“That is an excellent way to determine the amount of work the engines have done,” says Ellison. “As you go up into the high horsepower markets, they generally always go by fuel consumption.” An engine that runs at 80% of full power all of the time will generally need an overhaul before one that is running in an application with a 40% duty cycle.
“Keeping accurate, up-to-date records and monitoring engine performance are effective ways to determine engine health,” adds Hanks. Routine oil and coolant sampling and analysis are also useful. “Oil samples are valuable in monitoring engine health, but indications of ‘critical’ wear could be one-time events and should be viewed with objectivity. Many parts of an engine can contribute to wear metals in the oil, so oil analysis should be considered one piece of a diagnosis puzzle used to narrow down areas of potential failure.”
Another piece of the puzzle is a compression test, which can be useful for checking the condition of the cylinders. “Anything more than about a 10% to 15% difference between cylinders indicates something is different between the sealing components in the low cylinder compared to the good cylinder,” says Ellison.
It is important to note that compression specifications can vary between engine makes and models. “When performing an engine compression test, it is important to reference the respective factory workshop manual for proper procedures, specifications and allowable limits,” says Urso. Kubota Engine America suggests compression variances between cylinders should remain under 10%.
The most recent engine control units allow simplified compression tests. “With new engine controllers, there are two options for testing compression: a relative compression test and an actual compression test,” says Hanks. “A relative compression test monitors engine speed through the sensors on the crankshaft and shows relative compression by comparing deceleration and acceleration of the crankshaft as each piston rises on the compression stroke.”
The relative test can only monitor differences between cylinders and not an actual value. “Many newer machines with engine controllers have the capability to test relative compression through a user interface such as John Deere’s Service ADVISOR,” Hanks notes. “An actual compression test measures dynamic pressure and may be performed using a gauge to determine compression of an individual cylinder. A number of manufacturers provide a minimum specification for cylinder performance.”
There are other ways to gauge cylinder health. “One thing I have found to be more useful than a pressure test is a leak-down test,” says Ellison. “You pressurize the cylinder and there is actually a gauge that will tell you what percent leakage it is. The beauty of the leak-down tester is you can actually listen for where the leakage is — whether it is going into the crankcase or coming out of an exhaust or intake valve. That helps identify what might need some attention.”
There are many tools available for inspecting the cylinder bore without disassembling the engine, including borescopes. “Usually, simple mechanical checks for blow-by and valve lash will prove just as effective as disassembling the engine,” says Hanks. “On newer machines, John Deere dealers can utilize Service ADVISOR to perform diagnostic tests that eliminate the need for many mechanical checks. Disassembling and reassembling the engine hardware is normally the last option. A typical approach is to monitor routine oil and coolant analysis.” ET