By J Narasimhan
INTRODUCTION.
1. Overhauling of engine is a unique rebuild process after a designated period based on exploitation. Overhaul is applied mostly on engine for affordability as replacement involves high costs every other decade. The aim is to restore engine capability to that of a new current generation or new engine. By overhauling, the engine is planned to be retained for few more years, and rebuilding offers a cost-effective option to the state.
2. The Overhaul process is different from regular maintenance and repair processes. In the Overhaul process, the engine is completely stripped to its last component. Then a deliberate inspection is carried out on each component to assess its suitability for reuse. During the overhaul of the engine, first the assemblies are rebuilt by replacing the outlived components by either newly manufactured or reclaimed components. Then these assemblies are integrated as engine.
3. During this process, It can be planned for the unification of various variants received during induction and effect the latest up gradation. This will make further engine management as simple with less inventory.
4. The cost of overhaul is aimed at 30-50% of the original engine to rebuild the engine to perform the same intended purpose.
5. The Overhaul of any engine is carried out after a specific period of exploitation in years or kilometres. Whereas Condition-based Overhaul is now recommended to be more cost-effective. In this, the condition of the major assembly is assessed by various monitoring tools before stripping. The assembly can be stripped and overhauled only when it does not meet the specified limits in that assessment. Otherwise, the same assembly can be reused with superficial maintenance.
TECHNOLOGY
6. The overhaul technology is different from the manufacturing technology. Normally the designer will develop two technologies. One, for manufacturing technology for new engine and another for overhaul with the regeneration process. The transfer of technology (ToT) needs to be different according to purpose.
- One specified value with tolerance for any parameter is applicable in manufacturing of that component. Whereas in overhauling the same parameter will have different values viz permissible value and reclaimable or discord value.
- Means the manufacturing of the component is adhering to a specific value with plus or minus tolerance. The component is rejected if it is not within that limit.
- Whereas in the overhaul process, the same component is assessed after stripping to segregate as reusable if it is within the permissible limit and reclaimed (by rebuild or regeneration) if it is within the reclaimable limit (above discard limit and below permissible limit) and discarded beyond this limit. These limits will be specified by the OEM when he transfers technology for overhaul purposes. Factor of safety is kept in mind by the designer while deciding on these limits.
7. The ToT has to be appropriate for the purpose. Following manufacturing technology is not advisable in the overhaul process for mainly the absence of a regeneration process in manufacturing technology. This makes the overhaul process difficult and not cost-effective. The most important part of ToT is training on the REGENERATION process by OEM/Designer. This includes handling of special machinery/test engine supplied by them for the recommended Overhaul process.
8. The overhaul technology documentation shall include
a) Detailed Project Report(DPR) having building layout, special machinery requirement for reclamation and testing with their installation layout, Electrical points etc) for each dept,
b) Manufacturer recommended spares list (MRLS) for overhaul with source marking for each item (as Import, local manufacturing, and trade items).
c) Manufacturing process documents/drawings (in case items can be manufactured locally),
d) Regeneration process (if the component can be reclaimed) and
e) Testing procedures with Specifications for overhauled engine.
OVERHAUL PROCESS
9. Planning: Planning and control (monitoring) are required in case of overhauling in place of marketing of OE Manufacturing. This function will monitor the target of engine required to be overhauled in a particular year by calling in engine for overhaul through all processes till the rebuilt engine is dispatched with user interactions.
10. Procurement: The spares required will be procured/purchased from authorised sources as per the laid down requirements in the overhaul scale (OHS).
11. Production : This function will perform two process
a) Manufacturing the required spares and regenerate/reclaim the components and bring to their original intended dimensions for reuse.
b) Strip the engine to the last component, clean the stripped parts, and assess the reusability of parts with the help of inspectors. Then rebuild the assembly with serviceable parts (either new or regenerated) and integrate the assembly to as engine.
c) The overhaul process is explained as flow process chart. Apex ‘A’
12. Quality: To carry out a quality audit in receipt (new spares), in process of rebuilt assembly are tested in special purpose test stands , and final testing of the integrated engine in Engine Test House (ETH). Ensuring the quality of the overhaul process is a responsibility of both function viz production and quality as a cross-functional team concept in modern times. This will save time and cost involved in rework. Final quality of overhauled engine is ensured by a designated third party agency before handing over. The details are as given below’
| S.No. | Sub ASSY/ Parts | Parameter |
| 1 | Water Pump | Leakage test at Specified RPM |
| 2 | Oil Pump | No Leakage & Oil Delivery @ specified Pressure |
| 3 | FIP | Calibration & Phasing (firing order setting) |
| 4 | Injector | Pressure Test |
| 5 | Pump Element | Plunger movement timing |
| 6 | Crank Shaft | Balancing |
| 7. | Priming Motor | Pressure testng |
| 8 | Air Compressor | Air Pr bulliding time, oil throw limit |
| 9. | Spring | Stiffness test |
| 10 | Engine | Pr, Power and Torque |
13. Stores: This function will carry the preservation process of parts procured from authorised sources and reclaimed parts atreceipt andmarshaling.
14. Maintenance: This function is to upkeep the serviceability and accuracy of machinery and engine testing house used in the overhauling process.
POST OVERHAUL ACTION
15. The user feedback is obtained after a specific period of exploitation of overhauled engine to analyse and make improvements in the form of correction and corrective action.
Note: This paper is written with the intention to give brief generic information on OVERHAUL PROCESS for its uniqueness to beginners. This concept can be applied to any engine.
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Jagadish Metri
Nice information provided about overhauling of eng in short.