Bartman

Leaking engine case thru bolt

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A couple of years ago I found the cause for an annoying leak, the top bolt that goes all the way thru leaking around the nut.  I let it go for a long time but this past annual we decided to remove the nut and put some sealer on it.  Lets just say it leaked more...a lot more but on the other side.  We pulled both nuts and put sealer on both sides but now it is leaking and coming out at the base of the cylinder on the opposite side and more annoying than when I started. Leaks about 1 quart in 4 hours and enough to make a mess on the nose gear every time I park and no it's not the magneto or anything else.  I am currently at 1950/2000 hours and 5600 hours total on the original IO-360 A3B6D and compressions are great with clean oil screen and oil filter.  My plan has always been to keep running based on condition and my AI/AP is supportive, but the oil leak has got to go.

Here's the question ???  I have considered pulling the 2 opposing cylinders, apply sealer on the thru bolt and keep on flying. If the camshaft is questionable then I'm not going to rebuild a 1977 vintage case and I'll go with a roller cam upgrade. But if the camshaft looks good why not pull all 4 cylinders, have them serviced and keep on flying with new rings and gaskets?  I'm going to do something, just looking for some advice due to the age. 

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The previous owner of my plane overhauled the 2400hr engine just because of oil leaks, so you’re not alone if that is what you’re thinking.  

I had leaks on the case half seam and through bolts at the top of the engine, which I remedied.   The cylinder through bolts are a bit more invasive.  I’d be inclined to try and seal the front ones and see how it goes. That sounds like an excessive amount of oil loss.    The key to getting any sealant to work is spend plenty of time doing a thorough removal of oil everywhere possible.   I used many q-tips with acetone.  Seems like I used MEK also, but can’t remember.   I used a purple loctite product, can’t remember the number, but someone on here will recall which one.  

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Speak to an engine shop for guidance, but I believe you'll learn that you need to replace the thru bolt. They are available in oversize, something like .001", .002" and .005". O-rings aren't allowed on Lycoming thru bolts. Sealant anywhere between the case/cylinder/nut  is forbidden since it leads to torque failures. Even paint on the case at the base of the cyl or below the nut leads to torque failures.  Be careful since a torque failure will lead to poping cylinders nuts and a potential inflight loss of a cyl. Engine shop should be able to give you and your A&P good advice.

Since it leaked on the opposite side, just in case I'll add its critical that when a thru bolt is torqued, it has be properly wet torqued from both sides with 2 people. 

Edited by kortopates
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It is best to remove the cylinders on both sides. You can get the through bolts out with a hardened nut and a stack of washers. Use a steel plate against the case so you don’t mar the case. Get a long brush the size of the hole and clean it real good then measure the bore with an internal plug gauge. Make sure you get the correct size through bolt and reamer, you don’t want to screw this up.

Read the procedure in the engine manual for the correct fit!

clean and inspect the bore after reaming with a borescope. Make sure there are no scores, per the manual.

Get a long grade 8 nut, the kind you use for a turnbuckle. Tap on the nut to drive the bolt back in. When it is through enough to get a nut on it, put the steel plate with a hole in it on the case and draw it in till it is even. Reassemble your engine.

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Nothing describes an important bolt like Paul and Rich!   :)

Thanks for sharing the details, gents...

Best regards,

-a-

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I’ve actually done this twice on different engines. Both were successful and leak free. 

It helps to work for a place with a full machine shop so you can borrow the measurement tools and reamers.

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Thanks to everyone. I think we will pull at least one cylinder and look at the camshaft and if it looks good then decide what to do from there. I have a trips planned the next couple of months and in the meantime we will speak with an engine shop and make plans. It just so happens our AP/IA also runs a full machine shop as his main business so tools and expertise are not an issue. He is also a pilot and maintains a handful of planes at our field as a side hobby job and we are lucky to have him just like Mooneyspace is lucky to have knowledgeable members like yourselves and others. 

We will tackle this in the fall and I’ll post an update. Thank again !

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I’ve actually done this twice on different engines. Both were successful and leak free. 
It helps to work for a place with a full machine shop so you can borrow the measurement tools and reamers.

Helps to have the skills as well, if it were me I would have a very experienced AP do this while I wrote the check.


Tom
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The up side of this is the parts cost is less than $100 for the whole job. You are looking at ~10 hours of labor.

Some mechanics will always replace the rings if they pull a cylinder, this will drive up the parts cost.

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Long time ago there was a small airline that had  Navajos and when they got a leaky engine at the top center case split line they used 5 minute epoxy on it to hold the leak in. They just cleaned the seam with MEK and smeared the epoxy on the case split. Seemed to work fine until overhaul. Just thinkin'

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1 hour ago, cliffy said:

Long time ago there was a small airline that had  Navajos and when they got a leaky engine at the top center case split line they used 5 minute epoxy on it to hold the leak in. They just cleaned the seam with MEK and smeared the epoxy on the case split. Seemed to work fine until overhaul. Just thinkin'

Yeah mine has that on the top center case split since purchase in 2007.  I don't remember what kind of material it is but it is hard and smooth and documented in the logs and was done at an engine shop about 200 hrs on this rebuild.  There was documentation of having to split the case a couple hundred hours after rebuild due to leak at that seam.  It does not leak at the top seam in the past 1200 plus hours. 

My current problem started when we put some dye in the oil and I saw that was the only place on the whole engine with a single drip with the blacklight so we thought it would be an easy fix.... NOT !!!  The leak wasn't that bad before, just a nuisance, but now it drips on the nose wheel and although it has been steady for about 50hrs I still don't like it.  Still considering if the camshaft looks good we hone all 4 cylinders and service the valves and maybe new rings and keep on flying on condition.

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