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Oil leaking at cylinder base nuts- help

lndwarrior

Well Known Member
Engine is a Lycoming O-235, recently overhauled. The two bottom cylinder base nuts appear to be leaking a small amount of oil that accumulates to a drop or two as it runs down the case (after a short flight). Engine has about 10 hours since over haul.

How concerned should I be? Suggestions or recommendations?
Tia
Gary
 
Leak

Most likely cause: improperly installed cylinder base o ring or damaged contact surface for the o ring. Most common cause for this is allowing a connecting rod to hit the chamfer where the o ring makes contact.
I don't know if any of the 0 235 engines have thru studs. If there are thru studs the o rings around the studs at the center of the crankcase are another possibility.
 
Are you sure that's where your leak is? Oil leaks are tough to isolate as airflow in the cowl can move oil into all sorts of places, hiding the true source.

I had an annoying leak for a year and finally traced it to loose oil return hose clamps next to the case during my recent conditional. Just an option before you tear down a fresh rebuild. Woody.

Engine is a Lycoming O-235, recently overhauled. The two bottom cylinder base nuts appear to be leaking a small amount of oil that accumulates to a drop or two as it runs down the case (after a short flight). Engine has about 10 hours since over haul.

How concerned should I be? Suggestions or recommendations?
Tia
Gary
 
Are you sure that's where your leak is? Oil leaks are tough to isolate as airflow in the cowl can move oil into all sorts of places, hiding the true source.

I had an annoying leak for a year and finally traced it to loose oil return hose clamps next to the case during my recent conditional. Just an option before you tear down a fresh rebuild. Woody.

It sure looks like it. But I did have an oil return hose leak as well.
 
Leak

I had the same issue. I'm guessing the oring on the through bolt got pinched during the overhaul. I removed the bolt and put some thread sealer on the stud then re TQ the bolt. She sealed right up.
 
The two small nuts? Or the bigger corner ones? Step one is check torque on all 8 nuts. If only a couple are untorqued, somebody messed up their torque sequence. If all/most are loose, you got a problem. If you're sure the leak is at the small bottom ones your case may have gotten a rod whack, as somebody said. Might not even have a base seal (oops).
 
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