Ultrasonic cleaning of cylinder heads for automotive repair

Carbon in the chambers and ports, oil sludge under the cam covers, scale in the water jacket, gasket remains on the deck. How a head is stripped, which bath suits aluminium and which suits cast iron, and where cleaning sits between crack testing and valve-seat work.

Technical guide. Figures are taken from our own spec tables; for your process we confirm the settings with a cleaning trial.

A cylinder head comes into the workshop with three kinds of dirt in three places. The combustion side carries carbon in the chambers, around the valve seats and in the exhaust ports. The top carries oil sludge under the camshafts, in the lifter bores and in the oil drillings. The water jacket carries coolant scale and corrosion product. Each has to be gone before the head can be tested, measured and machined, and each is out of reach of a brush somewhere.

Where cleaning sits in the job

Strip: camshafts, followers, valves, springs, seals, injectors and glow plugs out. Valves go into a numbered rack so each one returns to its guide.
First clean: carbon, sludge and scale off, so cracks and warping are visible.
Crack test and measure: dye penetrant or magnetic particle test, deck flatness, guide and seat wear.
Machine: skim, valve seats, guides.
Final clean: chips and cutting oil out of the ports, drillings and bolt holes.
Assemble.

The first clean removes the soil; the final clean protects the assembled engine. The same tank does both, ideally with a bath change in between.

The bath

Head	Liquid	Temperature	Frequency	Time
Aluminium (almost every car head)	inhibited alkaline carbon remover for light alloys	60 to 65 °C	28 kHz	20 to 40 min, with agitation
Cast iron (many diesel and older heads)	heavy-duty alkaline carbon remover	65 to 75 °C	28 kHz	30 to 45 min, soak 15 min first
Final clean after machining, either metal	mild alkaline cleaner with inhibitor	55 to 60 °C	28 or 40 kHz	10 to 15 min

Watch the time on aluminium. A light-alloy cleaner still removes metal if the head is left in it for an hour, and the first thing to suffer is the machined deck. Two cycles with a look in between are safer than one long one.

Cylinder head under cleaning liquid with loosened deposits lifting off — Chambers down, so loosened carbon falls away from the head

Loading

Combustion side down or on edge, so loosened carbon falls away and air escapes from the ports.
Water jacket openings sideways or down, so the scale that comes loose can drain.
Valves, springs and small parts in a separate insert basket, in their order.
On a lift with agitation: the stroke pumps liquid through the ports and the water jacket, which a static basket does not.

Gasket remains

Composite gasket residue softens in a hot alkaline bath and comes off the deck with a plastic scraper afterwards. Multi-layer steel gaskets leave little. Never scrape an aluminium deck with steel, and never use abrasive discs on it: they remove metal and leave grit behind.

After the bath

Rinse in warm water, blow through every oil drilling and water passage, dry in hot air or blow dry, and protect: aluminium is fine left dry, cast iron needs oil or an inhibitor within the hour. Then crack test, while the surfaces are clean and dry; dye penetrant needs a surface free of oil to show anything.

Tank sizes

A four-cylinder car head is roughly 450 × 250 × 150 mm and 10 to 20 kg; an inline six about 650 × 250 × 150 mm; a V8 head half that length; a truck head one-piece up to a metre and 100 kg or more. With the usual 20 mm around the part, a four-cylinder head fits the 580 × 380 × 200 mm basket of the ST-96, a V head fits the ST-157, and an inline six needs the 730 mm basket of the ST-206.

Work	Machine	Useful basket space	Load
Garage, four-cylinder heads	ST-96	580 × 380 × 200 mm	100 kg
Engine rebuilder, inline six and V heads	ST-157 for V heads; ST-206 or an AL-300 with lift for inline six	680 × 480 × 260 mm to 820 × 520 × 340 mm	100 to 200 kg
Truck heads, batches of heads	AL-600 or AL-1000 with agitation and filtration	1170 × 710 × 470 mm, 1420 × 720 × 570 mm	300 kg, 750 kg