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Case Seam Oil Leak

M

mic2377

I'm New Here
Hi All,
This is quite a start as my first post on VAF... I had recently purchased a RV-7A. It was noted to have consumed some oil (1 quart/6-7 hours) by its previous owner. It has an Aerosport Power O-360 A1A, and the aircraft/engine is fairly high-time, having 1055 hours in total. The engine had been IRAN'ed early in its lifespan due to a stall/spin accident which had resulted in a propstrike, followed by cylinder removal at ~825 hours due to rough running (which turned out was actually due to a bad Lightspeed coil pack). The cylinder work was done locally by a mechanic who is no longer working.

On pre-purchase inspection the oil was relatively clean after 20 hours, the plugs were not oily, and the filter was also looked good. I assumed that this oil consumption was reasonable and had flown it ~30 hours since purchase.

Unfortunately the oil consumption had continued to increase, and had reached a quart every 3-4 hours. I had also found significant oil on the belly of the aircraft, but no leak at rest. I evaluated this with the help of my local A/P as the aircraft was due for condition inspection at that time anyways.

We ultimately determined that there was significant oil leak from front case seam, with considerable oil on the top of the airbox. It was also found that the at least one of the cylinder case studs, and one of the thru-bolts, was loose as well.

My mechanic reports that he has seen some Lycomings suffer case leaks, and still be airworthy, although we both agreed that rectifying this would require a case split/reseal. He retorqued the loose studs in question.

I am admittedly rather uncomfortable though about continuing to fly the aircraft in the setting of the loose thru-bolt/case studs, and have grounded it. My current plan is to get it professionally IRAN'ed with case resealing at this time. Is this over-reaction on my part? An oil leak is one thing, but the loose studs after cylinder work make me much more worried about a potential bottom end issue.

The engine work will be done at Penn-Yan mainly due to proximity.
 
A case leak can be fixed with Hylomar sealant, without splitting the case.
https://hylomar.com/hylomar-m/
Loose thru-bolt/case studs is a different story.
If the bolt was very loose and the crankshaft bearings have moved from their
normal position, the engine needs IRAN work.
On the other hand, if the bolt was just out of torque specification, no harm was
probably done to the bearings.
If the bearings have moved from their normal position, there will be evidence
of that in the oil filter. You need to discuss this with someone who is qualified.

Good luck
 
I was successful using locktite 290 and a vacuum cleaner to suck it into the seam. Use the vacuum at the breather. The 290 will weep into the seam. A black light to check for oil along the seam before and after is helpful. A through cleaning before and after is also important, as the oil gets blown everywhere in the cowl and it can be difficult to fin the origin of where the seam is leaking.
 
On the seam leak, I suspect that it may be possible with various methods to seal most or all of it and would try that before a tear down. I had a leak on one of the fixed barrel studs (not a through bolt) and fixed it with the green wicking loctite. It can also be removed, cleaned and re-sealed without splitting the case. On the through stud, was the nut loose or was the actual through stud loose. This is a light interference fit stud and if it can be slid back and forth inside the case, that is going to need to be addressed and that means the case going to a shop or with a skilled mechanic, you can likely ream it and install the over size stud in the field, if it is a wide deck. These will leak oil once loose and any means other than a bore / ream and new stud should NOT be attempted. If you have confirmed oil coming out of the area around the nut of the through stud, that means the fit is compromised.

Larry
 
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If the nut on a thru-bolt was not torqued down properly you may consider replacing that thru-bolt or having it inspected (MPI)...they could suffer damage without proper torque. There's recent posts about cylinder studs breaking from this.

If there was a leak from the threads of the thru-bolt, you may have fretting on that main or oil made it's way through the main because it wasn't properly torqued. You can do SI 1290 to stop the leak but eventually the case may need repair. I successfully performed SI 1290 with a P005 through bolt. I thought I had a seam leak and it turned out to be a thru-bolt leak. Airflow in the cowling makes a oil go everywhere and collect in unusual places

Depending on the engine model, or journal where the thru-bolt that was loose, the bearings are probably doweled and there's tangs on the bearing...you usually don't need to worry about spinning a bearing from loss of torque.
 
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I had mine leak through a through bolt due to case fretting nicking the case seam o ring. If the through bolts were loose and the engine was operated it’s very likely the case seam is leaking due to fretting. An IRAN will reveal this and if the dimensioning of parts looks good then yes you could just slap it all back together. I’d recommend sending the case to DIVCO for a real inspection, they can install dowl pins IAW with the lycoming mod, you will never have case fretting issues again. The dowls make it so tight I almost broke my case splitting tool to get it apart after dimensioning.
 
I want to say thank you to everyone's input. I will be removing the engine this week to take to Penn Yan to be IRAN'ed. It is my understanding that they use Divco for most of their case work. I don't have the specialty tools to do this work myself.

I would have considered the vacuum/sealant trick if a) there weren't any loose case/cylinder studs, b) I didn't fly the aircraft at night and/or over the Great Lakes, and c) the oil leakage hadn't continued to worsen. I'll sleep better at night having addressed this definitively.
 
Majorpayne317641 said:
The dowls make it so tight I almost broke my case splitting tool to get it apart after dimensioning.
Click to expand...

You're not kidding! I just did this. I was so afraid of damaging the case that I ended up sticking it in the oven an heating it up to 250F to loosen up the interference fit a bit (Aluminum case grows larger than the steel dowels)
 
A quick update - I finished removing the engine and dropped it off at Penn Yan. The removal process was quite an adventure (I am not the original builder!), and was made significantly worse by the fact that everything on the underside of the engine was absolutely COVERED in oil.

When stripping everything down, I found the lower coiling and nose gear fairing to be absolutely filled to the point of dripping oil. This is after having been cleaned up during the condition inspection ~5 hours of ago. Interestingly enough, the plane only leaked very minimally at rest, I think it only leaked significantly when the oil was hot and thinned out. I also found a bunch of burned-on oil on the outside of the exhaust pipes.

I will say that I have a much better understanding of the systems of the aircraft after tearing it down. It took about 15 man hours, with a little bit of assistance from a friend to remove the prop.

I also got a tour of Penn Yan when I dropped the engine off. I was very impressed by their shop. The number of specialized machining/measuring tools and fixtures alone is staggering. There is no way a home mechanic could come to the quality of IRAN/overhaul they do.
 
Penn Yan

Penn Yan is the best engine shop in the business. Bill Middlebrook and his crew will give you back an engine in which you can have full confidence. I fly two of their engines.
 
A quick update on the progress from Penn Yan - it turns out it was good that I sent the engine in for rework. The case had significant fretting damage, which was likely responsible for the case seam leak. The cam/lifters were bad as well, and the crank needed some journal rework too.

Fortunately the case and crank issues could be corrected with reconditioning, and nothing ended up getting red-tagged. The engine is also getting a roller cam/lifters. Unfortunately these are VERY expensive and really added alot of $$$ to the bill, but my hope is that they are superior technology and will significantly reduce the risk for cam/lifter problems in the future. The cylinders were within spec as expected.

It looks like it will be done in November, which in the post-pandemic world is quite a good turnaround time.
 
mic2377 said:
A quick update on the progress from Penn Yan - it turns out it was good that I sent the engine in for rework. The case had significant fretting damage, which was likely responsible for the case seam leak. The cam/lifters were bad as well, and the crank needed some journal rework too.

Fortunately the case and crank issues could be corrected with reconditioning, and nothing ended up getting red-tagged. The engine is also getting a roller cam/lifters. Unfortunately these are VERY expensive and really added alot of $$$ to the bill, but my hope is that they are superior technology and will significantly reduce the risk for cam/lifter problems in the future. The cylinders were within spec as expected.

It looks like it will be done in November, which in the post-pandemic world is quite a good turnaround time.
Click to expand...

Thanks for the feedback. Were the Penn Yan Aero guys able to determine the root cause of this leak? Perhaps we can get some hints about how to avoid this.
 
I suspect the root cause of the leak was that the engine had cylinder work in 2018 when all of the cylinders were for "running poorly". It turned out at that time that cylinders had been in perfectly fine shape but the Lightspeed ignition had a bad coil pack. I suspect what happened was the engine was turned over without torque plates installed, and the thru-bolts and cylinder studs were incorrectly retorqued. As a result the case seal failed and the case was subject to fretting.

The sad thing about this is that the former owner had this work done by an A&P. I don't know if the case was doweled as was mentioned by other posters.

I think the morale of this story is to approach cylinder work with caution and ensure the all of the fasteners are appropriately torqued.
 
I agree. Our engine is in the shop now after we discovered a stud and a thru-bolt broken on the #3 cylinder. As they were broken above the cylinder flange, it was apparent that they had, at some point, been under-torqued. Also like yours, our case has fretted. We bought the airplane years ago through an estate and it had been sitting. We negotiated a price that would allow an overhaul if required. Since the engine had been overhauled 300 hours earlier by a well known shop, I doubt it was under-torqued there. I suspect someone, while it was sitting, removed a cylinder and improperly reinstalled it. In retrospect, it's apparent from scratches around those cylinder nuts that someone had had a wrench on them. Two lessons to be learned. First, the removal and replacement of a cylinder is not a casual maintenance procedure. Two, if you ever have a thru-bolt break, don't simply replace it. If the case has fretted, and you torque the new thru-bolt, your nice round bearing may not be round anymore!
 
mic2377 said:
I suspect what happened was the engine was turned over without torque plates installed, and the thru-bolts and cylinder studs were incorrectly retorqued. As a result the case seal failed and the case was subject to fretting.

.
Click to expand...

I doubt that. IMHO, removing cylinders does not cause this problem. I know it is one of Mike's favorite things to talk about, but it just doesn't compute logically if you understand the mechanics of how these engines are held together. If his logic was valid, simply assembling the engine would cause this. Case fretting and loosening through bolts have been a problem for decades and several fixes have been put in place to address it and it still happens. Two people posted on this thread that had the same issue and believe at least one of them had this issue with no cyl removal. While Mike is a reputable guy, he is NOT the last word on Lycoming engines and not 100% correct on everything he states on the internet. Lycoming themselves make no such statement and fully endorses field replacement of cylinders. We saying Mike knows more than them?

For the above, under torquing a through stud is totally different than just cyl replacement. I suppose one could make the argument that maintenance in and of itself creates the risk of a mechanic doing something wrong, but in this case it is not the cylinder replacement process that caused the failure, but was the failure to torque correctly. Just because a sloppy mechanic failed to torque a fastener correctly should NOT cause us to say that cyl replacement is bad. Instead we should say not correctly torquing a fastener is bad.

Larry
 
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Funny. I don’t see anywhere where I said it was bad. I said it shouldn’t be taken as a casual maintenance procedure. Also a RV “mechanic” is any living soul that can hold a wrench. A certain well known RV expert and author has written books trying to help us take ALL maintenance seriously.
 
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