Oft quoted, and used to misinform often, but here's a paper that states it.
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/26638/0000180.pdf
Will try to dig up the other mentioned papers.
Quote:
The cylinder may wear more at TDC than elsewhere [l - 41 but there is measurable wear all over. The piston rings rather than the piston are the main cause of cylinder wear. There is higher wear at TDC than elsewhere because it is the location of the highest contact pressure, the location of the greatest concentration of acids and the location of the thinnest lubricant film. On the latter point, there have been several attempts to calculate [ 5 - 81 and measure [4, 9, lo] the lubricant film thickness between piston rings and cylinder wall.
The film thickness beneath the top compression ring at TDC was found to be very small, in the range 0 - 3.0 pm, because of the low sliding velocity at that location. The maximum oil film thickness was found near the center of the stroke where the maximum speed is reached. This applies, of course, to the condition of normal running. All engines that stop and start do so with very thin lubricant films at all locations. For per- spective on the influence of oil films, Gumbleton [ll] found that 75% of the total wear which took place during a 2 h run occurred in the first 6 min. Cylinder wear in the progressive stage may occur by several mechanisms but mostly by abrasion and corrosion. Some abrasive wear is caused by par- ticles left in the engine during manufacture and assembly [12]. This is cor- rectible by proper cleaning during the various stages of manufacture [13]. A form of abrasion may result from debris accumulated from various wear mechanisms. However, dust from the intake air or dirt in the lubricating oil probably causes most of the abrasive wear.
Corrosion was found by Williams [14] to be important, particularly under cold-running conditions, i.e. when the products of combustion con- densed on the cylinder walls. The acidic condensate causes high wear rates by corrosion [15 - 171. This mode can be reduced by using thermostats so that engines spend less time running at low temperatures and by the use of acid-buffered lubricants [ 18, 191.
A mechanism of wear by formation and removal of oxides should also be included in the list. This mode of wear is seen in the wear of lubricated steel but it has not been reported to occur in engines. 2.3.
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/26638/0000180.pdf
Will try to dig up the other mentioned papers.
Quote:
The cylinder may wear more at TDC than elsewhere [l - 41 but there is measurable wear all over. The piston rings rather than the piston are the main cause of cylinder wear. There is higher wear at TDC than elsewhere because it is the location of the highest contact pressure, the location of the greatest concentration of acids and the location of the thinnest lubricant film. On the latter point, there have been several attempts to calculate [ 5 - 81 and measure [4, 9, lo] the lubricant film thickness between piston rings and cylinder wall.
The film thickness beneath the top compression ring at TDC was found to be very small, in the range 0 - 3.0 pm, because of the low sliding velocity at that location. The maximum oil film thickness was found near the center of the stroke where the maximum speed is reached. This applies, of course, to the condition of normal running. All engines that stop and start do so with very thin lubricant films at all locations. For per- spective on the influence of oil films, Gumbleton [ll] found that 75% of the total wear which took place during a 2 h run occurred in the first 6 min. Cylinder wear in the progressive stage may occur by several mechanisms but mostly by abrasion and corrosion. Some abrasive wear is caused by par- ticles left in the engine during manufacture and assembly [12]. This is cor- rectible by proper cleaning during the various stages of manufacture [13]. A form of abrasion may result from debris accumulated from various wear mechanisms. However, dust from the intake air or dirt in the lubricating oil probably causes most of the abrasive wear.
Corrosion was found by Williams [14] to be important, particularly under cold-running conditions, i.e. when the products of combustion con- densed on the cylinder walls. The acidic condensate causes high wear rates by corrosion [15 - 171. This mode can be reduced by using thermostats so that engines spend less time running at low temperatures and by the use of acid-buffered lubricants [ 18, 191.
A mechanism of wear by formation and removal of oxides should also be included in the list. This mode of wear is seen in the wear of lubricated steel but it has not been reported to occur in engines. 2.3.
