Effect of operating an engine with loose tie bolts:

.lose tie rod .ltr .ltb

Cylinder beam would flex and lift at location of slacken tie bolt.
Rigidity of whole structure will be destroyed
Noise & vibration will increase
Other tie bolt will be overloaded leading to fatigue failure
Machined mating surfaces will rub together and wear away … fretting
Due to Fretting, Machined faces would eventually be destroyed.
If fretting and tie bolts are tightened, cylinder to piston stroke alignment destroyed.
If tie bolts are tightened on damaged face, bending moment is induced in tie bolts
Misalignment between bedplate, frame and entablature
Misalignment between xhead guide liner and stuffing box leading to excessive wear.
Misalignment of main bearing and other sliding surface
Transverse girders bend which could lead to cracking

The tie bolts are located close to the centre line of the engine

The combustion forces acting on the cylinder head passes through the tie bolts
As load increases tie bolt tend to pull transverse girders upward and load on bearing pockets tend to push downward. So the transverse girders are always subjected to a bending moment which is restricted by tie bolts
As bending moment is the product of force & distance, the greater the distance, the greater would be the bending moment
So, to avoid excessive bending moment tie bolts are located as close to the centerline of the engine as possible.