TECHNICAL INFORMATION BULLETIN
OCTOBER 16, 2002
797B (JSM) OFF-HIGHWAY TRUCKS
Component Code 1000
SUBJECT: EXCESSIVE WEAR IN THE 3524 ENGINES IN 797 OFF-HIGHWAY
There have been several reports of dirt ingestion on 797 Trucks that is causing premature engine wear. Engine dirt ingestion can be a result of the following problems:
· Leaking air intake piping before or after the turbochargers
· Inadequate air filtration
· Poor maintenance of the air system
· Dirt entry during an engine repair that requires the engine to be opened up
The Wear Metal Limit Table for 797 Off-Highway Trucks is available to S∙O∙S Services lab personnel and Dealer Service Managers. This Wear Table was derived from 797 Trucks operating in North America. Please be aware that these Wear Tables do not reflect the wear level limits for engines using an Oil Renewal System (ORS). It is very important to trend fluid compartments during the complete life of the machine and not just the last one or two samples. Many sites look at either the last, or even the last few samples when looking for abnormal trends in wear elements. This method does not always tell the whole story. Critical changes in wear elements that occurred earlier in the engines life may be missed. Graphing and reviewing the complete S∙O∙S Oil Analysis History of an engine is the best method to trend changes that can lead to catastrophic failures that cause unscheduled downtime. When you graph the results of the S∙O∙S Oil Analysis for the complete life of the machine, you can tell if there is a steady trend upward, or if an increase in a wear element is just a one-time occurrence where someone was in the engine to do work. See the examples that follow:
Illustration 1 shows a graph of the results of the S∙O∙S Oil Analysis for the Front Engine in a 797 Truck that experienced severe dirt entry at about 500 engine hours. The dirt entry resulted in a significant iron increase and a much smaller aluminum increase. Aluminum can come from the piston skirt or it can be part of the dirt ingestion. Many soils contain significant amounts of aluminum as well as silicon. The front engine in this example experienced severe cylinder pack wear that resulted in high blow-by and high oil consumption.
Illustration 2 shows a graph of the results of the S∙O∙S Oil Analysis for the Rear Engine in the same 797 Truck. This engine had a more normal trend analysis. There was a slight increase in iron levels at 600 engine hours. However, this iron increase was caused by higher levels of soot in the oil and not caused by dirt entry.
Illustration 3 shows a graph of the results of the S∙O∙S Oil Analysis for the Front Engine in a 797 Truck that experienced moderate dirt entry at about 1500 engine hours. As seen in the previous example, the iron levels are increasing as the silicon level increases. There is also a slight increase in aluminum values. The iron increase at 600 hours was caused by high soot and not by dirt entry.
Illustration 4 shows a graph of the results of the S∙O∙S Oil Analysis for the Rear Engine in the same 797 Truck. The Rear Engine had a slight iron increase from 600 to 900 engine hours. This iron increase was again caused by soot and not caused by dirt entry. The silicon and aluminum trends for this engine are low and stable.
In the previous examples, soot was mentioned as a cause for high iron wear. High soot can be caused by a number of factors including the following:
· Plugged air filter
· High restriction in the air system
· Operation at high altitude
· Retarded injection timing
· Failed or damaged turbochargers
Soot readings may also change depending on the operating conditions at the job site. Engines that go through many acceleration cycles may produce more soot than engines that operate on long steady hauls.
Soot is not listed on the Wear Tables. It is recommended that the soot be kept below 120 percent or you may experience accelerated engine wear. Follow the recommendations for oil condemning that are provided in "Optimizing Oil Change Intervals", PEDP8025. Cat oil or a premium grade API approved CH-4 or CI-4 oil should be used to maximize engine component life.
The Wear Tables do not show guidelines for sodium or potassium. Coolant leaks in the engine can generally be identified by signs of sodium and/or potassium in the oil sample depending upon the coolant being used. Each application is different and the type of leak will determine how quickly you will see traces in the oil. Internal coolant leaks, where a gasket failure allows coolant to directly enter the oil in the crankcase, will generally show higher levels than a leak entering the air system. It is important that you document the trend of your engine. Then, when you see a sudden change from the norm, you need to react.
On the 3524 Engine, it is recommended that once the sodium or potassium level reaches 15 to 20 PPM you should start looking for an internal coolant leak in the air system. Levels that are allowed to reach 200 to 300 PPM will affect bearing life. If you see smaller increases of sodium or potassium with corresponding increases in iron or chrome, you should start looking for a coolant leak in the aftercooler. Use a borescope to inspect the lower aftercooler housing to see if the aftercooler is leaking. If you see discoloration on the sides of the housing and coolant traces lying in the bottom, then the aftercooler is probably leaking. If you remove the top right hand rocker base bolt, you can insert a borescope through the hole for the bolt. This will allow you to look at the intake passage. You may find cracks in the intake passage of the cylinder head. Coolant discoloration and excessive cooling system pressure generally indicates a head gasket leak that is allowing combustion gasses to enter the cooling system. These are just a few examples of coolant leaks and the ways they were found.
A well-established S∙O∙S Services Oil Analysis Program will provide the following benefits:
· Reduce the amount of unscheduled downtime
· Allow customers to get the most out of their oil
· Increase the life of major components in the engine
In the examples above, the importance of frequent oil sampling is clearly shown. A dirt entry problem can severely damage an engine in less than 500 hours. Therefore, oil samples should be taken every 250 hours or less. For best results, a weekly or 150 hour sampling schedule is recommended. If you need additional information on S∙O∙S Services or trend analysis, contact our regional S∙O∙S Services Coordinator. The coordinators are listed in the Cat Dealer Intranet sites under S∙O∙S Services/Contacts.
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