Oil Leak Crank Case Half Bolts

[dcastor]

On a recent flight I found a small amount of oil on the back side of my prop and a smudge on the engine cowling (see photos).  I was afraid it was coming from the prop hub, but after removing the engine cowl we found more oil on the engine.  After cleaning the engine well and an engine run, it seems to be coming from 3 bolts along the top of the case that hold the halves together.  Mechanic checked the bolts and they seemed tight, though he didn't use a torque wrench.  He wants to run fix action by the head mechanic, but he's leaning toward removing the bolts and applying thread sealant to stop the leak.  Sorry I didn't get a photo after cleaning and engine run.

Sound reasonable?

Dave C

[MB65E]

That is a LOT of oil. Feel free to run a bead of proseal along the top of the case, but with that amount of oil I think it's much more than just the case halves seaping. I would inspect the case for cracks. Also, the front crank seal is a known leaking point. 

Above the part in the case that says #2 looks suspect, but I've never seen a Lycoming crack there. 

-Matt

[rgpilot]

I had three come loose on my old J. The mechanic just tighten them and they stayed leak free for about 2 years. I just retightend them and never had another problem.

[Piloto]

Looks to me like that the leak may be coming from the crankshaft seal. Leaks from the bolts stay around the bolts since there is no pressure. But pressure leaks like from the crankshaft seal spray out over a large area. You can see a crankshaft seal leak by setting the engine to 2,000 rpm and then pulling on the prop control to about 1500 rpm to force oil pressure into the seal. You may notice also small droplets on the windshield. Seal leaks are sometimes momentary due to a small particle in the seal that get dislodge later on. Cut open the oil filter to check for particles.

José

Edited January 16, 2017 by Piloto

[markejackson02]

That is a lot of oil.  I had two of them leak after the engine was overhauled and they were re-tightened to the specified torque values, no problems since.

That looks like it may be something other than the bolt.

 

[Guest]

Leaking front seals, leaking case bolts, leaking thru studs and cracked cases are fairly common Lycoming issues.  Start with thorough cleaning and ground run to determine the source.

Clarence

[Shadrach]

That does not necessarily look like a lot of oil to me.  I have seen what a lot of oil does to an engine compartment and your's does not look so bad. Just a few ounces of oil can create an unbelievable mess.  Like others have said I would suspect the crank seal first.  Clean and dry the engine, and then try a few brief engine runs with the cowl off and reinspect.  I have used foot powder in the past to look for leak, but I think it is more trouble than it is worth.  

Our case cracked at one of the bottom bolt bosses and just started to propagate toward Cylinder #1.  It was puking so much oil that is literally smoked at taxi speed. At shut down I thought I had a fire. 

[thinwing]

I agree....from pics I cannot determine Source of leak lycoming cases are sealed by a single silk thread....a case bolt can start leaking after case bolts were loosened to attach a bracket..very common...than its remove the case bolt and totally clean surfaces of oil and than pro seal the bolt hole and bolt and washers...usually stops leaks...The other question..if case gets pressurized by excessive blowby from cylinders due to a cylinder/ ring failure...??

[dcastor]

17 hours ago, MB65E said:

That is a LOT of oil. Feel free to run a bead of proseal along the top of the case, but with that amount of oil I think it's much more than just the case halves seaping. I would inspect the case for cracks. Also, the front crank seal is a known leaking point. 

Above the part in the case that says #2 looks suspect, but I've never seen a Lycoming crack there. 

-Matt

Matt,

I'm not sure that proseal on the top of the case would help, the oil did seem to be coming out of the bolt holes themselves, not between the halves.

The mechanic checked the crank seal pretty thoroughly, after cleaning the engine with mineral spirits.  No leaks found in that area.  In fact both mechanics at the shop did a pretty thorough look over the case and didn't find any cracks.

I think you are noticing the pooling of oil above #2...it was dry after cleaning and the engine run.  I think in the photo posted the oil was just pooling there because it's a flat spot.

Dave

[clh]

I chased leaking bolts for about 5 years before I just decided the engine was 30 years old, at TBO, and needed a reseal.

I had some success with sealing the top bolts using the remove, clean surface, apply sealant, replace bolts and re-torque.  I never had much success with the bottom bolts.  They leaked until I replaced the engine.  No more leaks, but quite a pricey fix.

As to quantity,  +1 on the "a little oil goes a loooong ways".  I had oil dripping onto the nosewheel all the time, but no noticeable increase in usage.  (maybe 1/2 qt between changes).

 

[copierdynamics]

I believe Lyc makes oversize bolts for this problem.

[thinwing]

5 hours ago, copierdynamics said:

I believe Lyc makes oversize bolts for this problem.

Nope .They don't...

[jclemens]

Oversized thru-studs, yes. There are also a number of case mods that involve dowel pins and O-rings aimed at stopping thru-stud oil leaks.  We have them incorporated into every Lycoming engine we build.