Learn more. How are compression rings lubricated? Ask Question. Asked 3 years, 5 months ago. Active 1 year ago. Viewed times. How is the compression ring then lubricated and kept from scoring the walls? Improve this question. Erik Erik 2 2 silver badges 12 12 bronze badges. During deceleration when cylinders experience low vacuum conditions, some oil is sucked pushed past the oil scraper ring into the comp rings. Add a comment. The film thickness is kept minimal by a so called oil control ring.
This ring is situated beyond the piston rings so that the surplus of oil is directly scraped downwards to the sump. The oil film left on the cylinder wall by the passage of this ring is available to lubricate the following ring. This process is repeated for successive rings. On the up stroke the first compression ring is lubricated by the oil left behind on the cylinder wall during the down stroke. This is the reason why, despite of frequent replenish of oil, oil change remain essential or even become more essential.
Cams and followers. An oil pump is located on the bottom of the engine, at the left of the figure. The pump is driven by a worm gear off the main exhaust valve cam shaft. The oil is pumped to the top of the engine, at the right, inside a feed line. Small holes in the feed line allow the oil to drip inside the crankcase. In the figure, we have removed the fuel system and peeled back the covering of the crankcase to see inside.
The oil drips onto the pistons as they move in the cylinders, lubricating the surface between the piston and cylinder. The fact that the surface of the seizure areas has an almost pure metallic finish indicates that the oil film was present but significantly weakened at the time of the seizure.
Due to the limited extent of the damage, this concerns a temporary lack of oil or the early stages of damage. The damage would have been even more severe if engine had been operated further. NOTE With this type of seizure due to lack of lubrication, the damage area is always located in the area of the piston skirt where the normal wear pattern would have formed on an undamaged piston after running in.
This is a typical example of seizure due to lack of lubrication. It usually occurs on the pressure side and is less common on the anti-thrust side. This damage is caused when the lubricating film breaks down on only one half of the cylinder. It is caused either by a lack of lubrication within a locally confined area or by the affected side of the cylinder overheating.
Lack of clearance can be excluded as the potential cause here as, despite the severity of the seizure marks, there are no wear marks on the opposing counter-side. Narrow, sharply defined longitudinal friction marks on the piston skirt instead of the normal piston wear pattern. Unburned fuel has condensed at the cylinder running surface and diluted or washed off the load-bearing oil film. As a result, the interacting sliding parts piston and cylinder bore run dry against each other, which results in long, narrow friction marks.
The piston ring zone usually remains undamaged. NOTE In the case of damage caused by unburned fuel, the damage occurs at the load-bearing areas on the piston skirt. These are the points at which the normal wear pattern would have formed on an undamaged piston. Due to a fault on the injection nozzle, non-atomised fuel was able to reach the cylinder wall, where it weakened the oil film to the point where the piston was running dry without any lubrication at all.
As a result, the piston top land seized so severely that it was temporarily welded to the cylinder wall. This caused chunks to be torn from the piston head. This type of damage primarily occurs during the running-in phase under heavy loads, when the piston rings are not yet run in and hence do not yet provide a full seal mostly on diesel pistons. The combustion gases streaming past the piston rings heat up the rings and the cylinder wall excessively and cause the oil film to break down.
However, abnormal combustion and increased temperatures or insufficient cooling of the piston and cylinder wall can also affect or even destroy the lubricating film. Initially this causes the piston rings to run dry without lubrication, causing burn spots.
The piston also has to slide over the non-lubricated parts of the cylinder, which causes initial rubbing marks on the piston top land and subsequently leads to seizures on the entire piston skirt Fig. What do we mean when we talk about seizure caused by a lack of clearance? What causes dry running between the pistons and the cylinders? Why is the Motorservice Group uses cookies saved to your device in order to optimize and continuously improve its websites, as well as for statistical purposes.
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