I have 150 hours on chrome cylinders in an IO360-A2B. I have high oil consumption (two hours per quart). What is going on? Should I worry? What can I do about it?
Editor:
This is a commonplace scenario. I always advise people against chrome cylinders. They are good from a wear standpoint, but they are very difficult to break in properly (and seldom are). There are several other good alternatives now, and it just isn’t worth taking the chance on the chrome plating approach any more.
Before I opine on the cylinder status, I need to caution you that you should get a current compression reading on each cylinder, taken right after a short flight and landing. The cylinders should still be hot when the reading is taken. There are possibilities such as broken rings, that I am not including in the following observations. I am assuming that nothing is mechanically wrong, but you need to conclusively rule that out. If you suddenly went from seven hours per quart down to two, the odds are dramatically higher that something is mechanically wrong. In most cases of things like broken rings, a borescope exam of the cylinders will confirm or refute the diagnosis.
There are three key possibilities for continuing high oil consumption on chrome cylinders:
– The chrome surface was not properly ‘channeled’ when it was plated. The channeling creates fissures in the chrome that hold oil, and they make it possible for the rings to properly seat during break-in.
– The wrong piston rings were used. Chrome cylinders require iron rings, while steel cylinders require chromed rings. If chromed rings are installed in chromed cylinders, the rings will never seat properly, and the cylinder cannot be ‘broken-in’. This mistake is seldom made by an experienced cylinder or engine shop, but is commonly made when an FBO technician takes on the job himself. This occurs because the standard cylinders are steel, and the standard rings are chrome. The chrome rings are the ones most commonly found and used. Your shop should have given you a copy of the work order showing you the part number of every new piece that went into the engine. You ought to be able to determine the ring type used, from the invoice.
– The engine was not operated aggressively enough during break-in. Temperatures permitting, the new chrome cylinders require operating the engine at full power, or virtually full power (red-line permitting), for the first 20-30 hours. This obviously means using rich mixtures, as well as fast, well-planned, power-on descents. It can take as long as 50 hours for chrome cylinders to break in; sometimes even more. If this is not done, the channels in the chrome accumulate varnish (cooked/coked or burned-on oil). The varnish becomes a hard brown-to-black glaze, and no further break-in can occur beyond that point. Once this occurs, the only remedy is to remove the cylinder, pull the pistons, hone the cylinders to remove the glaze, and try again.
If you satisfy yourself that there are no mechanical issues related to the sudden spike in oil consumption, you can try operating only at high power settings for the next 50-100 hours, and see what happens. The two hours per quart is still within the Lycoming spec for this engine; and this engine likes to use oil anyway (which is not a bad thing in an aircraft engine, within reason). If you are getting oil fouling on your bottom four spark plugs, you can replace the bottom ones with fine-wire plugs to solve that problem. I recommend doing this anyway, as the fine-wires need far less servicing, and will usually last to TBO.
The consumption rate is not yet exceeding the max usage algorithm (search BAC for oil consumption). It is almost certainly being burned, not blown out. You can try maintaining the sump at 6 quarts rather than 8, if you aren’t already. Without a separator, there is a tendency to ‘blow out’ the top two quarts. You can also make sure you have the correct dipstick, by checking the oil level immediately following the next oil change. With an oil filter change and 8 quarts of oil added, followed by a brief run-up and leak check, the correct stick will read about 7.5 quarts. Closer to 8 if you have no oil filter.
I like the separators. The M20 is the only one worth installing, for a number of reasons. It has to be mounted just like the directions say; as high as possible, with the feed hose running up-hill all the way; and with the drain-back tube Y-d into a rocker-box tube (not T’d in). The vent pipe (or newly-fabricated vent pipe) should not extend beyond the edge of the belly, and should have a square cut on the bottom (not angled aft). If it extends below the cowl, or has an angled cut on the back, the relative airstream will create suction that pulls vapor out of the engine. You don’t want that with the separator installed. It is unlikely that the separator will reduce your oil consumption, unless it is due to being kept above six quarts in the sump. The M20 will enable you to operate with eight quarts, without blowing any out, It won’t reduce any that is actually being burned, but it will let you keep the sump full, so you can operate up to three-hour flights (assuming two hours per quart). The engine only needs two quarts in the sump, to prevent damage, as long as the oil isn’t running hot.