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Engine Maintenance_Connection Rod Bottom End

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[MUSIC] [MARITIME TRAINING SERVICES INC.] [In case of any conflict between the requirements shown in the movie and the company's safety management system (SMS), please follow the company's SMS requirements.] [ENGINE MAINTENANCE: CONNECTING ROD BOTTOM END] [MUSIC] The engine of a ship is the heart of a vessel. When the engine is damaged or suffers from a failure, it not only costs a substantial amount to repair, but it puts you and your fellow seafarers in serious danger. Without a functional engine, vessels are at risk of drifting, grounding, collision and capsizing, among other serious hazards. Investigations into cases of auxiliary-engine damage, highlight that human error is often the main cause, with the majority of all damage taking place immediately after maintenance work. The most highly-stressed part of the engine, are the bottom-end bolts or studs of the connecting rod. These bolts are hydraulically stretched or tensioned, using special jacking equipment. Assessing these components is the most critical element of any engine overhaul. Many auxiliary engines have suffered catastrophic failures, due to incorrect tightening of connecting rod bottom-end nuts. Most of these failures did not occur because engineers' lack of knowledge of how to tighten the nuts, but because they used an incorrect technique. In this video, we will explain how an engineer, following the manufacturer's method, while working on these critical components, can apply a special technique, to effectively and safely keep the nuts tight until the next overhaul. This process occurs within 4 broad steps: 1. Disassembling the bottom end bolts and studs of the connecting rod, making sure to check and record release pressures during disassembling. 2. Inspecting the components for wear-and-tear, by performing visual checks and dye-penetrant tests. 3. Testing for ovality by assembling the bottom end without bearing shells and taking measurements. 4. And, reassembling with the bearing shells for use, being sure to double-check for tightness. [SOUND OF ENGINE WHIRLING] [DISMANTLING THE BOTTOM-END] To start an inspection or overhaul of the bottom end of the connecting rod, you need to disassemble it. But, before you begin work, first, make sure you fully understand the latest manufacturer's service letter or bulletin. Additionally, take a moment to ensure that your pressure gauge is calibrated before you begin. The bolts or studs cannot be unscrewed by hand, until they have been hydraulically extended. This commonly done with jacks that consist of spacer pieces and ring-tight jacks. The connecting rod could have 2 or 4 bolts or studs, and should have matching numbers of jack sets to unscrew them. Two jacks can be used to dismantle 4 bolts, if one jack of the set of 4 is damaged. The method shown here is safe and effective in any of these cases. But, make sure you are always using a manual-hydraulic pump, and never a pneumatically-driven type. Pneumatic pumps can too easily over-tension the bolts. Start to disassemble the bottom end of the connecting rod, by assembling the hydraulic-jack components on each of the bolts or studs. Compress the jacks by screwing the piston down tight, using the tommy bar. Do not do this step using force, wrenches or other forceful tools. Once the jacks are compressed, back them by 1/2 a turn. This is important, as you will not be able to remove the nuts without this step. You'll learn exactly why you need to do this a little later. Raise the hydraulic pressure steadily, until the nuts are able to be unscrewed, using the tommy bar. Then, release the pressure to 0. When the nut is released, and the hydraulic pressure is also totally released, the bolt will return to its natural length. This will be shorter than the extended length. During this step, you'll want to make sure that you record the release pressures for all the nuts in the overhaul report during this process. The pressure should be approximately the same as stated in the instruction manual or service letter. If the release pressure exceeds the engine manufacturer's maximum allowable, the bolt and nut must be renewed. Any bolt which had a release pressure of less than the final, 100% of tightening pressure, should be considered loose. The engineer can also use these release-pressure readings to better understand the condition of the bearing cap contact faces. It can assist in finding out how the studs may have been stretched or damaged during operation, and can also give indications of how well the engine was assembled last time. And, help to determine if the other bolts need to be checked at this time. Now that the nuts are unscrewed, recompress the jacks. So that they are ready for next time. This also keeps dirt out of the piston. Then, remove the jacks and spacers. The bottom end bearing keep and bearing shell can then be removed. Remove the nuts completely, and be careful not to damage the threads. Finally, remove the studs or bolts from the connecting rod. Earlier, you learned that you need to back off the jack by a 1/2 turn. Otherwise, you will not be able to remove the jack from the stud, when the hydraulic pressure is released. Take a look at what happens if you don't back off the jack. When the nut is released, and the hydraulic pressure is totally released, the stud returns to its natural length, which is shorter than its extended length. This creates a lot of pressure between the jack and the spacer pieces, resulting in so much friction that the jack cannot be removed. Let's reset. If we remember to back off the jack, and proceed to release the nut and hydraulic pressure, there will be a little bit of space between the jack and the spacer pieces. So that it can easily be removed. Make a practice of always backing off the jacks by a 1/2 turn. [SOUND OF ENGINE WHIRLING] [INSPECTING THE COMPONENTS] Now that you've fully disassembled the bottom end, you need to check the components before performing other tests and reassembling. The results of these inspections will vary according to the degree of care that has been taken with the components. Remember to always follow the maker's instructions carefully. The stud should be thoroughly cleaned and dried before close inspection under good light. Check for defects to threads, and visual signs of cracking and changes of bolt radii. The bolts must be renewed if there is any doubt as to the condition. Closely inspect the condition of the connecting rod, to establish if it can be allowed for reuse. Inspect the serrations of the meeting parts of the bearing keep and the connecting rod. A dull-gray color might indicate fretting. Next, you'll want to conduct a dye pen to check for cracks and other wear and tear. Thoroughly degrease using the cleaner. Remove the cleaner with an air hose which also removes any dirt particles. Apply red-dye penetrant liberally to all areas, and wait 10 to 15 minutes to allow the dye to penetrate any cracks. Then, thoroughly clean all traces of penetrant from the serrations. If you do not thoroughly remove all the visible red dye, you will confuse the results of this dye-pen check. Once the serrations are clean, apply white developer. Tell-tale red dye will show through the developer, indicating any cracks in the component. This connecting rod cannot be reused, and manufacturer's advice must be sought. Finally, closely inspect the contact surfaces, and the nut, and the bearing keep contact areas for fretting. Fretting found on any mating part may require reconditioning in a shore-side workshop. [SOUND OF ENGINE WHIRLING] [CHECKING FOR OVALITY - ASSEMBLY] Once you've inspected the individual components, the part of the overhaul will be to check the bearing housing for ovality. We want to verify that the degree of bearing nip will ensure that the designed area of bearing will take the distributed load. If ovality is present, the bearing shells will not fit correctly to the crank pin. It's important to account for correct clearances for lubricating oil thickness. In order to make this assessment, we need to reassemble the bottom end without the bearing shells. First, replace the bearing keep, leaving the shells aside. Lightly oil the threads, and then fit the bolts. Now, replace the bearing keep. At this point, we use a steel straightedge to make sure the bearing keep fits perfectly straight on the connecting rod, as serrating connecting rods and keeps have little sideway stability. Now, we need to tighten the nuts. Fit the spacers and jacks, and finally the hydraulic hoses. Compress the jacks, using the tommy bar. And, remember to back off the jacks by 1/2 turn during assembly, as well. Raise the pressure to 200 bar, and make sure the jacks cannot be moved or the hose connections rotated. Now, you need to tighten the nuts by hand, using the tommy bar, and raise the hydraulic pressure to the final figures stated in the manual or latest service letter. To do this, you need to ensure that the nuts are continuously and sequentially turned. Each movement synchronized with the pump strokes. Continue altering between the nuts, checking each one as moving in time with the hydraulic pump strokes. Tighten the nuts at the final pressure as stated in the manual or latest service letter, ensuring no greater force than sharp-positive pressure on the tommy bar. Release the hydraulic pressure slowly, ensuring the pressure drops to 0. Then recompress the jacks for later use. Now, we are ready to check the bearing housing for ovality. [SOUND OF ENGINE WHIRLING] [CHECKING FOR OVALITY - MEASUREMENTS] Use a micrometer to perform the measurements. It must be at the same temperature as the connecting rod, for readings to be accurate. Ensure that the inside of the bearing housing is undamaged and clean before starting. Remember, reliable readings take time. Only when the same readings are obtained, 3 or 4 times, can they be considered accurate. Ovality limits are very small, so take care to be precise. If the ovality is out of the limits, listed in the manual, the connecting rod will need to be landed for reconditioning. Reference the instruction manuals and service letters for full details and other checks that need to be made to the connecting rod at this time. [SOUND OF ENGINE WHIRLING] [REASSEMBLING FOR USE & DOUBLE-CHECKING TIGHTNESS] If you verify that the connecting rod is in acceptable condition, is can be reassembled with the bearing shells and refitted to the piston and engine. Disassemble the rod using the identical dismantling process referred to earlier. Then, carefully fit the bearing shells to the connecting rod and keep. Fit the keep back on the connecting rod, and fit the nuts hand-tight. Be sure to recheck the sideways alignment of the keep, using the steel straightedge. Fit the jacking equipment, always making sure that the nuts and the jacks move freely on the threads. Remember to back off the jacks by a 1/2 turn, before tensioning the studs. Raise the hydraulic pressure to around 200 bar. And tighten the nuts, using the tommy bar. Neither the jacks nor the hose connections will rotate, if the jacks are equally pressurized, and all components maintain good contact. Continue raising the hydraulic pressure to 50% of the final-stated pressure. Insert the tommy bar into one of the holes in the nut. Continue raising the hydraulic pressure, while rotating the nut, ensuring the nuts can be continuously and sequentially tightened. Again, each movement of the nut is synchronized with the pump strokes. Alternate between the nuts, ensuring each is moving in time with the hydraulic pump strokes. When the final pressure is reached, sharp, positive pressure on the tommy bar ensures the nut is tight. Release the pressure, and recompress the jacks. During the tightening process, the contact faces will have bedded in, so it is now necessary to recheck that you have tightened the nuts to the correct pressure by slackening the nuts, and immediately retightening them. Back off the jacks by 1/2 a turn. And, reapply full hydraulic pressure. When the same tightening pressure is achieved, slacken the nuts with the tommy bar. Again, do not use force to do this. It may be necessary to increase the hydraulic pressure very slightly, until the nut comes loose. Once loosened, adjust the hydraulic pressure, if necessary, and retighten the nuts using the tommy bar, using sharp, positive pressure. Finally, release the pressure and recompress the jacks, before removal, to ready them for the next time. The bottom has now been inspected, and is ready to be refitted into the engine. You can use this simple technique to ensure that the nuts do not slacken off during running. Make sure you check the service letter. And, to see if retightening is required after a prescribed engine-running period. This will help maintain the component-contact faces in the best condition before the next overhaul. [MUSIC] Now, you know how to apply the correct technique, when inspecting the connecting rods bottom end. By being cautious in overhauling this critical component, you reduce the chances of engine damage or failure. Saving substantial delay in repair costs. And, more importantly, you are keeping you and your fellow seafarers safe on your voyage.

Video Details

Duration: 13 minutes and 39 seconds
Country:
Language: English
License: Dotsub - Standard License
Genre: None
Views: 6
Posted by: maritimetraining on Aug 21, 2019

Engine Maintenance_Connection Rod Bottom End_Merge(1)

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