Tie bolts,

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These are positioned at each transverse girder. They are intended to keep the transverse girder in compression at all times thus minimising risk of fatigue cracking. Correct tension is therefore important and this should be checked regularly in accordance with the engine manufacturers instructions, this normally means retensioning the bolts in pairs from the center of the engine. alternately for'd and aft.

Tie-rods are often in two parts for ease of manufacture and fitting when head room is restricted. This also makes changing the bolt in the event of breakage simpler

Pinch bolts are fitted at certain points to prevent vibration which can induce stress and cause fatigue.These must be released before the bolts are retensioned

Tension should be checked at set intervals, following a scavenge fire, after application of an excessive load, following grounding or collision, or where the landing face have become suspect. Tiebolts are susceptible to fretting, often indicated by the presence of red dust (sometimes called cocoa) around the nut. In the event of this it is important to check the condition of the nut landing and to ensure before retightening that the surface is clean and free from moisture.

The most common method for applying the correct tension to the bolt is by use of hydraulic jacks. These are mounted on the tiebolt thread above teh nut. The jack stretches the bolt by acting on a removable sleeve surrounding the nut. Once the bolt has been extended the nut may be rotated via slots cut into the sleeve allowing access. Pressure is applied as per manufacturers requirements which extends the bolt within its elastic limit, the nut is screwed down hand tight and the pressure released. A second method involves the nut turning to handtight, then by use of a gauge the nut is rotated a further angle.

Tie-rods are nor required on medium speed engines generally because the relatively thick sections used means that stress is lower.

Opposed piston engines do not require tie-rods because combustion load is transmitted from the crankshaft to the bedplate is very low.
Modern trends
The traditional through tie bolt is being supersceeded by shorter twin stay bolts which have the advantage of reducing distortion of the main bearing keep