Crankshaft Seal (split or not?)

[bnicolette]

Hi all,

 

My engine came back from the engine shop and it is running extremely well, but it is leaking like crazy.  Had to take it back to my mechanic and he discovered it was the crankshaft seal that was the culprit.  He called the engine shop and they are sending him a new seal but he wants to put on the split seal instead of the solid one.  Are there advantages/disadvantages to the split type other than they're easier to install?  How about longevity?  Needless to say it is disappointing that after spending all that money on the engine I have to have the plane back in the shop already.  Should I be worried about the rest of the work the shop did if the seal is leaking already?  Or is this a common occurrence and it just happens to be a spot of bad luck?

 

[jetdriven]

Use the one-piece seal. Yes you have to take the prop off and you really need to follow the directions on installing it in SI1342C to the letter.  We used Pliobond #20, but I would have preferred the Dow Corning 737 neutral sealant.  My mechanic also said that Permatex ultra black would be fine as a substitute, but I already got the Pliobond.

 

We did warm the seal in hot water to make it more pliable before stretching it over the crank flange. We also did not have the special tool and used a couple screwdrivers with a nice rounded shaft.  The warm seal helped here.

[N601RX]

The lycoming gasket kit actually includes both seals. I used the one piece seal also when overhauling my engine. Remove the spring, tape the crank flange good with electric tape to cover the sharp edges, warm the seal up in hot water lube everything up and it will actually go on easier than you think. I used pliobond also. You can order it from mcmaster.com if you can't find it locally.

If it still want go, you can always consult with your local gynocologist for additional ideas.

[jetdriven]

The solid seal is Lycoming 13792 from Aircraft Spruce.   18$ (It was 16$ a year ago). We bought the the Pliobond from McMaster Carr.  I would recommend the silicone RTV though. Pliobond is stringy and dries fast, its like contact cement.

[N601RX]

Make sure the crankcase vent tube is correct and not obstructed in any way. If the crankcase is building pressure, it will make the seal leak.

[tony]

Given where you are I would try tapping the existing seal in to see if it's not seated properly.  I assume your mechanic tried that already.  If you were overhauling you would certainly use the one piece seal but given where you are with this, I would try the split to see what happens before I went through the expense of removing the prop. 

[jetdriven]

You have to pull the prop either way.  Thats 1.5 hours labor anyways.

[Alan Fox]

See where the seal is leaking from , If it is leaking from the case side (outer) than pull it back , clean up the case real good , and reinstall with a bead of Proseal between the seal and the case , If it is leaking from the crankshaft , replace the seal with a one piece seal and again proseal will not leak ....You are pulling the prop either way , because you cant access the flange with the spinner back plate on ...A split seal is for amatuers that dont know how to do it right..... Do it right...... Check your breather , if there is a crankcase breather problem it will make a good seal leak....

[bnicolette]

It was definitely leaking around the "inside" of the seal.  Initially he wasn't sure and tried to seal around the case and the seal but it was still leaking, so he pulled the prop off the other day.  He broke one seal trying to get it around the flange I guess which I think is why he was thinking about using the split seal.

I haven't heard anything bad about the split seal but it seems as though the one piece is the consensus.  He has another one piece seal which he is going to try again but also has a split one ordered that will be here tomorrow as well in case try #2 doesn't go well.  He had the seal in a hot oil bath but doesn't have the proper tool to put it on.  Apparently though it can be done without the proper tool.

I try not to interfere with the maintenance end of things but I feel as though I need to suggest to him that I really want the one piece installed on the engine as opposed to the split type after reading the posts here.

Just really getting frustrated at this point.

[jetdriven]

Take two BAS* tools and that pin in the service instruction as shown, and pop the seal over the crank flange.  Grease the flange up really good, heat the seal in almost boiling water, grease the ID of it up real good too, then use the two BAS tools and the pin to get it over.  Work quickly. 

 

After geting the seal on the crank, install the spring, clean the OD of it really good , coat with sealer and pop it in.

* Big Ass Screwdriver

[N201MKTurbo]

I've done 4 of the solid seals. The hardest part is cleaning the crankcase, it needs to be like new. Bring the Coleman stove out to the hanger, boil a pot of water, turn off the heat and put the seal in the water and cover, let it steep for 10 minuets. Use the two BASs and it will go right on with surprisingly little effort. Put the spring back in and let it cool and shrink for about five minuets.

I wouldn't grease it, everything needs to be clean and dry before you put the sealant on. Use an acid brush to apply a thin coat of sealant on the case and the seal and work it into place. Work quickly so the sealant doesn't dry. Clean the excess sealant with alcohol.

[N601RX]

It was definitely leaking around the "inside" of the seal.  Initially he wasn't sure and tried to seal around the case and the seal but it was still leaking, so he pulled the prop off the other day.  He broke one seal trying to get it around the flange I guess which I think is why he was thinking about using the split seal.

I haven't heard anything bad about the split seal but it seems as though the one piece is the consensus.  He has another one piece seal which he is going to try again but also has a split one ordered that will be here tomorrow as well in case try #2 doesn't go well.  He had the seal in a hot oil bath but doesn't have the proper tool to put it on.  Apparently though it can be done without the proper tool.

I try not to interfere with the maintenance end of things but I feel as though I need to suggest to him that I really want the one piece installed on the engine as opposed to the split type after reading the posts here.

Just really getting frustrated at this point.

I would not feel bad at all about telling him which seal you want to use.  I'm sure your engine came from from the overhaul shop with a 1pc seal and you have every right to insist that a 1 pc be used when repairing it.  Is it covered under warranty?

 

After warming it up in boiling water it will actually go on rather easily.

[WheelPantsOff]

I'm bringing this back from the dead.  The seal on my M20J is starting to leak.  About 5 years and ~500 hours after overhaul.  Is the general consensus that the one-piece (LW-13792) or the Superior equivalent (SL13792) seal still the way to go? 

Edited August 8, 2025 by WheelPantsOff

[N201MKTurbo]

That’s what I would use.

 

[Mooney in Oz]

3 hours ago, WheelPantsOff said:

I'm bringing this back from the dead.  The seal on my M20J is starting to leak.  About 5 years and ~500 hours after overhaul.  Is the general consensus that the one-piece (LW-13792) or the Superior equivalent (SL13792) seal still the way to go? 

Due to unavailability of a one piece seal, my mechanic reluctantly fitted a split piece seal. A brief flight test revealed the oil leak still persisted.  Later after the one piece seal arrived, the prop was removed again and the 1 piece was fitted with no subsequent oil leak.

The one piece seal is the way to go.

[EricJ]

4 hours ago, WheelPantsOff said:

I'm bringing this back from the dead.  The seal on my M20J is starting to leak.  About 5 years and ~500 hours after overhaul.  Is the general consensus that the one-piece (LW-13792) or the Superior equivalent (SL13792) seal still the way to go? 

I just did this on my airplane with a one-piece.    A one-piece would be my recommendation.  It is easier with the tool and it is less likely to damage the seal than just using long screwdrivers or something.

[WheelPantsOff]

Thanks, guys.  Parts on order.

[Aaviationist]

Don’t forget to live it before installation. 
 

Installing dry will result in a very hard bit of rubber than will leak pretty quick. 

[WheelPantsOff]

I'm going to live it, lube it, and love it before installation.  And order a spare or two if it breaks it in two.

[EricJ]

2 hours ago, WheelPantsOff said:

I'm going to live it, lube it, and love it before installation.  And order a spare or two if it breaks it in two.

Lycoming has a good guide, Service Instruction 1324D, that is very useful for this task.    I think it'd be hard to break one in two, but it's definitely possible to goober up the edges if you're not careful.

[WheelPantsOff]

19 hours ago, EricJ said:

Lycoming has a good guide, Service Instruction 1324D, that is very useful for this task.    I think it'd be hard to break one in two, but it's definitely possible to goober up the edges if you're not careful.

Yeah, I found that one here and have familiarized myself with it.  It's a very well-written SI, considering that some I have read read like they're intended for engineers and not maintainers.

[N201MKTurbo]

21 hours ago, EricJ said:

Lycoming has a good guide, Service Instruction 1324D, that is very useful for this task.    I think it'd be hard to break one in two, but it's definitely possible to goober up the edges if you're not careful.

I have found them to be amazingly robust.

[N201MKTurbo]

The last one I did was on my rebuilt engine. I used Loctite 515. It stays workable for a long time and cures in the absence of air. It is not showing any signs of leaking.

[Yetti]

If it has been spinning for awhile the case may be oversized.   I believe my grumpy IA said they sell an oversized seal.

[WheelPantsOff]

To close the loop on this, the one-piece seal the A&P installed seemed to solve the leak.  I did notice that the oil return tube rubber couplings on the bottom of the engine were very loose and could be spun by hand.  The hose clams holding those in were tightened and a noticeable decrease in belly/gear door blow-by was evident after a few hours.