Crankshaft Breakdown

Wow! Not so loud!

Near the end of you shout, you tell us "MAIN BEARINGS 5,6 & CON.ROD BEARINGS IN BETWEEN THESE MAIN BEARING WERE SEIZED." Let me see... engine and load running, bearings seized, load still turning, (rotation torque applied to immovable shaft)... twist on crankshaft... Seems like the next event is foreseeable.

Seems the question should be "... WHY THESE BEARING WERE SEIZED?" Was there sufficient lube oil? How about the cooling system?

they are not normaly solid there are drillings fro the oil, these holes and the sharp edges near the webs are areas for fracture. main bearings seizing puts load on crank next time firing takes place and large load is applied crank splits neat sharp edges and drillings its fairly common for fractures near the web.

if your going to rebuild change the oil pump as well

It will help if you send some pictures from the broken parts and from the failed bearings.

Without a picture the comments are hypothetical, with a picture they can be better.

It will also help if you can give some dimensions in order to allow a better analysis.

3.47 MW CAT-3616 ENGINE WAS RUNNING ON 2200 KW ONLY , ALL TEMPERATURE PRESSURES OF COOLING WATER & OIL WERE NORMAL ABOUT HALF AN HOUR BEFORE THE INCIDENT. ENGINE TRIPPED ON LOW LUB.OIL PRESSURE ( 3.0 BAR) NORMAL PRESSURE FOR THE ENGINE IS 5 .0 BAR. HERE ARE PICS FOR CRACKED WEB , B/E BEARINGS LOWER HALVES.

I shall try an explanation although I still do not enough to be sure of it:

1- The cracks are in the region where the notch effect under bending is the highest. The way the crack developed indicates a high bending stress.

2- Due to the wear of bearings 5 and 6 the crankshaft under the piston force had the possibility to deform more till the load was transmitted to bearings 4 and 7.

3- This increased the "free" bending length by a factor of 3, the rest of the crankshaft was, with respect to bending, maintained in line by the other not worn bearings. The maximal bending moment went up by same factor as lever arm this increased load being too much for the sections.

This is according to what I saw on your pictures and making usage of your description a logical explanation. The shaft failure is due to the lubrication failure and to the bearings radial wear (succession lubrication failure → high temperature → bearing wear → deformation freedom for the shaft under piston load → bigger bending moment → higher stresses → fatigue (olygocycilc) failure.

If I am not clear enough - it is always difficult to explain - let me know and I shall make a sketch.

THANKS A LOT, I GOT YOUR POINT. BUT IT WAS OBSERVED RIGHT AFTER THE INCIDENT THAT SUFFICIENT RATHER MORE THAN ENOUGH OIL WAS FLOWING THROUGH THE DAMAGED BEARINGS AS COMPARED TO OTHERS , OIL ROUTE IS FROM OIL GALLERY TO MAIN BEARING THEN TO ADJACENT CON . ROD BOTTOM END BEARINGS THROUGH WEBS. SO LUBRICATION FAILURE MIGHT BE THE ONE OF SERIES OF CAUSE & EFFECTS BUT I AM AFRAID DOES NOT SEEM ROOT CAUSE FOR THE INITIATION OF SERIES OF FAILURES WHICH ENDED UP TO C/SHAFT BREAKAGE.

ONCE AGAIN THANKYOU VERY MUCH . WAITING FOR YOUR COMMENTS .

B. REGARDS

The crack indicate VERY clear to be the follow up of a overload in bending.

Which ever the reason would be the bearings wear allowed a surplus of bending and generated the crack, if this one is or not due to lack of lubrication that you can better investigate since you are on the spot.

However I think that if the engine worked for a long time without problems and fails out of a sudden by bearings wear it is most probable that the wear is due to lack of lubricant in the sliding zone. How do you explain the bearings wear if enough oil was available ?

May I make a remark using capital letters means that you shout! If you look at all comments we do use capitals ONLY if a word has to be marked as important in the text. So please use our code same way.

If you want more input you should make more pictures and allow a free look at the crack, as it is now the studs are hiding part of it. Can you give some dimensions for the shaft diameter width ? If we have them we can better analyse the bending. Piston D? Stroke ? Power ? RPM ?

First of all , i am really very sorry for using capital letters. Now regarding the c/sh breakdown, I will be back with more clear pictures & all relevant data very soon.

Thanks & regards