is damadged?

The design-related, one-sided attachment of the Unit-Injectors (UI) in the cylinder head, creates a significantly increased load on the seats on the opposite side of the attachment shoes. The sealing surface is damaged over time, resulting in the leakage of diesel into the cylinder head, as well as a lack of fuel injection pressure. The hitherto usual way to repair required the replacement of the cylinder head. A recurring damage was nevertheless inevitable, since the basic principle remained unchanged. The Unit-Injection-Rail provides a permanent solution to this problem without having to replace the damaged cylinder head. Nevertheless, it is recommended to install it as a precautionary measure in order to minimize damage to the cylinder head in advance.


The figure shows a section through the cylinder head in the area of the unit-injector. You can also see the one-sided mounting shoe, which fixes the UI in its seat.

By tightening the mounting screws, the mounting shoe would start to tilt. This is structurally prevented by a bearing / support surface to the cylinder head on the mounting shoe (arrows white). However, this results in a high lateral force with which the UI is pressed obliquely into its seat (arrows red). The opposite area of the sealing surface is heavily loaded (area yellow).

This enlarged section shows the area of the sealing surfaces in undamaged condition.

Over time, the Unit-Injector travels further to the right due to the slanted tension force, until finally the body of the UI begins to touch / damage the seat area (areas red - metal on metal).

Finally, if this area (red) has been damaged to a certain extent, and thus the UI has traveled a corresponding distance in this direction, then the sealing rings can no longer close the resulting gap on the opposite side. The result is leaking diesel in the cylinder head with the familiar symptoms.


USE of the Unit-Incection-Rail

The basis for using the UI-Rail is the fact that during the process described above, the seats in the area of the seals themselves are not damaged (areas green). Here metal does not hit metal, but only the rubber of the sealing rings touches the aluminum of the cylinder head. The result is damage to the seal (flattening), but no damage to the seats in this area. A centered Unit-Injector, without the above-mentioned lateral forces, also seals in this damaged seat.

The U-bars (yellow) of the UI-Rail support the adjacent Unit-Injector on its body and thus prevent tilting, as well as the described lateral force of the one-sided attachment. Via the connection bar (green), the UI-Rail forms a common, rigid structure, which fixes the Unit-Injectors exactly vertically and centered in the seats. Tipping / moving is excluded - a permanent tightness is guaranteed.

Through the UI-Rail, all Unit-Injectors are connected and are being pressed into their seats evenly. They are thus kept from tipping and remain permanently tight in the seats. A damadge of the cylinder head is prevented.

Installation is carried out without changes / work on the engine / cylinder head. Original screws and fixing points are used!

The easy-to-understand step-by-step installation instructions (see tab "Downloads") allow the repair to be mastered even by untrained Do-It-Yourself workers.