Silentbloc engine

An engine mount is an elastic mounting that connects the engine and, depending on the version, also the gearbox to the chassis or subframe. It absorbs vibrations, torsional shocks and structure-borne noise transmitted to the cab, while preventing uncontrolled movement of the drivetrain. For MAN and Mercedes trucks, buses and vans, engine mounts vary considerably depending on chassis configuration, engine output, gearbox and mount position. Therefore, always identify engine mounts using the chassis number; visual comparison or selection based solely on the model name is never sufficient.

Engine mountings include rubber-metal mounts, conical elastomer mounts, hydraulic engine mounts and combination brackets with integrated stop bushes. The metal inner sleeve must fit the mounting point with the correct press fit or bolt preload, while the outer sleeve distributes the load within the support bracket. Rubber hardness, generally expressed in Shore A, together with the geometry determines the permissible movement and vibration damping. A mount that is too hard causes cab resonance; a mount that is too soft or torn causes engine tilting and excessive load on exhaust flex sections, coolant hoses and propshaft connections.

The correct version depends, among other things, on the engine family and vehicle application. This applies to MAN D08-, D15-, D20-, D26-, D28- and D38 engines, and to Mercedes OM 364-, OM 366-, OM 402-, OM 421-, OM 422-, OM 441-, OM 442-, OM 457-, OM 460-, OM 501-, OM 502-, OM 503-, OM 904-, OM 906-, OM 926-, OM 934-, OM 936-, OM 470-, OM 471- and OM 473 engines. Especially on heavy six-cylinder and V engines, engine weight, reaction torque and the position of the gearbox mount affect the required load rating of the engine mount.

Typical defects include cracked or hardened rubber, failed vulcanisation between the rubber and metal sleeve, reduced mount height and worn mounting holes. Prolonged exposure to engine oil, hydraulic oil, diesel or coolant damages elastomers and reduces their damping performance. On hydraulic mounts, traces of fluid around the housing indicate an internal leak. Common symptoms include a knocking noise when pulling away or changing gear, increased vibrations at idle, resonance within a specific engine speed range, torn exhaust rubber mounts and accelerated wear of the clutch or universal joints.

First, with the engine switched off, inspect all mounts, support brackets, fastening bolts and stop points for cracks, sagging and contact marks. Then measure the clearance between the engine mount and the stop using a vernier caliper and compare the left and right sides; a clear difference in height often indicates a collapsed element. Use a vehicle lift and support the engine in a controlled manner with a transmission jack. Move the drivetrain only minimally up and down: excessive relative movement, metal-to-metal contact or a loose inner sleeve confirms a defect. Then, following safe working procedures, have a second technician briefly apply torque in forward and reverse gear. Observe engine tilting and first rule out faults in the clutch, gearbox mount, propshaft or exhaust system.

Preferably replace damaged engine mounts as a mounting pair when both sides are of the same age and subject to the same load. Support the engine and transmission without stress before removing fasteners; securing a mount while under torsional load significantly reduces its service life. Clean mating surfaces, replace damaged spacer bushes and use the specified new stretch bolts where applicable. Only tighten fasteners to the specified torque when the engine mount is in its normal driving position. After installation, check the alignment of the exhaust, air lines, coolant hoses and driveshaft.

In the event of recurring damage, the cause must be eliminated: leaking engine oil on the rubber, a cracked engine mount bracket, defective transmission mounting or abnormal engine shocks caused by irregular combustion. Technical support and a wide availability of the right components help keep downtime for trucks, buses and vans to a minimum. The Braem team is always ready to help you.