Housing

What is an Air Compressor Housing?

An Air Compressor Housing is the main structure of the compressor that produces pressurized air in the air brake system of trucks, buses and trailers. It carries the cylinder block, crankcase and bearing bores, and holds the compression and lubrication sections together. Its job is to keep the moving parts aligned and guide oil through its internal passages. The part that wears most is the inner cylinder surface and the bearing bores; as the cylinder scores, air leaks and compressor output drops. In the workshop and parts trade it is also known as the compressor body, compressor block or compressor casing.

How does an Air Compressor Housing work and what parts does it include?

The housing holds the compressor's moving parts together and contains the oil passages that carry lubricant to the bearings and piston area. It includes the following sections:

• Cylinder block: the space inside which the piston moves and air is compressed.
• Cylinder liner: in some designs, a separate sleeve forms the inner surface of the cylinder.
• Crankcase: the lower section that houses the crankshaft mechanism and holds the lubricating oil.
• Main bearing bores: the seats for the crankshaft and bushings.
• Oil galleries: internal channels carrying oil from the crankcase to the bearing and piston area.
• Head mating face: the flat surface where the valve group and head seat with a gasket.

Air Compressor Housing types

• Single-cylinder housing: carries a single cylinder block, so it is used in compact compressor types.
• Twin-cylinder housing: has two cylinder bores and a common crankcase, chosen according to the required air capacity.
• Air-cooled housing: has cooling fins on its outside and is cooled by airflow.
• Water-cooled housing: has internal coolant passages and connects to the engine cooling circuit.

How to choose the right Air Compressor Housing?

To find the right housing, check the casting code, head connection layout and number of cylinders of the removed compressor together. Looking at the outer appearance alone is misleading, since housings that look alike can have different bolt holes and oil passages. Even within the same model series, Mercedes-Benz, MAN, Scania, Volvo and DAF use different layouts, so choosing by model name alone is a mistake. Referring to the removed part along with its mating surfaces is the safest method. Even when the mating surfaces are sound, the condition of the internal channels should be checked separately.

Fitting and maintenance points

• Oil passages: clean the channels before fitting; a blocked passage leaves the bearings without oil.
• Cylinder surface: if scored, honing (correcting the inner cylinder surface) may be needed; a rough surface damages seals and the piston.
• Mating faces: head and crankcase faces must be flat, and old gasket residue must be scraped off before a new gasket is fitted.
• Crack check: inspect the housing visually before fitting and confirm with a leak test if needed.
• Bolt holes: a hole with damaged threads must be repaired before the head is fitted, since loose bolts increase air leakage.

Common faults and fixes

• Air leak under the head: the head mating face may be warped or the gasket seat damaged; resurface the face and fit a new gasket.
• Leak noise and pressure drop from the cylinder: the cylinder bore may be scored; repair the surface or renew the liner.
• Oil increase or oil leak in the crankcase: an oil passage may be blocked or the crankcase gasket may have failed; clear the passages and renew the gasket.
• Housing overheating: cooling fins may be dirty or water passages blocked; clean them.
• Crack in the housing: can result from freezing, overheating or impact; a cracked housing should be replaced with a new one.

Frequently Asked Questions

Can a cracked housing be repaired?

Small cracks may be assessed by a specialist workshop. A crack in the cylinder block or bearing bore is not acceptable from a safety standpoint, and the housing must be replaced. The location of the crack is important in deciding whether the housing is still usable. A repaired housing should not be returned to service without passing a leak test.

Does the valve kit also need replacing when the housing is replaced?

If the head connection matches, the old valve kit can be used, but its valves should still be checked for wear. If the head mating face and gasket seat do not match the new housing, the valve kit must also be replaced.

How can a blocked oil passage in the housing be recognised?

Heating at the bearing area, a falling oil level in the crankcase or abnormal noise can indicate a blocked passage. The channel should be cleaned through the housing and its flow checked. Even if the channel looks open, the internal flow should be checked separately. Do not proceed to fitting until the blockage is cleared.

What is the difference between buying a housing and a complete compressor?

A housing covers only the main structure; the piston, crank and valve group must be sourced separately. A complete compressor includes all the necessary internal parts. Without comparing the removed part first, it is hard to tell which option is needed.

Why is the casting code on the housing important?

The casting code is the most reliable sign of which compressor type the housing belongs to. Outer appearance can be similar, yet the mating faces and oil passages may differ. If the code cannot be read, judge the removed part from a photo together with its mating faces.