Is Your Engine Healthy? Some factors for evaluating your engine's condition

Nov. 1, 2001

Is Your Engine Healthy?

Some factors for evaluating your engine’s condition

By Textron Lycoming

November 2001

As an engine builds operating hours and approaches TBO, which may be either the manufacturer’s recommended operating hours, or a calendar year limit before overhaul, the question arises concerning the decision to either continue flying, or top overhaul, major overhaul, or exchange engines. The following nine points can help make that decision.

Oil consumption
The operator and maintenance personnel should know what has been the general history of oil consumption during the life of an engine.
A possible danger signal concerning engine health is a definite increase in oil consumption during the recent 25 to 50 hours of flight time. The oil screens and filter should be carefully observed for signs of metal. Maintenance should also take a good differential compression check at this time. They should also look in the cylinders with a gooseneck light or a borescope to detect any unusual conditions in the combustion chamber.
If you haven’t looked at your air filter lately, it would be a good idea to carefully inspect it for wear and proper fit. This is all the more important when operating in dusty areas, and definitely could be a cause of increased oil consumption.

Engine history and calendar age
If a powerplant has been basically healthy throughout its life, this would be a favorable factor in continuing to operate it as the engine approached high time. Alternately, if it has required frequent repairs, the engine may not achieve its expected normal life. The engine logbook should contain this accumulative record.
Another important aspect of an engine’s history would be its calendar age. Engine flight time and calendar age are equally important. We have observed that engines infrequently flown do tend to age or deteriorate more quickly than those flown on a regular basis. Therefore, Textron Lycoming recommends both an operating hour limit and a calendar year limit between overhauls. Service Instruction 1009 gives these recommendations, but other items in this checklist will help to determine if an overhaul or engine exchange is needed before the engine reaches these recommended limits.

Pilot’s opinion of the engine
The pilot’s opinion of the powerplant based on his experience operating it is another important point in our checklist. He will have an opinion based on whether it has been a dependable powerplant, and whether or not he has confidence in it. If the pilot lacks confidence in an engine as it approaches the manufacturer’s recommended limits, this could be a weighty factor in the decision to continue flying or to overhaul it. He should consult with his maintenance personnel concerning their evaluation of the condition of his powerplant.

The basic question here would be how the engine has been operated the majority of its life. Some engines operating continuously at high power, or in dusty conditions, could have a reduced life. Likewise, if the pilot hasn’t followed the manufacturer’s recommendations on operation it may cause engine problems and reduce the expected life. This becomes a more critical influence on a decision in single engine aircraft, and also for single- or twin-engine planes flown frequently at night or in IFR conditions.

Good maintenance should aid in achieving maximum engine life; alternately, poor maintenance tends to reduce the expected life. We notice among those powerplants coming back to the factory for rebuild or overhaul, that the smaller engines in general have had less care and attention, and in a number of instances have been run until something goes wrong. The higher powered engines have generally had better maintenance and show evidence that the operators do not wait until something goes wrong, but tend to observe the manufacturer’s recommended operating hour or calendar limits to overhaul. The engine logbook should properly reflect the kind of maintenance provided the engine or engines. The technician who regularly cares for an engine will usually have an opinion about it’s health.

What does the oil tell?
Clean oil has consistently been an important factor in aiding and extending engine life. A good full flow oil filter has been a most desirable application here. When the filter is exchanged, it should be opened and carefully examined for any foreign elements, just as is accomplished at oil change when the engine oil screen is also examined for the same purpose. Just as the spark plugs tell a story about what is going on in the engine, the engine oil screen and the external oil filter tell a story about the health of an engine. Whether the engine is equipped with an oil filter or just a screen, oil changes should have been accomplished in accordance with the manufacturer’s recommendations. These oil changes should have been recorded in the engine logbook.
If oil is analyzed, it should be done at each oil change in order to establish a baseline. Analysis is a tool which only gives useful information when a dramatic departure from the established norm occurs.

Compression checks
What has been the trend in compression in at least the last two differential compression checks? The differential compression check is the more reliable type and should be taken on a warm engine. If the differential check reveals 25-percent loss or more, then trouble may be developing.
A compression test should be made anytime faulty compression is suspected, anytime the pilot observes a loss of power in flight, when high oil consumption is experienced, or when soft spots are noticed while hand pulling the prop.
Many maintenance technicians do a compression check at each oil change, and it is also considered part of the 100-hour engine inspection and the annual inspection. Most experienced maintenance personnel feel that the differential compression check is best used to chart a trend over a period of flight hours. A gradual deterioration of charted compression taken during maintenance checks would be a sound basis for further investigation.

Spark Plugs
The spark plugs when removed and carefully observed, tell the skilled mechanic what has been happening in the cylinders during flight, and can be a helpful factor in deciding what to do with a high time engine:

  1. Copper run out and/or lead fouling means excessive heat.
  2. Black carbon and lead bromide may indicate low temperatures, the type of fuel being used, and possibly excessive richness of fuel metering at idle.
  3. Oil fouled plugs may indicate that piston rings are failing to seat, or excessive wear is taking place.
  4. The normal color of a spark plug deposit is generally brownish gray.
  5. In high compression and supercharged engines, a cracked spark plug porcelain will cause or has been caused by preignition.

Engine manufacturer’s recommended overhaul life
Service Instruction 1009 is the Textron Lycoming published recommendation for operating hour and calendar year limits until engine overhaul as they apply to each specific engine model. The amount of total operating time on an engine will be a basic factor in any decision to either continue flying, change, top, or major overhaul the powerplant. Operators should be reminded, however, that the hours of service life shown in the service instruction are recommendations for engines as manufactured and delivered from the factory. These hours can normally be expected provided recommended operation, periodic inspections, frequent flights, and engine maintenance have been exercised in accordance with respective engine operator’s manuals.
If an operator chooses to operate an engine beyond the recommended limits, there are factors to consider. The cost of overhaul is likely to be greater as engine parts continue to wear, and the potential for failure may also increase.
Operators who have top overhauled their engine at some point in the engine life invariably want to know if this extends the life of the engine. This is an important question. The chances are that if the operator applies the checklist we have been discussing and comes up with favorable answers to these questions about his engine, he can probably get the hours desired — with only a few exceptions. But, a top overhaul does not increase the official life or TBO of the engine.
We are surprised from time to time to have owners tell us they top overhauled their engine at some point less than the major overhaul life for no reason other than somebody said it was a good idea. Unless the manufacturer recommends it, or there is a problem requiring a top overhaul, this is a needless cost. If the engine is healthy and running satisfactorily, then leave it alone!
One other point deserves attention here; there is no substitute or cheap route to safety in the proper maintenance or correct overhaul of an engine.

Apply all of these basic nine points concerning your engine or engines and then make a decision whether to top overhaul, major overhaul, exchange engines, or continue flying.
Because the failure to look for metal in the screens and filter, or ignoring what is found, can lead to catastrophic engine failure, we’ll attempt a logical approach to the proper action to be taken when metal shows up in the oil screen or oil filter cartridge.

Editors note: Inspecting for oil particulates is a good way to monitor the health of an engine. The following discusses some suggestions from Textron Lycoming pertaining to evaluation of metals found in engine screens or filters.

General information

  1. DON’T PANIC on small amounts of shiny flakes or small amounts of short hair-like bits of magnetic material. Experience has shown that engines are sometimes pulled unnecessarily.
  2. DON’T PANIC if it’s a low time engine. A few bits of metal left from manufacturing are not too uncommon in the oil screen or filters on new, rebuilt, or overhauled engines.
  3. DON’T PANIC. Again if it’s a low-time engine, it may be a replacement for one that had previously suffered a structural failure. The metal may have just been dislodged from some hiding place in the oil cooler, oil lines or oil tank.
  4. Item 3 brings up the importance of properly cleaning all items transferred from a failed engine to a replacement engine. On dry sump engines, don’t overlook cleaning of the oil tank. Oil coolers and oil lines should be cleaned by a proven method, or replaced.
  5. In some rare cases where the pleated cylindrical type oil screen is used, the screen itself may be making metal. Closely inspect the end of the internal relief valve ball. If the ball is deformed, this may be the culprit. Replace the screen assembly.

The following information was taken from Textron Lycoming Service Instruction No. 1492C. It discusses oil filter/screen content inspection for the affected model engines.

Oil filter/screen content inspection
NOTE: To insure that no external contaminants enter the oil filter/ screens, use clean containers for collecting oil; and perform inspections on clean surfaces.

  1. For engines employing a pressure screen system, remove the screen and check for metal particles.
  2. . Using approved method (e.g., for full flow, spin-on filters, use Champion Tool CT-470 or Airwolf Cutter AFC-470), open the filter.
  3. Check the condition of the oil from the filter. Inspect for a high concentration of aluminum in the oil, indicated by a shining, metallic residue.
  4. After draining oil, remove the suction screen from the oil sump and check for metal particles.
  5. Remove the paper element from the filter.
  6. Carefully unfold the paper element and examine the material trapped in the filter.
  7. When performing the regular filter/screen inspection, check for premature or excessive wear of piston pin plugs, indicated by the presence of metal particles, shavings, or flakes.
    NOTE: In new or newly overhauled engines, some small particles of metallic shavings might be found, but these are generally of no consequence and should not be confused with particles produced by impacting, abrasion or pressure.
  8. Evidence of metal contamination found in the filter element or screen requires further examination to determine the cause. Below is a list of recommended actions based on the appearance and approximate quantity of particles.
    1. Five or fewer small (1/16-inch diameter or less) pieces of metal — place aircraft back in service and check oil filter or screen at next scheduled oil change/oil filter replacement.
    2. 10 to 20 small (1/16-inch diameter or less) pieces of shiny flake-like, nonmagnetic, or 10 or fewer short hair-like pieces of magnetic material — place engine back in service and again check oil filter or screen in 25 hours.
    3. 20 to 40 small pieces as in step b. — place the aircraft back in service and check oil filter or screen at the next 10 hours.
    4. As in step b, but larger amount, such as 45-60 small pieces — change filter or clean screen, drain oil, and refill. Run engine on ground for 20 to 30 minutes. Inspect filter/screen. If clean, fly aircraft for 1 to 2 hours and again inspect filter/screen. If clean, inspect filter/screen after 10 hours of flight time.
      NOTE: In items e. through j. below, the engine should be removed from service until the source of the metal is determined and corrective maintenance has been accomplished.
    5. Pieces of metal ranging in size of broken lead pencil point or greater. Remove suction (sump) screen to check for pieces of metal that may have fallen into the sump. In any event, ground aircraft and conduct investigation. A mixture of magnetic and nonmagnetic material in this case often times means valve or ring and piston failure. Removing bottom spark plugs usually reveals the offending cylinder.
      f. Nonmagnetic plating averaging approximately 1/16-inch in diameter; may have copperish tint. Quantity found — 1/4 teaspoonful or more; ground aircraft and investigate.
    6. Same as in step b, but may be slightly larger in size and minus copperish tint. On direct drive engines, propeller action may be impaired. Ground aircraft and investigate.
      h. Nonmagnetic metal brass or copperish colored. Resembles coarse sand in consistency. Quantity of 1/4 teaspoonful or more — ground aircraft and investigate.
    7. Anytime metal is found in the amount of 1/2 teaspoonful or more, it is justification for engine removal.
    8. If any single or several pieces of magnetic or nonmagnetic metal larger than previously mentioned are found, ground aircraft.
      Note: If the origin of the metal contamination cannot be determined, a call may be made to the Textron Lycoming Product Support Department. A good description of the metal may result in placing its origin. When phoning Textron Lycoming or when returning metal removed from engines, supply the complete engine model designation, serial number, history of engine, oil temperatures, oil pressures, and any unusual behavior of the engine on the ground or during flight. Do not ship material to Textron Lycoming without first calling the Product Support Department.
  9. If examination of the oil filter or screen indicates abnormal aluminum or iron content, contact a technical representative or the Textron Lycoming Product Support Department.

Warranty for the metal analysis is available for engines listed under Models Affected only if the engine from which the sample is taken is a new, remanufactured, or overhauled engine from the Textron Lycoming factory.

This article was reprinted with permission from Textron Lycoming’s Flyer and Service instruction 1492C. For questions on your Textron Lycoming engine, you can contact their Product Support Department at 1-800-258-3279, or visit their website at