In Situ Crankshaft Grinding Machine for Onboard Repairs

Previously, if a crankshaft in a marine diesel engine was damaged, the entire crankshaft had to be removed and sent to a workshop for repair. This involved dismantling the engine, relocating the crankshaft, waiting for the workshop to be free, and then reassembling and aligning it before the vessel could go back into service. The entire process could take a couple of weeks.


Modern in-situ crankshaft grinding machines have now made it possible to carry out many crankshaft repairs without removing the crankshaft from the engine. The machine is mounted directly on the engine to allow the machining of damaged crankpins and journals at the site.


RA Power Solutions has extensive experience in onboard crankshaft repairs, where removing the crankshaft is difficult or impractical. In-situ machining is chosen mainly for the following reasons: limited space in the engine room, vessel operating schedules, and the need to reduce downtime. However, for successful repair, not only is the grinding machine itself important, but also its correct installation, accurate alignment, and proper operation by experienced technicians.

Why an In-Situ Crankshaft Grinding Machine is Different

An in-situ crankshaft grinding machine has been developed to perform precision machining directly on the engine, compared with a conventional workshop grinding machine. The machine is mounted around the damaged crankpin or main journal, allowing the repair to be performed without removing the crankshaft from the engine.

The primary aims of in situ grinding are:


Rebuild worn or damaged crank pins and main journals.

Bring journal dimensions back to required OEM tolerances

Achieve the desired surface finish (Ra)

Maintain the correct radius on the fillet

Remove the taper and ovality from the quality of the bearing.

Make sure the bearing has good and even contact


The big advantage is that you don’t have to pull the crankshaft and take it to a shop. The grinding equipment is compact and portable, but the repair requires the same accuracy and machining control as a conventional crankshaft grinding process. A reliable repair requires proper machine installation, alignment, measurements, and experienced operation.


Why we use crankshaft grinding machine onboard


On many ships and marine engines it is not always practical to remove the crankshaft for repair. Limited space in the engine room, vessel schedules, dismantling requirements, and the cost of extended downtime can make workshop repair problematic. In-situ machining is a practical and cost-effective solution if the crankshaft is within the manufacturer’s allowable limits for regrinding.


Onboard crankshaft grinding machines allow us to do the following:


Crankpins and main journals grinding on board

Correction of taper and ovality in worn journals

Resurface to the desired Ra finish

Keep the specified filet radius

Journals of machines for undersized bearing shells

Don’t take the crankshaft out and move it around unnecessarily

Reduce engine repair time and vessel’s downtime


The main advantage of onboard grinding is that the crankshaft can be repaired in situ, and the vessel can be returned to service more quickly while still achieving the required machining tolerances. 


Common Crankshaft Defects Repaired

1. Journal Scoring

Scoring generally results from contaminated lubricating oil or inadequate lubrication. Light and moderate damage can usually be removed through controlled grinding.

2. Bearing Seizure Damage

Bearing failure often leaves heat marks, metal transfer, and deep scoring on the journal. Careful inspection determines whether the journal can be reground within OEM limits.

3. Taper and Ovality

Excessive taper or ovality affects hydrodynamic lubrication and bearing life. Precision grinding restores the journal to the specified geometry.

Crankshaft Grinding Machine Installation


Proper installation of the crankshaft grinding machine guarantees accurate and reliable results. The machine is carefully set up, aligned, and checked before machining begins and the grinding can begin.

Before starting the repair the following points are checked:

  • Correct alignment of the machine to the crankshaft journal

  • Run out of journal and use existing

  • Condition and suitability of grinding wheels

  • Accuracy of machine feeding mechanism

  • Arrangement for good lubrication and cooling

  • Adequate clearance of parts of machine and engine

  • Mount the machine securely before starting to grind.


Any slight misalignment can affect the final dimensions, taper, ovality, and surface finish of the journal. This is why careful installation and inspection are critical steps in any in-situ crankshaft grinding repair. 

Grinding Within OEM Tolerances

Maintaining Journal Geometry


Throughout the grinding process, journal dimensions are checked repeatedly to ensure compliance with OEM specifications.


The repair focuses on maintaining the following:


Journal diameter

Roundness

Taper

Ovality

Ra surface finish

Fillet radius


Crankshaft Grinding Surface Finish


The presence of a crankshaft journal alone does not attest to a quality repair. The journal is then ground to the specified Ra surface finish required by the engine manufacturer. The right surface finish is crucial to keep a stable oil film and hydrodynamic lubrication between journal and bearing while the engine is running.


Selection of the Correct Undersize Bearing Shell


The finished diameter of the crankpin or main journal is precisely measured after grinding. These measurements can then be used to determine the correct undersized bearing shell. Before putting the engine back together, check the bearing clearances. This ensures proper lubrication and reliable engine performance.


In-Situ Grinding or Drydock Repair?


In-situ grinding can often eliminate the need to remove the crankshaft from the engine, saving time and dismantling work. But it is not suitable for all situations. If the journal is already at or above the maximum regrind size permitted by the manufacturer, or if there are significant cracks or structural damage, the crankshaft may need to be removed and repaired at a workshop.


Classification Society and Maintenance Records


Crankshaft repairs shall be properly recorded as per the maintenance requirements of the vessel owner. Where applicable, the repair may also need to be inspected or witnessed by the relevant classification society such as DNV, ABS, Lloyd’s Register, Bureau Veritas, ClassNK, or IRS.


Common repair documents are

Initial crankshaft inspection report

Measurements before and after grinding

Crankpin and journal grinding logs

Results of surface finish measurements

NDT reports as necessary

Final inspection report and dimension


Complete repair records provide a clear history of work done and verify that the crankshaft has been returned to the prescribed dimensional and machining standards. 

Uses of a Crankshaft Grinding Machine


The portable crankshaft grinding machine can be used for precision repair in several kinds of engines where the removal of the crankshaft is difficult or unnecessary.


Marine Engine


Main and auxiliary marine engines can be repaired onboard, including the repair of crankpins and main journals. In-situ grinding cuts down on dismantling work and vessel downtime.


Engines Power Plant


A stationary diesel engine used for power generation can be in-situ crankshaft ground. Damaged or worn crankpins and main journals can be machined with the crankshaft in place.


Engine Industrial


Portable crankshaft grinding also helps heavy-duty engines used in industrial and process plants. The machine can be used on crankpins and main bearing journals when the damage is within the allowable limits for repair.


The final decision to grind in situ a journal is dependent on its condition, measurements, manufacturer specifications, and the amount of material that can be safely removed.


Practical Lessons on Board Crankshaft Repairs


Field experience over the years has proven that successful crankshaft repair is not just a matter of removing as much damaged material as possible. The goal is to remove only the minimum material necessary to restore the journal to its original geometry and dimensions.


The condition of a crankshaft can also give useful information about the cause of damage. Heat marks may indicate lubrication problems. Scoring may be a result of contaminated oil or foreign particles. Uneven wear on the journal is indicative of bearing misalignment, overloading, or other engine problems.


These causes need to be investigated before the engine is returned to service. Grinding the journal alone may bring the dimensions back, but if the original cause of damage is not corrected, the same problem can arise again.


By properly installing the crankshaft grinding machine, making accurate measurements, controlling the machining and observing the OEM specifications, many crankshaft repairs can be made without removing the crankshaft. The success of an in-situ repair is not only dependent on the fact that the work is being performed on board but also on whether the same engineering accuracy and quality standards are achieved as if the work were being carried out in a workshop.


Crankshaft Grinding Machine Applications Experience


RA Power Solutions has done the in-situ crankshaft repair of engines of manufacturers such as MAN B&W, Wärtsilä, Sulzer, MAK, Caterpillar, Daihatsu, Yanmar, Deutz, Pielstick, Himsen, Allen, Ruston, ABC, Bergen, Niigata, Cummins, and many other marine, auxiliary, generator, and industrial engines. We have done the in-situ crankshaft repair with our Crankshaft Grinding Machine (CGM).


We have performed in-situ crankshaft grinding and repair in over 100 countries, providing shipowners, offshore operators, power plants, engine manufacturers, and industrial facilities with onsite machining solutions.


In addition to on-site crankshaft grinding, we provide inspection, repair, rebabbitting, and manufacturing services for main bearings, crankpin bearings, connecting rod bearings, thrust bearings, white metal (Babbitt) bearings, and engine bearing bushes. These capabilities allow for multiple engine repair needs to be met with a single engineering service, helping to reduce downtime and maintain the required OEM specifications.


“We also have available engine crankpin bearings in our stock.” For more information, visit now: https://rebabbittingbearing.com/ 


Contact our engineering team for more information about crankshaft grinding machines, in-situ crankshaft grinding, onsite crankshaft repair, crankshaft polishing, and related engine repair services.

For more details of the repair of the engine, please email us at rajshahani@rapowersolutions.com or info@rapowersolutions.com or call us at +91 9582647131 or +91 9810012383.

Source URL: https://www.crankshaftgrindingmachine.com/crankshaft-grinding-machine/
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