Gil Consumption Analysis
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1. Oil Consumption
Analysis
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2. This program will discuss the causes for oil consumption. The extent of the oil consumption and the condition of the angina should be discussed with the aparatar.
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3. Before any angina work is performed, check ter: . External oil leaks . Check the oil level, and dipstick marking . Check the coolant level . Check the juba oil and air filter maintenance records . Check the condition of the intake air system and the air compressor for oil carry-ovar problems. Air compressor oil carry-ovar can be checked by draining the air tank and checking for excessive oil in the air system. After correcting any external leak problems the angina must be operated, using a multi-grade oil for 5000 miles or 30 days and the oil consumption verified.
4. After verification of oil consumption, greater than the published ratas, using multi-grade oil, disassemble the angina and inspect the internal angina components. Wet exhaust ports could be causad by excessive idling and this is not a good indication of oil consumption. The time-in-service is a factor in determining wear of internal angina parts. (Referenea - Adjustment Practicas and Schedules - Subiect 3.1, Pagas 1, 2, 3 and 4).
~ Copyright
@ 1980
By Cummins
Engine
Company, Inc. 1
5. The wear factors are:
contributing
to oil consumption
A. Abrasive wear
due to grit from unauthorized honing, compression ring chrome flaking, or dirt either built into the angina or entering through the air intake system.
B. Adhesive wear due
to scuffed or scored pistons and rings, oversize pistons and rings, undersized liner bares, or angina overheating. These dimensional problems, as well as damage from improper test run-in procedures, will result in early angina failure. C. Corrosive wear due to extended oil drain intervals, or the use of high sulfur fuels.
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6. A visual inspection of the piston and ring assemblies and the condition of the liner bares at the ring travel area will assist in the oil consumption analy~is. The first things to note are the condition of the pistons and rings and the manner in which the rings are assembled on the piston. If the rings haya not been properly installed, they will not function correctly and could be the cause of the problem.
7. Improperly installed or upside-down intermediate rings exhibit polished wear bands separated by a black area on the ring faca. Properly installed intermediate rings will haya polished wear bands which are on adjacent sides. This upside down installation will cause the ring to scrape oil up toward the combustion chamber, not down the cylinder wall as it should when properly installed.
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8. Excessive carbon build-up on the piston crown and ring lands is evidence of oil passing the rings and entering the combustion area. This build up may also indicate thermal breakdown of the lubricating oí!.
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9. These piston deposits can cause a loss of oil control by preventing the combustion gases from properly seating the compression rings in their grooves. The deposits may also lead to liner bore polishing and scratching.
10. The seating pattern on the ring faca should also be observad. This ring set shows a typical seating pattern for an angina having good oi! control after 7,000 miles of operation. . The top compression ring shows a seat pattern at the crown of the barrel faca. . The first intermediate or second ring is a 2° tapar faced ring which shows a seat pattern at the bottom of the ring faca. The second intermediate or third ring is also a 2° tapar faced ring which shows a seat pattern at the bottom of the ring faca. The oil control ring shows both rail lands seating squarely with the liner bore. These are excellent seating patterns on all ring faces.
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11. These rings show excessive wear from abrasives. The top compression and first intermediate rings are worn to a full faca contact. The discoloration on the top ring faca is the result of applying a copper sulfate solution to check for the absence of chrome. This illustration indicates that the chrome has been completely worn away at the ring gap. Although not clearly shown, the second intermediate and oi! rings haya vertical scratches causad by abrasives.
12. This ring set shows scuffing of all rings. Examples of this scuffing could result from carbon packing in the ring grooves, improper maintenance of the cooling system or a lack of lubricating oi!. Continuad operation under these conditions could result in seized pistons and angina failure.
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13. These top compression rings are shown to denote different faca wear patterns. The upper ring is new. The cantar ring has a good cantar crown seating pattern. The lower ring is worn to a full faca contact. Note the absence of chrome at the ring gap.
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14. This top compression ring illustrates chrome flaking. As top compression rings wear to full faca contact, the chrome plating becomes very thin or may be worn through to the base metal. Continuad operation will result in chrome chipping off at the ring faca edge and, if excessive, could lead to a loss of oil control and scratched liners. ~-""'"
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15. This chrome plated top compression ring shows excessive "chaining" on the bottom side of the keyslona angla. The shiny bands (chaining) illustrated are due to abrasive particles being trapped between the piston ring groove and the ring. These abrasive wear conditions are usually a sign of improper air intake system maintenance.
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16. These second rings (first intermediate) are shown for a comparison of the faca wear patterns. The upper ring is new. The cantar ring exhibits a good wear pattern, and the lower ring is worn to full faca contact, usually a result of abrasive wear.
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17. Face wear patterns for the third ring (second intermediate) are illustrated here. The upper ring is new. The cantar ring shows the desired lower faca wear pattern. The lower ring also shows a lower faca wear pattern, due to abrasives, extending ovar approximately 80% of the faca surface.
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In this
view showing oil control ring comparison, the upper ring is new and the cantar ring shows the desired wear pattern. Note the discoloration due to the application of copper sulfate solution on the lower ring, indicating wear completely through the chrome. This illustration, like the physical parts, does not reveal the extent or pattern of wear to enable visual failure análysis. New ring raíl widths vary from .012 to .019 inch; therefore, determining the extent of actual wear after use is not possible.
19. This illustrates oil control ring expander embedment. A visual examination of the expander seating area may show an outline of the expander. However, the extent of embedment may be determinad by passing a pencil point ovar the expander seat pattern and sensing the depth of the grooves. Expander embedment may cause ring element lock-up, not allowing expansion and contraction of the raíl faca to the liner bore surface.
20. An overlapped oil ring expander will cause low oil ring tension, resulting in a loss of oil control. Note the shiny portions on three end-gap "huddles" where the black oxide coating has been worn away due to excessive contact with the oil ring and piston ring groove.
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cylinder liner shows severe streaking with a lubrite over-etch condition in the streaks. This condition was evident on some engines built before June, 1978. Over-etching caused rapid ring face wear at low mileage.
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22. In this example we see a scored bore surface. Scbring is actually vertical grooving in the liner bore. If scores run the full length of the bore, they may be caused by: . A progression from piston ring scuffing. "Four point" piston scoring due to overheating. Improper cold starting practices. . Rings, piston groove lands, or ni-resist inserts that are broken. Dirt entering the engine through the air intake system. If scoring is found in the lower part of the bore, the problem may be due te: Improperly installed liner crevice seals or packing rings. Distortion of the cylinder block lower liner bore.
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23. To prevent oil consumption and possible early engine failure after rebuild, do not reuse damaged liners or liners that are worn more than the specified worn limit. 80th new and used liners and pistons must be thoroughly cleaned and inspected, as described in the engine shop manual, before installation.
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. 24. A cross section of the tour current NH/NT Series Engine piston rings are shown to provide visual id entification for assembly. For good oil control the three upper rings must be installed with the top-side-up.
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25. The top compression
ring is a barrel faced keystone ring with a .004 to .007 inch chrome plating on the faca. New rings are either ink stamped "top", or haya a small notch cut in the top surface at the end gap.
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26. 80th the first and second intermediate rings feature a 20 tapered faca. The first intermediate ring has a notched back that allows the cylinder pressure to seal the ring more firmly at the faca. 80th of these rings haya a tiny groove machined into the faca surfaca, near the top edge, for installation identification.
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27. The oil control
ring has parallel sides, and may be with either side up with the expander gap
installed located 1800 from the ring gap.
28. Piston rings installation. rings should described in
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should not be over-expanded during To avoid over-expanding, all piston be installed with a ring expander, as the angina shop manual.
29. When properly installed on the piston, the rings should: . Be installed with the ring gaps staggered as shown, . And be thoroughly lubricated before being installed in the cylinder liner.
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30. To reduce the rata of oil contamination and sludge, varnish, and oxidation build-up on pistons and other critical components, Cummins Engine Corijpany, Inc. recommends the use of a high-quality multigrada lubricating oi!. (Reference - Lubricating Oils For Cummins Engines, Service Bulletin No. 3379002-04).
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31. Scheduled maintenance and proper are both essential for the satisfactory these components.
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angina run-in service lita of
" 32. The information contained in this program should establish guidelines by which the cause or causes of excessive oil consumption may be determinad.
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Cummins Engine Company, Ine. Columbus, Indiana Bulletin No. 3387148-R Printed in U.S.A. 7/80
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