NOTE: The following test procedure is a generic version of the one used by Marvel and Scott to measure oil volume pumped to the rocker boxes of Lycoming parallel valve engines. It has been generalized for this WEB page to aid in its use for most engine/airframe combinations.

1. Read and understand these instructions PRIOR to starting the test! You should obtain an 11/16 inch wrench (larger one needed for O-320H and O-360E), four (or six) metal one-quart cans (rectangular, not round), four (or six) Lycoming oil return tubes cut down to about two inches in length, hose segments long enough to connect each of these tubes to the cans that will be duct taped to the inside of your cowling, a roll of duct tape, and a device for measuring the collected oil volume in cubic centimeters. Use a marking pen to label the cans 1 through 4 (or 6) as appropriate for your engine. If you cannot obtain the Lycoming tubes, you can probably just use a hose whose inside diameter fits directly over the cylinder head fitting and use a hose clamp to hold it in place.

If you are doing this test to an O-320H or O-360E for some reason, be advised that the oil volume pumped out of the engine in this test will be about a quart per cylinder, and possibly a little more. Be sure you have enough oil in the sump to start with. In contrast, there will be very little oil in the collection cans if you are testing any other model of Lycoming engine. Exception -- we have not done this test on a Beech Duke so you are on your own with one of those.

2. In addition to the above hardware, you will need screwdrivers (or speed wrench/electric drill attachment) for removing cowl screws, lacquer thinner and clean rags.

3. Fly the aircraft long enough to achieve normal cruise oil temperature on the cockpit gauge (approximately 180F). Land and taxi immediately to the test location.

4. Work as rapidly as possible since you do not want the oil to cool any more than necessary. Remove sufficient screws to gain access to the inside lower cowling adjacent to and below each of the cylinders. You need enough working room to disconnect the oil return tubes and to duct tape the cans to the lower cowl sides. This may be simple or difficult depending upon the airframe you have.

5. Use clean rags and lacquer thinner to clean the inner surface of the lower cowling sides so that duct tape will stick to them.

6. With duct tape, attach cans 2 and 4 (possibly 6) to the inside left lower cowling and cans 1 and 3 (possibly 5) to the inside right lower cowling (cans 1 and 2 forward). Use two or more straps across each can, since the tape will melt some during the test and you absolutely do not want the cans to drop away and spill oil.

7. With a wrench, unfasten the oil return tubes from all four (or six) cylinders and move the tubes out of the way. Install the two inch long stub tubes in their place and route a flexible hose segment from each stub tube to the corresponding can. (Or use hose segments without the stub tubes, as mentioned in paragraph 1 above.) Cylinders 1 and 3 (5) are on the copilot side of the engine with 1 at the front. Cylinders 2 and 4 (6) are on the pilot side with 2 at the front.

8. Close the lower cowl sides, making sure the hoses and cans are not in direct contact with any exhaust component. Secure both lower cowl sides with a few machine screws as appropriate for a ground run.

9. Close and secure the top cowl if it has been removed.

10. Establish an aircraft monitor with a fire extinguisher to watch the cowl area during the test. In the event the monitor sees any smoke or leaking oil, the test must be stopped immediately and the aircraft attended to.

11. Set a stopwatch or timer to zero and start the engine. Immediately establish 1000 RPM and start the timer. Leaning is at your discretion. Use the following test sequence:

12. At the end of the above 12 minute test sequence, pull the hoses off of the stub tubes and use shop rags to catch any further oil drips.

13. When the engine is sufficiently cool for working inside the cowling, remove the four (or six) cans, cap them and set them aside.

14. Remove all duct tape and any melted remnants of it. Remove the stub tubes from each cylinder and reattach the oil return lines. Clean up any spilled oil, assure the engine is in an airworthy condition and reattach the cowl assembly with the removed screws.

15. Pour the oil from each can into separate wide-mouth containers such as a short drinking glass. Be sure to label these containers 1 to 4 (or 6), consistent with the can numbers.

16. Using a calibrated syringe, or some other measuring device, measure the total number of cubic centimeters in each container.

17. Now you can see where you stand. Our testing has shown that cylinders with less than 50 cc of collected oil during this test are inclined to premature valve failure. 100 or more is preferable. The lowest amount collected to date has been 13 (from a valve failure cylinder) and the highest 280 (from a high time engine with no valve problems). In almost every case, cylinders 1 and 3 (5) receive less oil than do 2 and 4 (6), for reasons explained in "The Rest of the Story" on this web site. Not surprisingly, most of our cylinder problems are with 1 and 3 (5). You can get some feel for the health of your engine's cylinders by comparing their oil flows to this information.