To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. When the piston is just after the top dead centre (TDC), the pressure inside the cylinder can rise as high as 140 bar. This acts - PowerPoint PPT Presentation

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PPT – To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. When the piston is just after the top dead centre (TDC), the pressure inside the cylinder can rise as high as 140 bar. This acts PowerPoint presentation | free to download - id: 68f999-ODkwM



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To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. When the piston is just after the top dead centre (TDC), the pressure inside the cylinder can rise as high as 140 bar. This acts

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Tie rods or Tie bolts To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. – PowerPoint PPT presentation

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Date added: 18 August 2020
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Title: To understand the role played by tie rods, it is necessary to appreciate what is happening inside the cylinder of the engine. When the piston is just after the top dead centre (TDC), the pressure inside the cylinder can rise as high as 140 bar. This acts


1
Tie rods or Tie bolts
  • To understand the role played by tie rods, it is
    necessary to appreciate what is happening inside
    the cylinder of the engine. When the piston is
    just after the top dead centre (TDC), the
    pressure inside the cylinder can rise as high as
    140 bar. This acts downwards through piston rod
    and connecting rod, pushing the crankshaft down
    into the bearing pockets. At the same time, the
    pressure acts upwards trying to lift the cylinder
    head.

2
  • The cylinder head studs screwed into the
    entablature prevent this happening and so this
    upward acting force tries to lift the entablature
    from A-frame and the A-frame from the bedplate,
    putting the fitted bolts in tension. As the
    piston moves downwards, the pressure in the
    cylinder falls, and then rises again as the
    piston changes direction and moves upwards on the
    compression stroke. This means that the fitted
    bolts are under cyclic stresses, which they are
    not designed to withstand. This would lead to
    disastrous consequences.

3
  • To hold the bedplate, A-frame and entablature
    firmly together in compression and to transmit
    the firing forces back to the bedplate, long tie
    bolts are fitted through these three components
    and tightened hydraulically. To prevent excessive
    bending moment in the transverse girders, the tie
    bolts are positioned as close as possible to the
    centre of the crankshaft. On some engines to
    achieve this, jack bolts are used to hold the
    crankshaft main bearing cap in position instead
    of the conventional studs and nuts.

4
  • Operating the engine with loose tie bolts will
    cause the fitted bolts, used to hold the bedplate
    , A-frame and entablature together in alignment,
    to stretch and break. The machined mating
    surfaces will rub together, corrode and wear away
    (fretting). Once this has happened, the alignment
    of the engine running gear will be destroyed.
    Loose tie bolts will also cause bending of
    transverse girders of bedplate to bend, which
    could lead to cracking and misalignment of the
    main bearing.

5
  • Once fretting between the mating surfaces has
    occurred, then tightening of the tie bolts will
    pull the engine out of alignment. The crosshead
    guides, the cylinder liner and the stuffing box
    will no longer be in line and excessive wear will
    occur. Because the tie bolts will no longer be
    pulled down squarely, they will be subjected to
    forces which may lead them to breaking. If
    fretting has occurred, then only solution is to
    remove the entablature and/or A-frame and machine
    the fretted mating surfaces (a very costly
    exercise).

6
  • Tie bolts can break in service. To reduce the
    risk of this happening, they must be checked for
    tightness (not over tightened). If a breakage
    does occur, the engine may be operated for a
    limited period on reduced load, without replacing
    the broken tie bolt.

7
  • On MAN-BW MC-C engines, the tie bolts do not
    pass through the transverse girder in the
    traditional way. Instead there are two pairs of
    tie bolts fitted on either side of the single
    plate A-frame and screwed into the transverse
    girder of the bedplate. They claim that this
    reduces the distortion of the bedplate during
    running of the engine.

8
  • When checking of the tightness of the tie bolts,
    refer to the manufacturers instructions for
    tightening pressures of the hydraulic jacks and
    the order in which to carry out the check. The
    normal order is start at the centre and work
    outwards, checking the bolts in pair. The MC-C
    engines with twin bolts is an exception starting
    forward and working towards after side. If the
    main bearing is fitted with jack bolts, then it
    must be slackened before tightening the tie
    bolts. Any pinch bolts fitted must also be
    slackened off.

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