AESpecialists

Corrosion initiated cam failure is by far the most common occurrence. While it's possible a cam could just wear out, we've seen cams make almost 9000 hours in service with two regrinds and still be servicable (although the third grind would be pushing it) Cam failure and spalling lifters may not be immediately recognizable in the oil or filter. The flakes of metal are flung into the cylinder bores and become embedded in the piston skirt which keeps them out of circulation. One of the issues with flat tappets (and true of old cars as well) is that the EPA mandated the removal of phosphorus based additives from base oil stocks. These were the additives that helped with 'wiping' friction such as cam on tappet. With roller lifters such as in most automobiles or overhead cams, this isn't an issue. Lycoming sells a phosphorus additive that addresses this lack, as do some of the proprietary oils and additives on the market.

As others have pointed out, once the hardened surface of the cam is breached, wear is very rapid. Once that threshold is reached the cam can go in as little as 5hrs of operation, so the last oil change being fine is not really relevant. I'm willing to bet the piston skirts have little bits of steel embedded in them, which is typical, and a diagnostic tool of cam failure vs cylinder issues. Even if the decision is made to repair and move on, they will need to be replaced. SB240v outlines mandatory replacement items at overhaul if you want to compare to the logbook entry or 8130.

Lycoming offers several different springs for the OP adjuster. If you at max adjustment (in) and still not getting the right pressure you can swap to the next spring to get the range of adjustment back

Even the oldest manuals will advise you check for revisions and use the latest data provided. Otherwise just what is the mechanic signing off? "IAW what I felt like today"

Not true, although you're right, some old-timers will argue that. Latest revision of Lycoming's overhaul manual explicitly states that all SB's and SL's are to be considered PART OF THE MANUAL. There is a very clear list of inspection criteria in SB533B that states a complete teardown is necessary. One other point. If the owner said he "scoped" the cam and lifters, implying that it was done with a borescope instead of taking off a cylinder and looking inside, then he is being less than truthful. There is no way to get a borescope there. I really wish there were it would have saved time and $$ in the past

Think of the engine as a runout core at the cheap end of the spectrum. Lycoming (and Continental) both have 12 year calendar TBO's for a reason. In 42 years there is an entire binder full of AD's and SB's that most likely have not been complied with. All of the seals and gaskets are well beyond their 'sell by' dates, and while it may not yet, as soon as you start putting some time on it, I'll wager it will leak oil like a sieve. The estimate of $10K in additional parts may not be too far off, sadly. Between AD required repairs, and corrosion that might be a conservative estimate

You should keep separate log books (or at least separate and separable sections in the master log) for the airframe, the engine, the propeller and any other major component that has a life independent of the airplane as a whole. Either through damage, wear or just quirk of fate, you can replace the propeller and engine separately, and each needs it's own documentation. The removed engine will take a huge hit in value, 50% or more- even as a core- with no log book. Ditto prop. Trippo if any of those components has a hard life-limit or inspection tied to time in service.

The best answer is 'it depends' As an assembly there isn't a set limit to how many times an engine can be overhauled. Certain components will have a limit to the number of times they can be machined, for ex. a Lycoming crank can be ground .003, .006 and .010 undersized, but after ten thou it's no longer repairable. But, it may not need grinding every overhaul, or it may need the max grind the first time around due to corrosion or damage. The crankcase has a minimum deck height ('thickness' from center line to cylinder base), but between production tolerances and the amount of material that has to be removed from the mating surface to correct any problems that could be anywhere from one time (unlikely) to five times(equally unlikely, but possible). Cylinders have a finite, but variable life as well depending on a lot of operational factors, and possibly the phase of the moon. Most other components, like gears and such are solely on condition. Putting my salesman hat on for sec, only the factory can 'zero time' an engine, but in reality that's just an overhaul with no history and a fancy new logbook. They use servicable used cranks, cases, rods etc just like any other shop might

Simultaneous failure of things with similar symptoms is frustrating at best. Just as bad as an intermittent electrical problem. Congrats of finding the problem(s)

Like has been said, no intent of fear-mongering. Our experience as an engine shop is a little different than the average mechanic, because, other than simple TBO overhauls, we see many more major or catastrophic failures. If it's an easy fix, or a simple thing, it doesn't make it's way to us. I suppose it's like a surgeon vs. a family doctor. We don't treat the sniffles<G>

By knowing what bits are made of what metals, oil analysis, or rather a sudden change in the results, can hint at what may have failed. A spike in lead / tin indicates failure of a main or rod big end bearing pretty conclusively, since there's nothing else with those elements. A spike in copper /and or brass is likely to be a rocker arm bushing. It could also be a rod small end, piston pin plug (possible bent or twisted rod) or, on Continentals, the starter adapter or accessory drive shafts as well. On Lycomings a spike in iron/steel is most likely a cam failure in the works, but never a good sign at all. Lycoming cam failures will telegraph themselves with steel specks imbedded in the piston skirts, so if you have a cylinder off for any reason look there.

My card reads Engine and Parts Sales, but I am also NDT tech, coordinate with the inspection staff, deal with vendors and tech reps, liase with the FAA, make coffee and, on a bad day, do facilities maintenance. I've been with this shop in various capacities for over seven years. My personal background is in antique aircraft, sporst car racing, and industrial archaeology. Mark

You are correct on the chemistry, sir. I was mixing up nitriding and carburizing in my head as I was typing. The net result is still a case hardened surface with a skin of hard material over a more ductile base.

Bendix and Slick both recommend 500hr inspections. Should be roughly $350 each on average. Cheap insurance, along with checking/replacing the harness and plugs. The Dual Bendix mag is more expensive proposition. Bendix is part of Continental and they saw no interest in supporting a magneto only used by Lycoming. They stopped making OEM parts about two years ago, and the PMA parts have only been trickling in. Converting to seperate mags is an expensive task, provided it can even be done legally. Check the type certificate data sheet. Some a/c were certified with both single and dual mag variations, soe were not.

Lycoming (and Continental for that matter) set a calender TBO of twelve years for a reason beyond the simple desire to sell parts. There is the corrosion issue already mentioned. There is degradation of rubberparts like oil seals, pushrod tube seals, mag drive cushions, etc., and perhaps most important is the backlog of AD's and SB's that may never have been complied with. Never assume that they have been done. We had an engine come through once that had a 61 year old outstanding AD on the camshaft.