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IO360 Oil leak at cylinder jug base

Majorpayne317641

Well Known Member
I recently noticed some Oil dripping off my cowl so I pulled it to inspect. The #2 and #3 have a good amount of oil seeping from their bases that has made its way all over the bottom of the engine/exhaust/engine cowling. Any ideas? The engine has about 1100hrs. Nothing shows abnormal in CHTs, EGTs, fuel flow rates or power. Oil consumption was about 1 to no more than 2 quarts per 40hrs. I'm now at 2 quarts in 30hrs which explains the leaking. Can the o rings really just go bad? Or is there something else going on? The engine was zeroed back in 2012.
 
Are you sure it's the cylinder bases leaking or is it the oil return connector hoses from the rocker boxes? Those hoses will get hard and leak with time.
 
The base O ring is a pretty uncommon place for oil leaks. When mine appeared to leak from that area, it was actually the push rod tube seals that were the source, just hard to see the oil on the top side of the Cyl. Another area is leaking from the through studs in the case. That will appear as though the base gasket is leaking, as the oil comes out around the stud and then drips down the base flange. This is more common when the cases do not have sleeves to prevent case movement, though most have no idea if they are in the case or not.

Bad oil return hoses leak from the same area, but generally don't leave oil on the cyl flange. But that really depends upon air flow and how well the baffles seal. In a well organized baffle, air is flowing from the cyl base to the oil return tube, not the other way. Leakage from the spinner area can change the direction though.

Larry
 
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+1 on the pushrod tubes - I've been fighting a persistent small leak on my #4 exhaust.
 
For those with leaks at the inboard end of the pushrod tubes, the Lycoming school instructor taught us to turn the (green) seals inside out before installation, and they work better…..
 
#2 and #3 cylinders share the same thru bolt. While it is very unlikely, it is a good idea to check the torque on those nuts.
 
#2 and #3 cylinders share the same thru bolt. While it is very unlikely, it is a good idea to check the torque on those nuts.

While that is a good idea, they don't leak due to insufficient torque. They are interference fit bolts and excessive case movement causes wear between the stud and case hole. Once you get a thou or two of clearance between the stud and the case, they leak, unless the case was retrofitted for o-rings at the web joints where the through studs pass. That said, I believe these are slow leaks. If the OP is getting pooled oil in the cowling it is probably not from the through studs.

Larry
 
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Thank you for all of your responses. My A&P IA looked it over today and said the oil is so bad all over the bottom of the engine it is hard to tell where exactly the leak is starting from. I put about 44hrs of tach time since the last oil change and since I saw inside the cowling, which was dry then.

He told me to clean off all the oil from the engine and preform a ground run to warm the oil and find the source of the leak. I hope that this amount of oil is too much for a thru bolt leak. I didn't build the plane so I don't know if the baffling is sealed perfectly. I thought seeing some Oil at the base above the cylinders was a bad sign. I didn't notice any oil leaking from the push rod tube though. Here are 2 pics but they don't really reveal much other than the amount of oil. One pic is of the #2 and the other of the #3 from the bottom looking up.
 

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Wow, it looks like you need a case of brake cleaner to get all the oil off that mess. Ya, I know people use Stoddard solvent and all kind of cheap stuff. But, my money goes to the large cans of brake cleaner, electrical cleaner or the like.
Dries virtually clean and dry and fast.
You really need a black light and a dark hangar after you wash it to within a an 1/8" of it's life.
Most oil will glow green when hit with a black light. I use Phillips 20/50 and it is so green you could put cows out to pasture on it. When I started using a black light, I actually bought some oil leak detector dye. It is still on a shelf in my hangar somewhere.
I made the lucky mistake of shining the light on just plain oil.
Clean, clean clean, then look for leaks/weeps. Start engine for a few minutes and look again. Repeat and then repeat.
The black light trick has found the smallest of leaks.
Your luck will probably be just as good as mine after. Art
 
I think I will hit it first with Carbon X stain remover first to get the dripping oil off, then I will use brake cleaner like was recommended in the previous post. I will definitely try the black light trick, I just ordered one on Amazon.
 
Thank you for all of your responses. My A&P IA looked it over today and said the oil is so bad all over the bottom of the engine it is hard to tell where exactly the leak is starting from. I put about 44hrs of tach time since the last oil change and since I saw inside the cowling, which was dry then.

He told me to clean off all the oil from the engine and preform a ground run to warm the oil and find the source of the leak. I hope that this amount of oil is too much for a thru bolt leak. I didn't build the plane so I don't know if the baffling is sealed perfectly. I thought seeing some Oil at the base above the cylinders was a bad sign. I didn't notice any oil leaking from the push rod tube though. Here are 2 pics but they don't really reveal much other than the amount of oil. One pic is of the #2 and the other of the #3 from the bottom looking up.

Look for oil streaming from the bottom of the case up by the flywheel. A leaking front oil seal can be significant and the air flow will stream that oil along the bottom of the case all the way from the area by the alternator back to the oil dip stick tube.

The oil all over the servo makes me think front oil seal. Seems like too much oil for a through bolt leak. When you get a LOT of oil all over the bottom of the engine, front oil seal should be the first investigation, as it is high on the list of leakage points that can produce a lot of oil.

Larry
 
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I thought seeing some Oil at the base above the cylinders was a bad sign. I didn't notice any oil leaking from the push rod tube though.

throw some talc powder up there then blow off with compressed air. It tends to stick to oil and highlights the oil path. Due to gravity, it tends to leave only a limited trace between the PR tube seal and the flange base.
 
I replaced the front seal 100hrs ago and its not leaking. I washed down the engine and finished up with brake cleaner. Idling didn't produce any results.

Then a run up at full power for 1 minute produce a leak at the #2 cylinder near the base and front side of it. Checked again and the inside of the flywheel is bone dry. I did find some Oil at the #3 base near the bottom but not nearly as much and I wondered if it was from #2 and air blowing by.

Anyways I tried cleaning again, bone dry no grease or oil. Ran for 30 seconds full throttle and the first spot to appear was the front of the #2 just above the baffle at the base. See pictures. I know the builder replaced the #2 cylinder due to "low compression" I wouldn't have changed it for the compression he had but it is what it is.

Attached are some pics after the 30 second run. It highlights the locations really well. I took pictures all around that cylinder. I'm thinking it's the jug seal, but why give out now after 800 or so hours? Look at the engine cowl pic, it also looks like it originates at #2 and smears back.
 

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I replaced the front seal 100hrs ago and its not leaking. I washed down the engine and finished up with brake cleaner. Idling didn't produce any results.

Then a run up at full power for 1 minute produce a leak at the #2 cylinder near the base and front side of it. Checked again and the inside of the flywheel is bone dry. I did find some Oil at the #3 base near the bottom but not nearly as much and I wondered if it was from #2 and air blowing by.

Anyways I tried cleaning again, bone dry no grease or oil. Ran for 30 seconds full throttle and the first spot to appear was the front of the #2 just above the baffle at the base. See pictures. I know the builder replaced the #2 cylinder due to "low compression" I wouldn't have changed it for the compression he had but it is what it is.

Attached are some pics after the 30 second run. It highlights the locations really well. I took pictures all around that cylinder. I'm thinking it's the jug seal, but why give out now after 800 or so hours? Look at the engine cowl pic, it also looks like it originates at #2 and smears back.

Pooling oil after a 30 second engine run is a really bad sign. That is a serious leak! I don't see a bad oring at the base flange loosing that much oil in 30 seconds. It has to get past a tight fitting area and that o ring sees no movement and it not likely to disintegrate. I would be concerned about a case crack around the upper through bolt that extends to the left oil galley. The pressure in the galley will force the oil through the crack and I don't see how splash oil migrating through a crack can leave pooling oil in just 30 seconds. I fear you need to pull the #2 jug and investigate.

IMHO, you either have a relatively large opening to the inside of the case or the the leak source is exposed to pressurized oil. I just don't see anything else that can cause pooling oil in 30 seconds of running. Typical through bolt clearance issues weep oil, it doesn't pour out as your pics show.

I certainly hope that I am wrong and there is a simpler answer.

Larry
 
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IMHO, you either have a relatively large opening to the inside of the case or the the leak source is exposed to pressurized oil.

An interesting test would be to clean again and rig an adapter to add compressed air at the oil pressure port. Run 50 PSI into the oil system and observe. It may be easier to watch the oil appear without the prop spinning. This may give some better clues before pulling #2. This is based upon my theory that the oil is coming from a pressurized source and I could be wrong on that front, but it is the only thing that makes sense to me with the symptoms.

Larry
 
I did the black light test as I think Larry suggested. I found that the #2 does in fact have oil all the way around the front, bottom (although it may be because of gravity) and back of the cylinder base but not the top. I also found #3 has oil near the top, front and front base of the cylinder. Some of it ended up on the baffle near that area too.

This makes me think it may be a thru bolt. Or that the leak is finding its was to the thru bolt as a path to the other side (#3). The spot that has the majority of it is #2. I am pulling #2 this weekend to investigate. I will check the torque before unbolting it first. My A&P is helping me with the troubleshooting and has seen it under the black light with me, but he still doesn't know why it's leaking in that area. I've kept him in the loop from all of your great posts. I'll update when I have more info.

I am leaning on some sort of Crack in the case.
 
Opening an engine is like a box of Cracker Jacks - you never know just what you will find until you get inside. That is what I always found fun.
 
Oil leak

Pull #2 cyl back and look to see if o ring seal is theree , may have forgot to install it whe he put cyl. on , if no seal , you have to pull cyl. if seal is there you may have overhaul engine , send case to divico , they will find crack if thert is one , what is the total time on the engine.
 
It was overhauled by aero engines of Winchester back in 2010. I only have the 0 time logbook from that time and no previous time. I do know after doing research that this serial number started as a factory reman O320 in 1999 out of the lycoming plant when I checked the serial number. The overhaul only changed the bearings, cam lifters, cylinder assemblies and fuel system (plus the other standard stuff.)

This tells me I really have no idea how old the crank, rods and case are or how many hours they really have. My goal is to get the airplane flying again quickly. I see I probably don't have an option on my own overhaul to get a new crank (lead time) maybe a case, but I see they are 13k. I did not check lead time on that though. In the race car world, I wouldn't hesitate to just get a new case and all new rotating assembly for an overhaul, but I don't think I have that option with the lead times on some of these things. Anyone who has experience in this, I'm welcome to options.

I doubt they forgot the o ring because it was never leaking like this before and the jug was pulled at about 200 tach, I bought it at 900 tach and it now has 1100 tach.
 
The pics don't look like it, but keep your eye open for a crack in the case somewhere.

If you do find that it's a split line leak, cyl base seal, or even a though bolt, you *may* have some luck cleaning to bare, white metal and overlaying the area with Proseal. It worked once for me on a casing split line leak.

Rereviewing your pics, it's looking like a cylinder base seal. But that's a lot of oil. I would probably pull the jug.

2 cents of free Internet advice.
 
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I did the black light test as I think Larry suggested. I found that the #2 does in fact have oil all the way around the front, bottom (although it may be because of gravity) and back of the cylinder base but not the top. I also found #3 has oil near the top, front and front base of the cylinder. Some of it ended up on the baffle near that area too.

This makes me think it may be a thru bolt. Or that the leak is finding its was to the thru bolt as a path to the other side (#3). The spot that has the majority of it is #2. I am pulling #2 this weekend to investigate. I will check the torque before unbolting it first. My A&P is helping me with the troubleshooting and has seen it under the black light with me, but he still doesn't know why it's leaking in that area. I've kept him in the loop from all of your great posts. I'll update when I have more info.

I am leaning on some sort of Crack in the case.

The middle through bolts are what creates the rear #2 cyl attach studs and the #3 forward studs. The top through bolt bore through the webs is less than an inch from the bored passage in that web that goes from the oil galley (source of pressurized oil) to supply oil to main and cam journals, so a crack in the web (most highly stressed area of the case) could create a passage between the oil galley spur and the through bolt bore. The through stud only has about an inch of area in the middle that is thick to create the interference fit. After that inch, it necks down about a 1/16 or so, leaving lots of room for pressurized oil to flow out to the cyl base area (normally no oil in that area). The odd part here is that the interference fit in the middle should prevent oil flow between the halves, so a crack on one half of the web should not result in leakage on both sides. Suggest a very close examination of the center web halves in the area that the top bolt passes through, as well as cranking on the top through bolt to see if it is loose/cracked. It should require a decent amount of torque to move. Also, important to note that there are different types of through studs. Some are true through studs (pressed in and cyl nuts hold torque on both sides), however some are threaded into the case on one side.

Larry
 
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E4BA19B9-46DB-47E5-B0B1-8B2B9AF46BBD.jpg

I was just at DIVCO, the crankcase overhaul company in Tulsa this morning. Chuck, the president, showed me a number of cases with cracks that start in the lower corner of the cylinder mounting boss, and go all the way around under the cylinder to the other bottom corner. He said he had a cylinder somewhere that was turned in by a farmer that still had that piece of crankcase bolted to it - the thing blew of the engine and was found in a field. I mentioned this thread to him, and he said that with his experience of thousands of cracked cases, he wouldn’t be surprised if you had a cracked case in this area…..
 
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I got the #2 cylinder off. I see no cracks on the base of the case. I do see a large amount of oil draining from the top rear bolt. I think this may be a sign of a Crack inside the web near the pressurized oil galley. See pictures.
 

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I got the #2 cylinder off. I see no cracks on the base of the case. I do see a large amount of oil draining from the top rear bolt. I think this may be a sign of a Crack inside the web near the pressurized oil galley. See pictures.

That would be my guess as well. Highly likely that any crack in that area will be visible on the interior. So stick some mirrors or a borescope in there and examine the upper web area and see if you can find it. Rotate the crank to get the offset weights on the crank out of the way.

Good news is that many webs have cracks and many of them can be re-welded by Divco under the flat $1000 overhaul. They told me that finding web cracks on 540's is the norm, not the exception. Hopefully yours can be repaired.

I would also remove the #3 hold down nut on the other side of that through bolt and see if any movement can be detected.

Larry
 
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So yeah….they do scrap a lot of cases at DIVCO (here’s a shot of their storage area for red-tagged hardware)….

C9137422-1453-431A-9BDF-82B29F5FACF2.jpg

The good news is that this is a drop in the bucket compared to the number of cases I saw with weld repairs that were waiting on re-machining. I learned a bunch about cases and case repairs yesterday (for an upcoming Kitplanes feature), and one of the little things I see in MajorPayne’s photo is that it is an old style case, which DIVCO told me is more prone to cracks. Good news - they can fix an awful lot of cracks!
 
There was no movement of the thru bolt, it was stuck pretty good. I needed to use the nut and threads to slowly pull it through the case. When I pulled the bolt a bunch of oil poured out with it.
 

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Take a look at my experience with this same leak. I have about 200 hrs on since doing Lyc SI1290 and It's still bone dry :) I consulted with usual engine gurus here and called Divco.

https://vansairforce.net/community/showthread.php?t=191165
https://vansairforce.net/community/showthread.php?t=191860

The only thing I did different that the SI called for:
  1. instead of using a reamer to clean up the bore I used 1/2" bore brushes of progressive grit (200-800). It probably didn't need it but it was hard to tell how clean it was.
  2. I used a P2 rather than the P1 through bolt right way based on the extra .001 the bore brush took off
  3. I lightly coated the bore and associated part of the thru bolt with Loctite 518 before installation
  4. Since I used bore brushes that have a cutting medium, I made sure the bore was flushed several times and I pre-oiled the engine with about 6 quarts of new pressurized oil to flush any contaminates that made their way between the bearing and crank

I suspect the reason the oversized thru bolt tends to work because a normal thru bolt may not have much of an interference fit. The aluminum bore grows larger than the steel thru bolt and the interference is lost at normal operating temps. If there's any case fretting that provides a path for oil, from the main to the bore, it will get past the thru bolt also.

New cases are doweled and o-ringed so they don't have this issue. Dowels provide rigidity and o-rings seal off the oil path.

Hoping my fix gets me to next overhaul...so far, so good.
 
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Take a look at my experience with this same leak. I have about 200 hrs on since doing Lyc SI1290 and It's still bone dry :) I consulted with usual engine gurus here and called Divco.

https://vansairforce.net/community/showthread.php?t=191165
https://vansairforce.net/community/showthread.php?t=191860

The only thing I did different that the SI called for:
  1. instead of using a reamer to clean up the bore I used 1/2" bore brushes of progressive grit (200-800). It probably didn't need it but it was hard to tell how clean it was.
  2. I used a P2 rather than the P1 through bolt right way based on the extra .001 the bore brush took off
  3. I lightly coated the bore and associated part of the thru bolt with Loctite 518 before installation
  4. Since I used bore brushes that have a cutting medium, I made sure the bore was flushed several times and I pre-oiled the engine with about 6 quarts of new pressurized oil to flush any contaminates that made their way between the bearing and crank

I suspect the reason the oversized thru bolt tends to work because a normal thru bolt may not have much of an interference fit. The aluminum bore grows larger than the steel thru bolt and the interference is lost at normal operating temps. If there's any case fretting that provides a path for oil, from the main to the bore, it will get past the thru bolt also.

New cases are doweled and o-ringed so they don't have this issue. Dowels provide rigidity and o-rings seal off the oil path.

Hoping my fix gets me to next overhaul...so far, so good.

Thank you for the add. I borescoped the hole and this case already has bushings installed at the two case halves. Did your bolt come out easily? Mine required pressing to remove; pretty much the entire length of the buldge required a pressing operation to get it out of the hole.
 
How does this look in real life?

When you clean the case and look at this area is it still suspicious? That surface sure looks like the barrel was working against the case, and the gray goo on the through bolt appears to be aluminum slurry. Movement would is consistent with the leak, and if all was tight/torqued before dissemble, it would seem to warrant deeper inspection methods.

Screen Shot 2022-10-09 at 8.25.51 AM.png
 
Thank you for the add. I borescoped the hole and this case already has bushings installed at the two case halves. Did your bolt come out easily? Mine required pressing to remove; pretty much the entire length of the buldge required a pressing operation to get it out of the hole.

With steal dowls I don't believe you can do the SI1290 but I would read it...you may be able to oversize to P1 thru bolt.

Mine did require some effort to remove...I used a stack of washers...one aluminum against the case to prevent marring, normal nut to work it out. It didn't take much torque (maybe 10 lb-ft) to make its way out
 
With steal dowls I don't believe you can do the SI1290 but I would read it...you may be able to oversize to P1 thru bolt.

Mine did require some effort to remove...I used a stack of washers...one aluminum against the case to prevent marring, normal nut to work it out. It didn't take much torque (maybe 10 lb-ft) to make its way out

I would not recommend this approach. A through bolt that has loosened up a bit due to fretting is not going to pour oil out; Just doesn't make sense. I remain of the opinion that the amount of oil produced in 30 seconds of engine running points to the leak source being exposed to pressurized oil. IMHO, a case tear down is in order to confirm the source. I, of course, could be wrong, but do you really want to risk flying around with a potentially significant crack in the case webbing?

I suppose it is worth a shot, as it will likely still leak after the upsizing if it is a crack. That said, how do you know if this case has sleeves and o-rings. The pics show a clean metal spot in the center, which makes me think it has o-rings, though I don't have enough experience to interpret that. As long as the oring is intact, you cant really leak oil due to a loose fitting through bolt without a crack somewhere. The orings are orange. Did you by chance see that with the borescope? There should be 1/16 to 1/8" of oring exposed to the internal cavity. May need to clean the oil out of the bore before you can see it.

I would call Divco and get their opinion. I am guessing they have seen it all and will likely have good advice.


Larry
 
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I found the problem. The upper web that was leaking has exhibited case fretting. I called divco and talked to them about what I was seeing. The O ring was damaged from the fretting which may have explained the massive leak. It was only a matter of time for when this would occur, more than likely from the previous owner's cylinder replacement 700hrs ago. Notice the machine marks one should see that is in one picture. You can see this on all but the one web. The web that was leaking has a frosted appearance, the second picture. Divco said this is a sign of fretting.
 

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There are so many times that an interesting situation like this never gets the results reported or finalized. Thanks to Majorpaine* for keeping us updated with photos and letting us know the conclusion.
By the way, is that "lip" on the perimeter of the fretted surfaces actual metal or just crud?
 
The gray oil on that thru-bolt was aluminum rich oil from the fretting. The nut should have been very loose if checked. Were you able to check torque prior to disassembly?

That gray matte surface was also showing under the barrel flange. Fretting there too.

RadioFlyer . . That looks like a sealant lip, but surely a lot of erosion there. Sealants should never be used on surfaces prone to shear and separating loads. Abutment of the joint is compromised. Remember that Conti had fatigue of barrel studs if RTV is used under the barrel flange. Many highly loaded areas like this can not have paint or the joint will fail. Just simple engineering of simple joints.
 
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I found the problem. The upper web that was leaking has exhibited case fretting. I called divco and talked to them about what I was seeing. The O ring was damaged from the fretting which may have explained the massive leak. It was only a matter of time for when this would occur, more than likely from the previous owner's cylinder replacement 700hrs ago. Notice the machine marks one should see that is in one picture. You can see this on all but the one web. The web that was leaking has a frosted appearance, the second picture. Divco said this is a sign of fretting.

GREAT investigating and reporting. That web face is in bad shape. The last overhaul most likely did not include crankcase machining. While not required it is a prudent thing to do on those little Lycoming engines.
 
I did not check the torque with a torque wrench. It did take effort to get the bolts off. I did notice that not all bolts took equal effort in my calibrated arm if that makes sense. I don't think the builder torqued the #2 rebuilt cylinder correctly. The nuts and bolts look ancient, not 12 years old. I don't think the SMOH builder used new fasteners at all.
 
I found the problem. The upper web that was leaking has exhibited case fretting. I called divco and talked to them about what I was seeing. The O ring was damaged from the fretting which may have explained the massive leak. It was only a matter of time for when this would occur, more than likely from the previous owner's cylinder replacement 700hrs ago. Notice the machine marks one should see that is in one picture. You can see this on all but the one web. The web that was leaking has a frosted appearance, the second picture. Divco said this is a sign of fretting.

That makes sense. YOu can see where the fretting and broken o ring allowed pressurized oil from the journal cavity to reach the through stud bore.

The pics show what appears to be almost 1/16" of worn material off of the web. Seems like an awefull large amount of wear and makes me wonder if something was done incorrectly at one point in it's history. I hope there is enough meat left for Divco to re-work it.

Good luck.
 
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I found the problem. The upper web that was leaking has exhibited case fretting. I called divco and talked to them about what I was seeing. The O ring was damaged from the fretting which may have explained the massive leak. It was only a matter of time for when this would occur, more than likely from the previous owner's cylinder replacement 700hrs ago. Notice the machine marks one should see that is in one picture. You can see this on all but the one web. The web that was leaking has a frosted appearance, the second picture. Divco said this is a sign of fretting.

This is interesting, I thought the steel dowels were supposedly extend to both halves? Isn't that suppose to be the reason of the dowel SI...to create rigidity between the halves and prevent fretting?

Maybe there aren't any dowels at all???

That fretting makes me wonder how long my SI1290 fix is going to last. Thought my oil leaking was really clean and didn't contain any aluminum "slurry"
 
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Yes, it is a helpful thing that aviation motor oil has a fluorescent dye in it for leak detection. I used to use Aeroshell 100 for flow visualization work in the wind tunnels at work.


Wow, it looks like you need a case of brake cleaner to get all the oil off that mess. Ya, I know people use Stoddard solvent and all kind of cheap stuff. But, my money goes to the large cans of brake cleaner, electrical cleaner or the like.
Dries virtually clean and dry and fast.
You really need a black light and a dark hangar after you wash it to within a an 1/8" of it's life.
Most oil will glow green when hit with a black light. I use Phillips 20/50 and it is so green you could put cows out to pasture on it. When I started using a black light, I actually bought some oil leak detector dye. It is still on a shelf in my hangar somewhere.
I made the lucky mistake of shining the light on just plain oil.
Clean, clean clean, then look for leaks/weeps. Start engine for a few minutes and look again. Repeat and then repeat.
The black light trick has found the smallest of leaks.
Your luck will probably be just as good as mine after. Art
 
This is interesting, I thought the steel dowels were supposedly extend to both halves? Isn't that suppose to be the reason of the dowel SI...to create rigidity between the halves and prevent fretting?

Maybe there aren't any dowels at all???

That fretting makes me wonder how long my SI1290 fix is going to last. Thought my oil leaking was really clean and didn't contain any aluminum "slurry"

From my understanding, the hollow dowels in the through stud bores were only used on the narrow deck engines and some early WD transition engines. After the 70's, interference fit (Lyc calls them body fit) through studs were used to hold things together and stop movement. In those cases, oversize through bolts were required when wear eliminated the interference fit. The earlier through studs were threaded into the left side of the case. The fact that the OP was able to draw the through studs out, implies that they are body fit through studs.

Once the interference fit is gone, they will start fretting. Hard to say in your case how much fretting happened before you replaced the through studs. I would expect taht the fretting starts long before things are sloppy enough to start pouring out oil. The OP's data here shows that. Oil only recently started to appear, yet significant fretting wear has already occured.

Larry
 
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