Mercedes-Benz OM 352 straight-six diesel engine

Daimler Benz
Mercedes-Benz OM 352
Production period:	since 1963
Manufacturer:	Daimler Benz
How it works:	diesel
Engine Type:	Six-cylinder in-line engine
displacement:	5675 cm 3
Fuel supply:	direct injection
Power:	48-127 kW
Successor:	OM 366

The Mercedes-Benz OM 352 is a straight-six diesel engine (OM = oil engine) with direct injection from Daimler-Benz AG , which was produced in 1963 in the Mercedes-Benz Mannheim plant and from 1970 by various licensees in series. This was introduced in 1964 at the Geneva Motor Show . From 1966 the engine was also available as OM 352 A with turbocharger . Later there were also multi-fuel variants and based on the OM 352 models with intercooler . For NATO also has foreign detonator(M 352). Due to the large model range of the OM 352 series, some engines are also referred to as the OM 353 and OM 344 . To use the engine came mainly in medium-duty commercial vehicles of the brand Mercedes-Benz , but was also used in machinery and vehicles of other brands. This is considered very reliable and has great power reserves. The OM 352 belongs to a small OM-300 model family , more than 300,000 copies made.

The development of the OM 352 began in the early 1950s . The pre-chamber engines of the OM 302 series were developed in the 1940s, but were not used due to the war. Only the successor series OM 312 was produced in series. To further enhance performance, the engines were drilled and equipped with new prechambers, but the new OM 322 series engines did not prove to be stable because the prechambers reached the limit of thermal capacity. The development of an engine with direct injectionwas at Daimler-Benz in 1956 the highest priority. After various attempts, the engine was finally built with a central injection nozzle and a cylindrical combustion chamber in the piston. As the engine was ready for production, there was initially bottlenecks in engine production, so that in 1963 only a small number engines produced, which was primarily in truck production in Wörth. Only from the summer of 1964, the engine was available in sufficient quantities. The 1966 offered supercharged engines have loaders from Eberspächer , Garrett or Kuhnle, Kopp & Kausch . 

Technology 

The OM 352 is a straight - six inline four - stroke diesel engine with direct injection , pressure circulation lubrication , OHV valve control and water cooling . Its displacement is 5675 cc. In a cylinder bore of 97 mm and a piston stroke of 128 mm, the engine is as long Huber designed that its rated power at 2800 min ^-1 achieved. The activities range from 48 kW as the naturally aspirated engine ( Unimog 406 ) up to 127 kW as a supercharger engine; the engines designated OM 362 LA with additional intercooler achieve an output of 141 kW. 

The crankcase of the OM 352 is made of a gray cast iron alloy and consists of two parts, the lower part of the crankcase with the oil sump and the upper part with the cylinder bank and the camshaft . The cylinders have no liners. upper and lower parts of the crankcase are connected at the height of the horizontal center of the crankshaft. On the power output side, the housing for the clutch is flanged at the location of the flywheel . Various components such as oil filter housing, alternator and starter are bolted to the outside of the crankcase. 

The pistons were supplied by Mahle and are forged from light metal . They have three compression rings and two oil scraper rings, and transfer the power to the crankshaft via inclined connecting rods made of tempered steel . The material of the connecting rod bearing shells is lead bronze , they are enclosed in a steel support shell. The crankshaft is also made of tempered steel and forged, it is stored seven times, the bearings are made like the connecting rods made of lead bronze. The crank webs are provided with counterweights, behind the crankshaft, which drives the camshaft, a vibration damper is mounted. 

The OM 352 has one cylinder head for all six cylinders, made from a molybdenum - chromium cast iron alloy. The cylinder head gasket is made of asbestos .In essence, the cylinder head is divided into two parts, the valve drive side and the intake pipe that is not flanged to the cylinder head, but are integrated into this. The intake pipe is designed as part of the cylinder head.  This design already existed at the Daimler-Benz prechamber. A total of six paired swirl channels lead from the intake manifold to the intake valves, next to which the exhaust valves are located. The inner two pairs of cylinders each share an outlet channel, while the outer cylinder each have their own outlet channel (see picture on the right), they open below the intake manifold in the exhaust manifold  , which is a Vierfachkrümmer. If you look at the engine from the front, the rocker arms and injectors are located to the left of the intake manifold. The four-hole injector within the cylinder head and are inclined to the combustion chamber at an angle of 30 °. The usual in an OHV engine bumpersfor the valve train, the OM 352 is guided through the cylinder head opposite the exhaust side. Around the cylinders, between the exhaust ports and around the lower part of the injectors and valves, the cooling jacket is drawn.

Externally, the cylinder heads of OM 352 and OM 352 A differ in the position of the air intake and the design of the exhaust manifold. In the naturally aspirated engines, the air filter box is mounted centrally on the cylinder head, while the four-flow exhaust manifold leads down. When Unimog 406 additional cyclone filter could be provided for the suction motor on request. The supercharged engines have a forward or rear air intake, to which the exhaust gas turbocharger is directly attached, because the engine has no intercooler. The exhaust manifold is also four-flow, but led upwards, so that the exhaust gas flow can drive the turbine wheel of the turbocharger. From the turbocharger, the exhaust gas is directed down through a flanged manifold to the exhaust. The exhaust gas turbocharger is connected to the lubrication system with a separate oil pressure line. The hot oil flows from the loader back to the oil cooler via a second pressure line. Between the exhaust manifold and cylinder head cover runs a manifold for the cooling water of the engine, which opens on the front of the engine and is connected there to the tube cooler. At the end of the exhaust manifold immediately in front of the turbocharger, a throttle is installed, which is used as an engine brake. About this device, the engine is turned off.

The camshaft in the crankcase is mounted four times and made of hardened tempered steel. It is flange-shaped at its front to receive the helical drive wheel. Between the flange and the drive wheel another gear is mounted, which drives the injectionpump. In the middle of the camshaft is a drive wheel for the oil pump of the engine. The valves hanging in the cylinder head, each cylinder an inlet and an exhaust valve of the same size are actuated by bumpers and rocker arms of the camshaft  , valve seat rings, the engine has not.The rocker arms are mounted in pairs on a total of six Kipphebelböcken and are pressed on the rocker shaft with springs against the blocks.  The fuel is delivered by a Bosch inline injection pump to the four-hole injectors,  which is driven via the mentioned gear from the camshaft. The engine has a felt tube fuel filter.

The oil pump is placed in the middle of the engine in the oil sump. It has a short suction tube with suction funnel and strainer to suck the oil out of the oil sump and then feed it through the main flow filter to the main oil line. In addition, there is a bypass filter; behind the oil pump outside the oil pan hangs the main oil filter. At the top of the cylinder head hangs an oil separator, which is connected to the crankcase with a fixed pipe. Furthermore, the engine has an oil cooler , which is flanged to the crankcase below the exhaust manifold. He is lapped by the cooling water of the engine. The hydraulic centrifugal pump is built into the cylinder head on the face of the engine, it will, as well as the alternator, driven by a V-belt.  The fan is mounted on the shaft of the water pump. The engine has a cooling water thermostat and a remote thermometer. Depending on the purpose of the engine it is designed for 12-volt or 24-volt electrical system. The 12-volt electrical system has a 12-volt alternator with a power of 0.24 kW and a 12-volt thrust -armature starter with a power of 3 kW  installed; same 12-volt push-rod starter is installed on the 24-volt on-board power supply, but a more powerful 1.5-kW 24-volt alternator starts charging right from the start of the crankshaft revolution. Some models still have a 24 Volt starter with a power of 4 kW. As another Nebenagreggat the motor has a pneumatic compressor .