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Oil Pan Seam Leak

J

jahoosafat

Active Member
Hi All - My RV-10 with a Lycoming IO-540 has been a dependable steed for a number of years, acing most of her condition inspections with only minor squawks. I recently noticed a small oil puddle that would form behind the nose wheel fairing after flights. I do my own oil changes, but I definitely need an A&P to look at and fix this. The diagnosis was that the leak was coming from a seam of the oil pan. See this pic: https://photos.app.goo.gl/Mm36FV1QEECAkD1XA . The recommendation is to tighten the through bolts and apply epoxy. My understanding is that epoxy was applied to this location previously and presumably wore out (or the seam gap is getting larger). The alternative fix is to remove the engine, put it on the bench, and do a more permanent fix. Have folks seen this issue before with Lycomings? Does this sound like a good course of action? This is a new maintenance shop that I'm using, so I was interested in the perspectives of Vans builders. Thanks for any information you can provide.
 
jahoosafat said:
Hi All - My RV-10 with a Lycoming IO-540 has been a dependable steed for a number of years, acing most of her condition inspections with only minor squawks. I recently noticed a small oil puddle that would form behind the nose wheel fairing after flights. I do my own oil changes, but I definitely need an A&P to look at and fix this. The diagnosis was that the leak was coming from a seam of the oil pan. See this pic: https://photos.app.goo.gl/Mm36FV1QEECAkD1XA . The recommendation is to tighten the through bolts and apply epoxy. My understanding is that epoxy was applied to this location previously and presumably wore out (or the seam gap is getting larger). The alternative fix is to remove the engine, put it on the bench, and do a more permanent fix. Have folks seen this issue before with Lycomings? Does this sound like a good course of action? This is a new maintenance shop that I'm using, so I was interested in the perspectives of Vans builders. Thanks for any information you can provide.
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Need a pic with a wider view, but IMHO it is coming from the area near the stud/nut and not the crankcase seam. You can see the oil travelling down from that area and then clinging to the crankcase seam area and moving forward along the seam. Oil rarely travels upward, so unlikely flowing from the seam and then UP to that area. I would be looking for a source such as the lower cyl hold down bolt directly above that area. The oil spot is several inches from the oil pan, so have no idea what the A&P was thinking
 
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Interesting theory. I'll try to get a wider angle pic of that area. The A&P used a die to find that the leak was coming straight from the seam. He also tightened every bolt to the Lycoming torque specs. Then applied the epoxy.
 
Jeff, if you would, give us an update next time you pull the cowl. I'm interested to hear if that resolves your issue.

jahoosafat said:
Interesting theory. I'll try to get a wider angle pic of that area. The A&P used a die to find that the leak was coming straight from the seam. He also tightened every bolt to the Lycoming torque specs. Then applied the epoxy.
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Lycoming

The approved sealants for crankcase mating surfaces are Hylomar with silk thread or RTV without thread. Fuel tank sealant would be a better choice than some generic epoxy if the leak is at the case split. That leak appears to be well below the cylinder flanges.
 
Absolutely I'll update again if the leak presents again, and I'll definitely circulate pics of the area when it goes in for the condition inspection in October. In the meantime, if anyone else has seen this issue and worked a solution, please feel free to add your experience(s).
 
jrs14855 said:
The approved sealants for crankcase mating surfaces are Hylomar with silk thread or RTV without thread. Fuel tank sealant would be a better choice than some generic epoxy if the leak is at the case split. That leak appears to be well below the cylinder flanges.
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Thanks for this info. Does this info come from Lycoming?
 
Lycoming info

The sealants for crankcase split are long established procedures. Service bulletins should address that. i have only used Hylomar with excellent results. Hylomar is non hardening. There are other generic names for hylomar. I don't believe the external tank sealant is an approved procedure. I saw that used 20 years ago, seemed to work.
 
Crankcase

Lycoming Service Instruction 1125D calls for POB #4. Spruce does not list this. They do have Hylomar. 1125D now lists a locktite alternative as well azsz the RTV spec.
 
This probably does not apply, but:
Many years ago, partner in a 182 (TCM engine) came back from a flight into the freezing levels with oil all over the inside of the engine cowling. After looking at the engine for what seemed like forever, we realized that after a previous overhaul (supposedly reputable shop) the oil pan had been re-installed with every bolt on the right side safety wired backwards! Sure enough, they were all now a half turn loose. Compounding the problem, the crankcase breather was full of gunk and, we surmised, at below freezing temperatures had slightly pressurized the crankcase. Cleaning the breather, torquing the screws and te-safety wiring correctly fixed the problem.
 
Just this morning, I stopped seam leakage by using the method that a well know overhaul shop uses- even on the fresh o/H that may seep. They use loctite 290 - it is a thin wicking liquid. Apply a hair at the leak source and a vacuum at the case breather to suck the loctite 290 into the seam. Wait about 10 min and runup again after cleaning area real good. With a blacklight, oil will show up (so will the loctite) without a dye. To keep your sanity, cleaning the area is essential on subsequent applications. (I painted over the seam, as I had too many attempts and couldn't get it quite clean enough that the blacklight would highlight the oil and the loctite)

From the engine shop...most or all lycoming will leak at the seam at some point in their life.. That said, I agree with whoever suggested that it might not be from the seam...I would like to see higher up.

Of course, the weep or leak does not affect serviceability, rags work good to clean with :) until it gets to your personal ocd level! haha
 
I suppose there's no way of knowing without taking the engine out and opening the case, which we're not going to do at this stage until I see further signs of the leak continuing.
 
Not trying to override a factory recommendation, but leaking on a case seam would be caused by shearing of the joint damaging the build silk seal. While the external application of "sealant" can treat the symptom, a little further investigation might be in order to ensure the case is not shearing. That would be to verify that the main case through bolts are not loose.

I would not be happy unless that was checked (with a torque wrench) and acceptable. All the through studs at and forward of the front main bearing.

Not knowing how many hours are on the engine, it could be getting close to TBO, or be on its second overhaul. Either way, if the shearing of the cases continues, one could expect case work being required for the next overhaul. While not an airworthiness issue, it could be a consideration for the longer term. An owner decision.

A most satisfying outcome would be a finding little oil trickling down from the front main seal, indicating it is not a case leak after all.

2 cents.
 
Case sealants

Lycoming allows three different sealants for case split. Only one of the three uses silk thread.
Reuse of lock washers on Lycoming's is relatively common. The washers are one torque cycle only, then throw them away.
 
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