Leaky Lycoming

[Htaylor]

I've been instructing in a Cherokee 140 with an engine that has begun leaking oil at the case seal around the case bolts. Top near the front. I've seen other aircraft engines that have been gooped up with something like silicone/JB Weld to stop this sort of oil seepage. Is this an accepted repair technique, a real hack job that simply should not be attempted, or something in between? Even if it's an accepted repair, is it just a band-air for case halves that are fretting and wearing against each other?

This O-320 has 1500ish hrs SMOH. Not sure of the calendar time, but I suspect it's beyond 12 years. It's not my plane, so I won't be making any repair decisions. But I do fly it quite a bit with a few student pilots and would prefer they not learn its OK to fly unsafe, illegal or otherwise un-airworthy aircraft. Thanks in advance.

 

[SixPapaCharlie]

Probably a hack job.

Mine leaks. That's how I know its working.

 

[Stewartb]

The silk thread is inboard of the bolts. If the bolts leak, the seam should seep as well.

 

[Dan Thomas]

Old engine, old, dried-out sealant. Tightening the case bolts might do more damage than good, by damaging the aluminum case. The torque spec on those bolts is really critical. From the Lycoming manual:



About the only external repair that I've seen work at all is to clean off the seam real good and apply a bead of PRC to it. Oil will often just lift silicone sealants off the metal. Silicone can be dangerous in the wrong hands, too. The temptation is to start using it on everything.

 

[Pinecone]

There is a method using a vacuum and Loctite 290.

It was presented at a Lycoming seminar. A person on BT used it on his engine and it worked well.

 

[Htaylor]

The silk thread is inboard of the bolts. If the bolts leak, the seam should seep as well.

The seam does leak. As a former motorcycle mechanic, my concern about re-torquing is deforming the case slightly even though these cases are far beefier than a motorcycle case. As and aside, how much is too much? Oil can be seen running down to the cylinders.

 

[sourdough44]

Yes, how much is to much, that’s the issue. With to much, could end up with a fire. If it’s just minor, no biggie.

If unsure, I’d run it by a local mechanic.

 

[Lon Stratton]

Did the Loctite process, but no luck. Finally did the PRC and that worked for the last several years. Installing a Factory Rebuilt right now and I hope to get 4-5 years of no leaking, but we'll see.

 

[Stewartb]

The first thing I’d check would be what type of oil they use. Aeroshell 15/50 will leak out of places where other oils won’t. Maybe an oil change is all it needs.

 

[Dan Thomas]

Did the Loctite process, but no luck.

That would be typical. Loctite needs really clean surfaces, and how do you get the oil and varnish out of those mating faces? You can't. Loctite also needs ferrous metal present to catalyze it, or the use of a Loctite primer, or it won't harden properly. So it might set up around the bolts but that's about it.

If the Loctite process isn't approved via engine manufacturer's documents, I wouldn't trust it. Some Lycoming guy's suggestion at a seminar does not constitute an FAA-approved method.

I used many types of Loctite over many years, in machine shop work, in rebuilding and remanufacturing, and in aviation maintenance. And there are many, many types. There are suitable places for them, and there are places where they have no business being at all. It can get into the case and harden and break off and mess up the oil pump, for instance.

 

[SebIp]

We had a sudden on set of leaking. It coincided with cracking of a shroud, twice. That turned out to be dry tappet clearance. Whenever the last set of jugs were done the rod lengths weren’t correct.

Once we reduced the vibration the leaking reduced. It still leaks but now it just seeps a bit.

The real question as others have said is whether the issue is serious or just acceptable seeping. Sometimes leaks are from cracks so it’s important for it to be checked leaks are not that.

 

[Lndwarrior]

I have been chasing leaks on my O-235 for 6 years. No doubt I've fixed a bunch - oil return lines rocker covers gaskets, prop seal, oil filler, intake tube connectors, and probably a few more I can't remember. It still leaks as much as it ever did... As soon as you get one thing fixed, something else starts leaking. Now it seems it's the case bolts. I've resigned myself to just cleaning up the mess every half dozen flights.

 

[Dan Thomas]

I bought numerous Lycoming factory overhauled engines. The only leaks I had to deal with were the rocker cover gaskets and the oil return line connecting hoses. The gaskets were cork, and the heat ages them quickly. It got so I took those covers off as soon as we were installing the new engine and put the red silicone gaskets in. The hose clamps on the return tubes needed periodic retorquing, and if we owned the engine long enough, new hoses were installed.

I have seen more leaks on field-overhauled engines. In one, the tach seal was leaking. In some engines, that means the whole accessory case has to come off. The installer had used no sealant on the OD of the seal, and the shaft was scored by the old seal. Lycoming doesn't fool with marginal stuff like that, and they do enough engines that they tend to get things right.