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Lycoming Crankshaft Leak Between the Crank and the Seal

Nived17

Active Member
Hey VAF-ers,

So I decided to come here and post some recent findings on my 290 SMOH (completed in Spring 2019) O-320-E2D on my RV-4. I bought the airplane in January 2016. It had around 900 SMOH. Flew the snot out of it the first two years and always had a damp engine during those years. A drip was always found on the starter and alternator bracket and the airbox was always greasy along with the carb. Cylinder work was needed in 2019 and I elected to completely overhaul it at that time. It was done at a certified shop in TX yellow tags on all reused components. From about hour 30 on the new engine, I noted that the bottom of the engine was damp yet again with oil. At that time, I was working as an engineer at Lycoming engines so I wasn't too concerned. Surely they have a fix for this and I would get discounted parts if it got worse. So I flew it some more with a continually slightly damp lower engine. I then proceeded to get laid off from Lycoming along with 30% of employees at the company in July 2020 due to covid cutbacks. (bye bye discounted parts and easily available solutions. I knew I should have bought a new engine while I was there...)

Fast forward now to January 2021. I moved to Milwaukee, WI and did a little sub zero flying out here and found a more significant amount of oil now leaking on post flight inspections having switched to a multi viscosity oil from aeroshell 100W. I heavily cleaned and leak checked it and determined it was coming from the crankshaft seal. I inspected the superior split seal which was installed at overhaul with plyobond. It was well adhered to the case and absolutely not leaking around the seal... uhoh... ya you see where this is going.


Turns out that the leak is coming from between the seal and the crank itself! How could this be?! Having worked for Lycoming, I immediately went to the O-320 Table of limits and noted that the diameter interacting with the seal uses the same leader line on the new part print as the front main bearing (2.375" in diameter). I took a measurement on my crank in the area that interacts with the seal. It measured 2.368" :eek: Not good. I called a lot of friends at Lycoming and had a lot of talks. It would appear that this diameter at the seal can be polished/ground up to .010 under nominal but it is EXTREMELY convoluted in the literature and table of limits. I called the repair station that yellow tagged the crank and they verified that it measured 2.368 as well and that they did not grind or polish that area at all during my overhaul work. (This is the 3rd run on this crank). So now what?

I have all the tools required and a few LW-13768 seals and I elected to simply install a new solid seal per SI1324C and hope for the best. I completed the job last night and left a heat lamp on my work to let the Dow Corning 737 set up before leak checking later this week. After completing all this work I, have not yet done a leak check while I am writing this so I will be sure to do a follow up post. I wanted to note a few things though that I have learned so far to help others:



1. - Ask your repair shop and overhauler what that dimension the crank measures in the area that interacts with the crank seal overhaul! I never would have guess how large of a pain it would be.

2. - Lycoming does not design a seal that will work with a crankshaft that is smaller than 2.374" OD in the area of the seal... Even though it still meets overhaul limits!:mad: I am not happy about this.

3 - What are the solutions? I did not try this yet but I wish I had thought about this before completing the job last night. I read another thread here where someone recommended cutting a few coils off the female side of the inner spring that goes in the crank seal before twisting it together and installing it in the seal on the engine. From what I can see, this is the best solution and will help apply more pressure on the undersized crank.




At least I now know another cheaper fix to try if this continues to leak before I have to pull the engine and split the case to replace the crank. If anyone wants to see pictures I will happily email them as it is easier than trying to post them here.



...all to prevent a few drips of oil. Some days airplanes are really frustrating.
 
Yet by another name

Leak-a-sarus..... aka lycoming. Lots of money to be made chasing and trying to fix mild leaks. Don’t blame you for wanting a leak free lycoming. I was told it is a matter of time for most, but generally at the machine case joins. Thanks for sharing.
 
Leak-a-sarus..... aka lycoming. Lots of money to be made chasing and trying to fix mild leaks. Don’t blame you for wanting a leak free lycoming. I was told it is a matter of time for most, but generally at the machine case joins. Thanks for sharing.

If I showed you the leak here in Milwaukee with the thinner oil, you wouldn't have flown it either. It wasn't really a minor leak anymore. I hope the new seal gets me through the winter before I need to take it off and shorten the spring inside another seal. Here's to hoping.
 
yep, annoying stuff...

#3 sure is (woz) the best solution...
Another one would be to install the 2 piece seal, permits one to apply some sealant on the perimeter of the seal for a better clamping on the crank, next problem is in the mating half seals...
 
Try Continental SB on leaking crankshaft seal

I had a similar issue...tried 2 or 3 seals and shorted the inner spring...still had a slight leak The fix for my engine was to put a helix in a counter clockwise direction on the shaft where the seal sits....you can do it with just the seal removed and the proper size Emory cloth.

Should be a post with that SB from Continental on the forum from about 2018. If not, I can email it to you....

Paul
 
I had a similar issue...tried 2 or 3 seals and shorted the inner spring...still had a slight leak The fix for my engine was to put a helix in a counter clockwise direction on the shaft where the seal sits....you can do it with just the seal removed and the proper size Emory cloth.

Should be a post with that SB from Continental on the forum from about 2018. If not, I can email it to you....

Paul

Here is the link that Mahon shared with me when I had the leaking seal issue....

http://aeronca.org/ContinentalSB-M76-4.pdf
 
Here is the link that Mahon shared with me when I had the leaking seal issue....

http://aeronca.org/ContinentalSB-M76-4.pdf


Thanks Paul. I’ve read a bit about scoring the crank like you mention in the SB. I’m just worried that my crank being small causes more issues and removing material from that area doesn’t seem like a good idea to me. Do you have any idea how small the diameter on your crank may have been if it was smaller than 2.375”?
 
Devin,
I hate offering advise like this but sometimes in a situation like this a trick is required. If all else fails with your new non split seal. Take a cotton swab dip it in transmission fluid. Run it around the crank shaft against the seal where they come together. Let it sit for a day or two. The fluid will slightly swell the seal. It works in some cases. When I started with the airlines a gazillion years ago the old timers used this trick for leaking strut seals on landing gear. YMMV Good luck.
Ryan
 
good tip

Devin,
I hate offering advise like this but sometimes in a situation like this a trick is required. If all else fails with your new non split seal. Take a cotton swab dip it in transmission fluid. Run it around the crank shaft against the seal where they come together. Let it sit for a day or two. The fluid will slightly swell the seal. It works in some cases. When I started with the airlines a gazillion years ago the old timers used this trick for leaking strut seals on landing gear. YMMV Good luck.
Ryan
That's pretty clever. Could you imagine a book of tips and tricks like this? It would be really valuable.
 
Thanks Paul. I’ve read a bit about scoring the crank like you mention in the SB. I’m just worried that my crank being small causes more issues and removing material from that area doesn’t seem like a good idea to me. Do you have any idea how small the diameter on your crank may have been if it was smaller than 2.375”?

I can not address your dimension issues, but don't discount the proven value of the surface finish modification. It is quite effective and not limited to an aircraft application. That is a basic engineering parameter of good sealing. You would not be able to measure the material removed even with air gauging.

After the surface finish and spring adjustments, you might consider the anti-splat blow-by "injector" into the exhaust. Do your homework on the maintenance requirements before you decision just to know what you are getting into. It will certainly leave the engine dryer from non-oil pressure related issues.
 
Thanks Paul. I’ve read a bit about scoring the crank like you mention in the SB. I’m just worried that my crank being small causes more issues and removing material from that area doesn’t seem like a good idea to me. Do you have any idea how small the diameter on your crank may have been if it was smaller than 2.375”?

Sorry,

I don't recall the measurement of that section of the crankshaft...but when I sent out my crankshaft to be yellow tagged they just polished it up...and required bearings were 10,000 thousand oversized...

Keep us posted on what your solution. Note: I also did the Anti Splat crankcase vacuum mod that runs the breather tube into the exhaust (which is a great mod)....but still had a little bit of leaking at the crankshaft seal....until I did the Continental SB procedure.
 
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