Walnut Blasting Inlet Cleaning

On all of Audi’s FSI engines, fuel is injected directly into the cylinders to improve performance. As a result, the wash effect upstream of the valve or valve stems is lost. This causes a build-up of oily deposits on the inlet valves or seat rings and directly in the inlet channel. The inlet ducts are fed with freshly drawn in air which is also mixed with some blow-by gases from the engine which can contain fine oil particles. The oil residue sits on the back of the inlet valve. Over time and temperature the oily residue is baked into carbon deposits.

The carbon deposits can affect the swirl as the air passes through the manifold, past the open inlet valve and into the cylinder. It can also affect tumble within the cylinder as the piston reaches top dead centre (the highest point the cylinder reaches during the combustion stroke). Deposits cause extra turbulence of the air/fuel mixture inside the cylinder being evenly distributed. When ignited, the flame front can be erratic, leaving unburned fuel and create hot spots in the combustion chamber. Depending on engine type/access removal of the cylinder may be necessary. The procedure involves dismantling valve gear, cleaning all inlet ducts and valves using a chemical compound to dissolve the carbon. Cleaning is then carried out via brushes/compressed air, before reassembling the valve gear and reinstall the cylinder head/s.

Cleaning with chemical substances involves pouring a solution into the closed valves to dissolve the carbon. The chemical cleaner may corrode the valve stem oil seals. Cleaning with chemical substances while the engine is running and in neutral can cause damage to the lambda probes and catalytic converter.

Our new cleaning procedure involves blasting walnut shell granulate with an air compressor (6-8 bar), the fine nut shell granulate is blasted into the inlet duct and onto the valves. The piston must be at top dead centre with inlet valves closed. The contaminated walnut granulate is extracted during the blasting process with an adaptor and an industrial vacuum cleaner.

The walnut granulate removes the carbonisation with virtually no residue. The granulate is soft enough to not cause any scoring/pitting to the inlet duct or valves. Any small amount of granulate residue that does find its way into the cylinder will be burned up during combustion. This is completely fine and will cause no damage to the engine. No damage is caused to the valve stem oil seals, lambda probes or catalytic converter due to chemical substances. Walnut blasting is an affordable and timely repair method, that is also environmentally friendly.