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OM 636 HISTORY
Its design was derived from the M 136 petrol engine fitted to the earlier 170V and with which it shares many dimensional similarities and internal components.
Numerous automotive applications of the OM 636 include the Mercedes-Benz Unimog 2010, 401, 402 and 411 models and the 319 series transporter as well as in forklift trucks, farm tractors, combine harvesters and other special purpose vehicles. The OM 636 was also used to power electrical generators and stationary water pumps.
Readily marinised by fitment of a heat exchanger and sea-water cooling system, the OM 636 is popular in many yachts and cruisers throughout the world. Over the years, it has earned an enviable reputation for excellent fuel economy and durability which contributes to its continuing popularity with boat owners in the 21st century.
During the 1960s, 70s and 80s, the OM 636 was marinised by a number of specialist firms throughout Europe. Among them Wizeman WM-36 (Germany), Volvo Penta MD4 (Sweden), Renault RC40D (France), Solé Diesel SM-636 (Spain) and Nannidiesel 4.180 (Italy/France).
In the UK, the 42 HP OM 636 was marinised and fitted with a Bowman heat exchanger and a belt-driven Jabsco sea-water pump as shown in the picture above.
After the end of production in Germany, the engine continued to be manufactured under licence in Spain - a testimony to the successful original design. Perhaps the most recent application of the OM 636 was in Thermo King refrigeration units fitted to trucks transporting perishable goods.
OM 636 TECHNICAL DESCRIPTION
The cast iron crankcase has integral cylinders with a standard bore of 75mm. Re-boring is possible up to a maximum bore of 77mm. Pistons are available in 4 repair sizes. It is also possible to reline the block back to standard bore.
The injection pump and oil filter are located on the right hand side of the engine (as seen from the flywheel end). The generator, starter motor, oil dipstick and breather pipe are on the left. At the front, an alloy timing cover encloses helical gears driving the camshaft and injection pump off the crankshaft. A side cover seals the valve lifter chamber. The alloy oil sump is bolted to the crankcase.
The cast iron cylinder head is fastened to the crankcase by hexagon-head bolts. A composite cylinder head gasket seals the combustion chambers and water passages between the head and the crankcase. The cylinder head features removable precombustion chambers into which injectors atomize the diesel fuel for combustion. Pre-heater plugs are used as a starting aid. An alloy rocker cover with an oil filler seals the top of the cylinder head.
The 3-main bearing, drop-forged crankshaft has hardened bearing surfaces. The centre bearing serves as the thrust bearing. Counterweights on the crankshaft compensate for the rotational inertia in relieving the forces on the main bearings. The coolant pump is driven by a 'V' belt pulley fitted to the front of the crankshaft.
The forged steel connecting rods are equipped with bronze bushes at the small end to accommodate the piston pin and a 2- piece friction bearing at the big end. The bearing cap is secured to the connecting rod by 2 special bolts and nuts.
The alloy pistons generally feature 3 compression rings and 2 oil scraper rings. The floating piston pin is retained by circlips. The piston crown is dished.
The drop-forged camshaft with hardened bearing surfaces and cams is supported by 3 alloy bearings in the crankcase. Axial movement is controlled by the front camshaft bearing which together with the 2nd camshaft bearing is of a split design.
Each cylinder features an overhead exhaust and inlet valve opened and closed by the camshaft by means of mechanical lifters, pushrods and rocker arms.
The fuel lift pump is mounted on the injection pump and draws fuel from the tank. It incorporates a hand primer pump that is used the bleed the fuel lines of air (e.g. after filter replacement). Diesel fuel is fed to the injection pump after passing through a filter. The low pressure of this fuel feed to the injection pump is regulated by a pressure relief valve fitted on the fuel filter head. The injection pump delivers fuel under high pressure to the injectors via rigid injector pipes of equal length. On engines fitted with BOSCH injectors excess fuel is returned to the fuel tank by a metallic spill pipe interconnecting the injectors. A flexible fuel spill hose is used on engines fitted with TDZ injectors.
Depending on application, the injection pump is fitted with a pneumatic or centrifugal governor that controls the amount of fuel injected according to engine load. On engines producing the maximum 42HP an automatic timing device advances the timing of the pump with increasing engine speed.
Engine lubrication is provided by an oil pump driven by the camshaft. Oil is drawn from the sump and directed into the main oil gallery after being filtered by a fine mesh strainer or cartridge-type filter. Oil is fed to the crankshaft and camshaft bearings via small bores. From the front camshaft bearing, oil continues to the rocker shaft pedestals and cylinder head through external oil lines. The rocker arm bearings and pushrods are lubricated by oil flowing through hollow rocker shafts. Cylinder bores, piston pins and timing gears are splash-lubricated. Two pressure relief valves are fitted to the oil circuit. The main circuit features a relief valve that opens at 8 bar, protecting the engine against excessive oil pressure. The oil filter is equipped with a valve that opens at 2 bar allowing oil to by-pass the filter should it be clogged. Most installations feature an electrical or mechanical gauge to monitor the engine's oil pressure.
The injection pump and cooling water pumps have their own oil supply and are not connected to the main engine lube circuit. However, modern replacement water pumps feature sealed-for-life bearings and require no maintenance.
Engine temperature is controlled by means of a belt-driven coolant pump, a radiator or heat exchanger and a thermostat.
RECONDITIONING AN OM 636 ENGINE
Engines to be reconditioned should be completely disassembled and chemically cleaned, the engine block and cylinder head pressure-tested and oil galleries cleaned. Any damaged studs on the block or head should be renewed.
Engine blocks that were not originally fitted with liners should be bored out and honed to the next repair size up to a maximum bore of 77mm. Blocks fitted with liners can be bored to the 1st repair size 75.50mm or the liners replaced.
Cylinders must be bored and honed to accommodate new pistons. Crankshafts checked, reground and polished. All crankshaft and camshaft bearings should be systemically replaced. The camshaft and timing gears checked and replaced if necessary. A new oil pump should be fitted before mounting the sump to the crankcase.
Cylinder heads must be refaced within given limits and the valve seats reworked to ensure the correct valve height. Ensure that the latest valve guides are fitted. These have an external annular groove to fit a valve stem seal. Early engines do not have a valve stem seal but feature a valve spring retainer with an extended sleeve. Inlet and exhaust valves should be replaced if necessary.
When disassembling the cylinder head, the precombustion chambers should be removed and bead blasted for thorough inspection. Removing these pre-chambers can be a tricky procedure without special tools but it is strongly recommended since they are invariably coked up.
Attention should be paid to the condition and wear of all valve train components especially on high mileage engines e.g. valve lifters, pushrods, rocker arms, adjustment screws and rocker shafts. Rocker shafts usually show signs of wear and scoring and should be replaced. The lubrication of the rocker shafts is assured by the external oil lines and these should be carefully checked or replaced if in poor condition.
Whilst the core engine is being rebuilt, it is advised to have the diesel fuel injection pump and the injectors checked and recalibrated by a competent diesel engineer.
New gaskets and seals should be used throughout the rebuild.
If facilities are available, rebuilt engines should be run on a dynamometer for several hours to confirm power output, oil pressure and exhaust emissions.
The engine can now be completed with its external ancillaries according to its specification and application. Marine engines will require the fitment of a heat exchanger, sea water pump, starter motor, alternator, hoses and pipe work. All these components will need to be checked, reconditioned or replaced.
In order to protect the engine from external corrosion, especially important in a marine environment, completed engines should be degreased, etch-primed and painted prior to installation.
This will then result in a ready-to-fit marine engine.
OM 636 NEW SPARE PARTS AND REBUILD KITS
Our stocks include:
ENGINE CRANKCASE, FRONT COVER AND OIL SUMP
Full engine gasket
CRANKSHAFT AND PISTONS
bearings: standard and all undersizes
DIESEL FUEL INJECTION EQUIPMENT
diesel fuel injection pumps
Fuel filter elements
We also offer a replacement fuel filter assembly featuring a screw-on disposable filter which can be replaced without detaching the filter head from its mounting. It can be specified for remote fitment to a vertical or horizontal mounting surface.
Inlet manifold for
glow plugs to be wired in parallel
The original oil filter assembly on the engine can be replaced with a modern replaceable spin-on filter fitted at a convenient location in the engine compartment. Enquire for further details.
Fresh water pumps with
Vacuum pipes from
injection pump governor to throttle body
OM 636 engines marinised by Nanni were fitted with either a Nanni or a BOWMAN heat exchanger. Although external parts specific to the Nannidiesel heat exchanger fitment are no longer available, it is possible to re-marinise the engine by fitting a new Bowman heat exchanger together with the associated pipe work. Please contact us for more information.
A copy of the original operating and service instruction booklets is available together with a parts illustration catalogue showing exploded view diagrams of the engine components.
To receive a compilation of technical and parts bulletins for this engine, please send a message indicating your email address.
So whether you need a gasket or an engine rebuild kit - contact us to discuss your requirements.
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Click below to see
an OM 636 engine sitting on a testbed