Big Rig Basics
June 2009 28 TrucKers News T he cylinder head on your diesel helps contain the high-pressure gases inside the cylinder and al-lows the intake and exhaust valves to open at the right points in the engine's rotating cycle. The valves allow the exhaust to blow out of the head after the power stroke of the piston and let in fresh air on the intake stroke. Properly maintained, the valves will last the life of the engine. But poor maintenance or extreme oper-ating conditions may cause them to fail because of excessive pounding or overheating. The valves ride inside guides, which are narrow tubes that hold them in position so they move straight up and down. The valve guides in a heavy-duty diesel can be driven out of the cylinder head and replaced. Valves have a circular bottom with a cone-shaped male face that sits against a similarly shaped female surface in the cylinder head. The seating surfaces are part of replace-able valve seats located in the bot-tom of the cylinder head. Rebuilding a head involves forc-ing out the valve guides and seats, replacing them, then seating the valves in a grinding process that helps them seal effectively. The job also involves dozens of precision checks, such as making sure the head is still perfectly flat on the bottom (machining it flat often is necessary). To avoid errors, most engine dealers send a cylinder head with failed valves or other parts back to a remanufacturing center for rebuilding on a production line. This is cheaper than on-site hand labor and gives the user an excel-lent warranty that can be used ev-erywhere. So, for most truck users, getting this work done involves having an engine dealer remove the cylinder head from the engine, send it to the factory and replace it with a remanufactured head that is on hand. REMOVING A HEAD A Drain the cooling system, then remove parts like the intake manifold, turbocharger and any other parts like the air cleaner and intake tubing that will get in the way. Unbolt the cam cover and pull it off. B Disengage the mounting bolts for the engine brake and re-move it. C Remove the rocker mounting bolts and the rocker levers that operate the valves and injectors. The technician, Ruben Quesada, removes Valve Job Any cylinder head work requires expert precision for guaranteed reliability big rig basics John BaxTer A B C photos: john baxter