TIE ROD/STAY BOLT

Tie rod are made of milled steel. 

Functioning of Tie Rods

Tie rod is a long strong rod with bolts or tie bolts at both the end. This rod holds the three major engine components i.e. Cylinder block or entablature, “A” frame, and crankcase in compression and transmits the firing load to the bedplate.

The tie rods are fitted through the above mentioned components and are hydraulically tightened so that the whole engine can be held in compression.

Tie rods are placed as close to the centreline of the crankshaft of the engine to minimise the bending moment on the transverse girder.
In Sulzer, for fixing brg cap, Jack bolts are used, which are hydraulically stretched and tightened, so that tie rods can be brought to the center. The oil from the main sys goes into the stay tube till half the collar for cushioning effect, and is drained when the engine is stopped.
In MAN B&W, brg cap flange studs are brought closer to centerline so that tie rods are placed closer to the centerline.

Effect of loose or broken tie rod

If the tie rod bolts are loosen or broken, then the marine engine will show the following abnormalities:

• It will lead to vibration of the marine engine.

• It will lead to fretting of mating surface of the engine.

• It can lead to crank shaft misalignment.

• Such prolong condition may lead to bearing damage.

• Foundation bolts and chocks may get loose.

• Turbocharger of the engine will be affected as it’s a high speed machine. A little vibration in the machine can damage or misalign the rotor or damage the bearing.

What are the Causes of Tie-Rod Breaking?

• The material and threading of tie rod are under rated and not properly machined.
• Aging of tie rod leading to failure or breakage.
• Tie rods are not properly tightened.
• Tie rods bolts are over tightened by hydraulic pressure crossing its elasticity limit.

• Engine is over loaded or peak pressures of the cylinders are very high.
• Previous fretting of engine mating surface.
• Foundation bolts have become loose or chocks are damaged leading to transmission of vibration in to tie rods.
• Tie rods consist of Jacking bolts/pinching bolts, if they are loose it will lead to heavy vibration leading to loose or crack in the rod.
• Scavenge fire loosen the rods as they pass from the scavenge space and the heat leads to the expansion of the rods.
• If the ship face very heavy weather, the fluctuation in the marine engine load may cause loosening or breakage of the rods.

PROCEDURE TO REMOVE BROKEN TIE ROD

1.    CUTTING method which is not recommended as it leaves many wear particles in the system and is not easy to completely clean the system.

2.    HYDRAULIC JACK

3.    ELECTROMAGNET

4.    WINDOW METHOD in which a window is cut in the A-frame. A clamp is made  and using a wire sling, pulled up. This method requires CLASS for approval after welding.

5.    Breaded wire dia 7mm