Setting the overhead on a L10

When an engine has all it's components in good working order

It makes any necessary repairs easy.

A Cummins L10 came in for injector replacement.

Injector replacements are, generally speaking, an easy repair. You remove all parts in the way of pulling and replacing the injector and re-install all good working parts as they were.

Not on a L10. When you are reinstalling parts the push tubes don't stay put on the rocker arms like other engines and have to be constantly reset to complete the injector install.
Once the injectors are all installed, after much sweat and swearing, it's time to run the overhead.
This is one of those steps that are made easier by the engine components being in good order to begin with. The overhead is set by matching timing marks up on an accessory pulley and the engine front cover.

This engine's accessory pulley is broken, so the timing marks must be found using a dial indicator.

This is a tool that is useful for mechanical engines, like the L10. The plunger of the dial indicator was set to rest on an injector rocker arm. The engine is then turned over by hand with a breaker bar.

The mechanic watches the dial indicator to see when the hand stops moving, or before the hand starts to travel in the opposite direction. When the hand stops moving is when the rocker arm is at Top Dead Center (TDC). Every time TDC is found, the mechanic makes not of it by checking which rocker arm is at the correct position and marking the pulley with a 1,2 & 3  OR A,B & C for a 6 cylinder engine.