A Yanmar engine turbo increases the volumetric efficiency of the engine by as much as 300 per cent. Turbos use the pressure and velocity of the exhaust stream to turn the turbine mounted to a common shaft with the blower. The blower draws outside air and compresses it, which increases the density of the intake air and boosts the engine's power. Poorly tuned engines and long periods at low RPMs cause carbon deposits, or coking, to build on the turbine and turbine housing. High levels of coking can choke the turbine and lead to an unbalanced condition of the turbo.
Inspect the individual turbo components before you clean them. Check for carbon build-up around the turbine shaft seal, turbine blades, heat shield and inside the bearing chamber. Look for signs of poor lubrication such as wear, burning and discolouration of the turbine shaft journal, thrust bushings and washers, floating bushings and the inner bearing race of the bearing chamber. Look for signs of oil leakage inside the turbine chamber, around the heat shield, the turbine seal ring and the turbine blade, inside the blower and on the back of the blower seal plate.
Boil the carbon deposits off of the turbine and the turbine chamber parts. Place a 5-gallon metal bucket on a burner and bring about 3 gallons of water to a boil. Place the parts in the water and boil them until the carbon loosens. Carefully clean the parts with a plastic brush. Soak the parts with a carbon cleaning agent and brush it until the parts are free of carbon. Clean all of the other turbo parts with fresh diesel fluid. Be careful to not scratch any of the surfaces of the turbo parts. Do not beat on the parts to remove the carbon. This will damage them.
Things You Will Need
A clean, metal 5-gallon bucket and a heat source is needed to boil the carbon off of the turbo parts. Use only clean, fresh water. Use a quality carbon removing agent to remove the stubborn carbon deposits that do not boil off. Scrub the parts with a hard bristle or plastic brush to avoid scratching any of the closely machined surfaces of the parts.