Crankshaft bearing failure
Crankshaft bearing failure is a common issue that can lead to significant damage to an engine. In this blog post, we’ll explore a real-life case study of crankshaft bearing failure to understand the causes, consequences, and remedies.
In this case, we’ll look at a Marine engine that had been serviced regularly and well-maintained. Despite this, the Generator experienced a catastrophic engine failure caused by crankshaft bearing failure. We’ll examine the symptoms that led up to the failure, as well as the root cause of the issue.
By analyzing this case study, we can learn how to identify the warning signs of crankshaft bearing failure and how to prevent it from happening in the future. Whether you’re a mechanic or a car owner, this post will provide valuable insights into how to protect your engine and ensure its longevity.
What Happens when bearing fails?
The shift Engineer had observed Heavy smoke from the Breather line followed by obnoxious noise from the Engine. He immediately stopped the Engine and opened up the Crankcase doors after about 15minutes for inspection to assess crankshaft bearing failure. Upon opening up the doors following damages have been observed.
- Conrod bearing # 6 was found roBearing of connecting rod no. 6 was found damaged due to rotation with the crankpin in the housing.
- The flow of White metal was seen from the Conrod big-end collars.
Unit # 6 was pulled out from the position and further inspection revealed the following.
- Both the bearing shell halves were found rotated in the housing.
- Bearing metal up to the steel backing was found rolled out and thinned up.
- The white metal has got stitched with the crank pin.
- Conrod big end serrations were found damaged.
- Symptoms of Big end bore overheating have been observed.
- Small end bush has also suffered metal flaking in the 1” area.
- Connecting rod bolts were having the symptoms of overheating and suspected to be elongated.
- Cylinder Liner was pulled out and vertical seizure marks have been observed
NDT test report
To investigate the crankshaft bearing failure damaged/affected area on Crankshaft NDT for superficial cracks, internal cracks and Hardness affected part was subjected to NDT test and the following results were recorded.
- DP test- NRD
- MPT- NRD
- Hardness test
Opinion & Adv
Jobs to be carried out
- White metal to be removed from the crankpin and to be polished properly.
- Crankpin is to be subjected to MPT, UST & Hardness test
- Crank deflection is to be checked.
- Neighbourhood unit to be inspected for any damage.
- Crankpin is to be checked for taper and ovality
What causes crankshaft failure?
I was contacted by a client to attend to this Engine that had suffered crankshaft bearing failure from overheating on its MAN/B&WL23/30 H type Engine.
During the inspection we observed a connecting rod big end bore enlarged and the reason was cam wear of crankshaft pin caused overheating of the bearing. Deep scratches were developed and crankpin surfaces were damaged.
This has also caused Distortion of CR big-end bore, cracks in the journal surface as well as damaged fillet radii.
Our technicians performed local grinding to determine the depth of the cracks and hardness testing to determine whether or not the hardness levels were acceptable.
The important task was to find the extent of the damage to the crankpins and to the main journals. We calibrated and tested the following.
Measurement of Maximum and minimum diameters taper and wear of damaged crankpin.
2) Connecting rod bores for dimensions and wear.
3) The run out of adjacent main journal to check for heat induced bents in the crankshaft.
4) Amount of cam wears in each of the crank pins.
5) To carry out the non-destructive testing on all the crankpins including the damaged pin, using magnetic particles and ultrasonic for heat cracks both on the surface and the sub surface of the damaged crankpin.
Measured Hardness readings are produced below.
|Free end fillet Radius||265|
|Deive end filltet||292|
|10 mm Away from Rear side||578|
Recommended Hardness Value= 225 to 265 BHN (crankshaft bearing failure)
Comprehensive testing and profiling of hard spots and bands on the damaged crankpin.
7) Conditions of the existing bearings.
The crank pin was finish machined to a diameter of (- 1.0 mm) well within maker limits.
After our tests, we decided
a) Crankpin # 6 must be ground 1mm undersize to remove hard spots and heat cracks.
b) All main journals must be inspected & polished to remove surface scratches.
c) The bent Crankshaft at main journals # 6 and 7 and had to be straightened.
The investigation findings were useful since we could get the re-usability of significant components like the Crankshaft and the period required for the entire repair.
Knowing this, the service team could and did schedule other maintenance that Hass was carried out at the same time.
With the gathered information we could identify the spares, well ahead of time correctly, that would be required for reassembly and re-commissioning of the engine..
The Crankshaft had suffered a heat-induced bent due to crankshaft bearing failureat the main journals # 6 and #7. The stress relieving was achieved by using a peening hammer on the heat-affected crankpin # 6. After this stage of the repair, the run-out of the Crankshaft was restored to 0.025mm, which was precisely at Builder’s Specifications.
Crankpins #6 was ground to the specification sizes. Work was carried out on 16 hours basis using one grinding turbine to speed up the repairs.
While grinding was in progress, removed the cylinder liners, Servicing of Cylinder heads was performed.
In house quality control system requires that Monitored these grinding repairs daily with the following checks:
1) All micrometers were calibrated using “Standard” bars.
2) Presence and conditions of heat cracks checked by Magnetic Particle Inspection technique
3) Carried out the Hardness testing using handheld portable electronic testers to determine the degree of existing hardness and the sizes of affected areas.
Grounded The fillets adjacent to the bearing landing surfaces achieve a smooth transition to the webs and provide a good oil flow for the cooling lubrication oil.
Finally, the crankpin was polished with an oscillating superfinishing machine to obtain a finish of 6 micro-inches.
Inspected all the main journals, and scratches were polished.
After careful cleaning, the engine was rebuilt using a new bearing with 1mm downsize. Tested the engine and opened the bearing d to determine the contact pattern.
- The crankshaft was straightened to 0.03mm.
- The ovalty and taper of the reground crankpins was a maximum of 0.03mm
- The reground crankpin was held to 0.05mm for the parallelism
- Restored the hardness of the reground crankpin to 250 Hardness Brinell except at one spot o 500 Hardness Brinell.
Removed all heat cracks
CRANKSHAFT ANNEALING AND MACHINING REPAIRS
Machining of new fillet radii
· Magnaflux crack testing and Hardness testing
· Local grinding to determine the crack depth
· Removal of cracks by rough machining before heat treatment
· Removal of crankpin journal hardness by annealing process.
· Finish machining to (– 1.00 mm undersize)
TIMING ( Job Completion)
I, along with my Service Manager, arrived at the site within 2 hours of the accident. We went ahead for the investigation for Crankshaft & Bearing failure analysis
Inspection and complete testing and calibration took one day.
The work for the critical Repairs continued on a 24 hours basis
It took almost three days for the Grinding of #6 crankpin, including fillet regrind and super finishing. Super finishing /Polishing of each main journal & crankpins took us 4 hours each.
SPARE PARTS CONSUMED (crankshaft bearing failure)
|Sr. No.||Part Description||Qty|
|11||Small End Bush||02|
|12||Connecting Rid Bearing (-1.00D)||01|
All the pistons were dismounted and dismantled. After cleaning and checking we have observed that following small end Bushes were damaged.
Cylinder unit no.1 Con Rod, IMO – 0802, 0
Connecting rod of Cylinder no.1
Cylinder unit no.2 Con Rod, IMO – 0802, 00.07.13,
Measurement of connecting rod was carried out and readings recorded are as under.
|Sr. No||110 K||88 K||144 K||11 M (new)||143 K||150 K|
One no. connecting rod replaced in the Cylinder Unit no 6 with new one.
Clearance in the small end & piston pin
|Sr. No||110 K||88 K||144 K||11 M (new)||143 K||150 K|
Damages due to bearing failure
We salvaged the crankshaft bearing failure -crankshaft within maker limits. Without the combined grinding and annealing process, this crankshaft would have been condemned and required costly replacement
Failed Parts images
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