What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Causes of Crankshaft Seal Leaking a little oil

Triumph1974

Well Known Member
I am still in phase 1 testing and have been having an issue with the Crankshaft seal leaking a little oil...basically not long into phase 1 testing. The leak is always between the crankshaft and the seal (my crank is 10/1000 undersized). I have changed the seal several times, but am beginning to think it may be an issue of to much pressure in the crankcase, but I know I don't have a breather tube restriction issue.

Here is some background:

An A/P friend and I overhauled the engine, and had all the existing cylinders/values done by a local shop. New crankshaft thrush washers where installed etc.

I have the Ney Nozzle STC which sprays oil up on the camshaft when ever the engine is running...

#2 CHT is always about 30 degrees cooler in cruise that the other 3 which are 1-5 degrees apart , but on decent all the cylinders are within a couple of degrees of each other.

When hand cycling the engine cold I notice that one cylinder is "weaker" as the others is not as much effort required to pull the prop through on the one cylinder

Did an simple test of removing the top spark plugs on #1 and #2 and there is definitely less air blowing in your face out the #2 spark plug hole when rotating the prop on the upstroke to TDC position.

I did install the crankcase vacuum system from AntiSplat hoping it would solve the leaking seal and ran it for 3 hrs the other day and noticed that the bypass safety had a very small amount of oil film on top of the exhaust pipe which is a little below where the bypass hose terminates....so I am thinking the bypass was activated at some point due to over pressurization, and there was a small amount of oil coking one one side of the vacuum pipe that goes into the exhaust after 3 hrs of run time....so it looks like a lot of blow by oil is getting out of the engine, but not enough to say the engine "uses oil" beyond normal...and I am likely still breaking the engine in...it has 33 hrs.

Questions:

What is the best way to see if a bad or weak cylinder is the issue and causing
over pressurization of the engine case, and is there anything other than a broken ring that can cause over pressurization, and what are the best ways visually tell if is a ring is broken prior to removing the cylinder?

What is best what to measure crankcase pressure, and what is a normal pressure reading and can this be done by hand rotation, or does the engine need to be running?

Thanks for any advice.

Paul
RV7A Phase 1 testing O-360
 
In my opinion, it would take a LOT of blowby to pressurize the crankcase enough to cause an oil leak. If I remember, the breather outlet is 3/4" and that will move a LOT of air before creating a significant pressure in the case.

Have you run a compression test or leak down? The fact that you have a noticeably reduced amount of air pressure/volume from one cylinder in the test you mentioned is very concerning. It would take a significant problem to create that effect, not just poor ring seals or a broken ring, though two broken rings would; possibly a valve issue. If you do have two broken rings in #2, that would explain the performance issue (reduced CHT) and would put a lot of pressure in the crankcase. IMO, one broken ring will not put enough pressure in the case, to make a seal leak, Ask anyone who does overhauls how common it is to find a broken ring. Many do and do not have leaks at the crank seal.

I would conduct a leak down test on the problem cylinder before your next flight.

Some seals just leak without pressure - defective seal, bad installation, etc. I would not assume it is crankcase pressure causing it until the leak down shows that you have a problem bleeding air in the crankcase. If your leak downs are good, it seems unlikely that your leak is due to crankcase pressure.

It is not uncommon to break a ring during installation and it seems realistic that the error could easily have broken both. It is also possible that the wrong rings were used for #2 with too small of a ring gap. (e.g. overhauler says they are bored 10 thou over, but worker, in error, only hones the cyl you put on number 2, with no boring. Builder puts in 10 over rings - Bang, cracked rings or broken lands in #2). They would have then both cracked and the first full power run with the engine up to operating temps.

Larry
 
Last edited:
How do you know the crankshaft seal is leaking? Just because there's oil up there doesn't mean it's coming from the seal. I changed mine once because I was "sure" it was leaking, only to find out that the oil on the front of the crankshaft was coming from a rocker cover gasket. Oil blows everywhere from a leak.
 
You can always pressurize the crankcase with a rubber stopper and tube in the breather. Maybe 10" of water, you can blow that much and put some snoop on the crank seal. That is the way it is done in a factory (engine) environment.
 
Last edited:
Update on leaky Crankshaft Seal

Thanks for the info guys - very helpful. I could see some oil between the shaft and seal, and was having a little oil inside the starter ring wheel, so I am fairly sure it is the crankshaft seal that is leaking.

This evening we did a cold compression test and all was good...the #2 cylinder was actually 80/80, and after the cylinder check when I hand rotated the prop no weaker cylinder was found. ..so perhaps the other day the #2 rings just happened to rotate around so the gap on both lined up to each other...

Will do a test flight later in the week and report back...maybe the newest seal that was installed over the weekend will be leak free....
 
I could see some oil between the shaft and seal, and was having a little oil inside the starter ring wheel, so I am fairly sure it is the crankshaft seal that is leaking.
That's exactly how it looked when my rocker cover gasket was leaking. Good luck.
 
If you are replacing the seal, make sure it is a one piece seal. I have never had any luck with split seals. pain to install but worth the effort.
 
I went through 3 seals in the first 2 years of flying. The initial one leaked a lot. It wasn't glued in very well when I replaced it, so I thought that would be the end of the leakiness. The second one was much better, but it still left a light ring of oil on the cowl inside. Whenever I had the cowl off, there would be a nice line of oil around the starter ring periphery. When the annual came around I decided to try another seal. This one has performed much better. No more oily ring on the cowls! I don't know if I just got better at installing them (the engine builder did the first one), but my experience is that the seals themselves can vary a bit in how well they keep the oil in. They aren't difficult to put on. Get the correct DOW sealant, heat up the seal, stretch it over the hub and let it shrink back into shape. Then put the spring in, clean everything thoroughly and glue it in place. Wait a day for the sealant to cure before moving the hub and putting the prop back on.
 
This evening we did a cold compression test and all was good...the #2 cylinder was actually 80/80, and after the cylinder check when I hand rotated the prop no weaker cylinder was found. ..so perhaps the other day the #2 rings just happened to rotate around so the gap on both lined up to each other...

Having the two ring gaps line up does materially change compression. The air easily moves about to find the gaps.

Just keep an eye on it to be sure the low compression issue doesn't return.

Larry
 
I am still in phase 1 testing and have been having an issue with the Crankshaft seal leaking a little oil...

I had this issue once after changing where the breather tube exited in the cowling. Initially I did not have an issue until I changed the breather tube routing and exit location. After that I suddenly had a lot of excess oil in the forward cowling. I came to the conclusion that I must moved the exit to a location where there must be a higher positive pressure.
- I then moved the exit so it is low between the exhaust stacks (RV6). For the lower part near the exhaust stacks, I used a bendable but rigid stainless water line connection normally used for a water heater connection (I cut the integral fittings off). I still had some oil weeping but much less.
- Some time after adding the lower breather exhaust tube, I removed the prop and replaced the one piece seal. I've put about 300 hours on it since and have not had any visible leakage since.
 
Last edited:
Update on Crankshaft Oil Seal leak

Thanks everyone for the responses. Here is an update to the situation....

I put a new one piece crankshaft seal from Superior (all the others were the Lycombing/Parker brand seals), a while back and the oil leaking slowed significantly...just a little oil on top of the air filter box now. At this time I also installed the Aero-Splat crankcase vacuum system that has the safety bypass valve vs. the straight breaker tube. I have ran the engine about 15 hrs with this seal on and vacuum system.

Since it is time to change my oil from the break in mineral oil to the ashless oil, I decided take off the prop to hook up a manometer tube and pressurize the engine with about 2-3 or less PSI - or about 12 " of water column in the tube and spray soapy bubbles on all the crank seams to see if I find any other leaks, but the engine has held pressure all night, and is still holding even with the water column pressure increasing during the next day time with the rising temps.....so it looks like the seal is the only source of the leak at this point. (will spray the bubbles to find any other leaks in a day or two just to check that box....).

It looks like the next thing to do is to get another one piece Superior Seal and try it again....but I will do that after running the ashless oil for awhile and see if things change.

Thanks,
Paul
 
BTW - One foot (12") of water is only 0.5 PSI - - 3 psi is 72" of water. Maybe you had a missing decimal. It happens :D

If it is holding 12" over night, is it still weeping/leaking at the front seal?? Even with the negative crankcase pressure (anti-splat)? If so, something is off , like too much oil or not enough drainage. Certainly replace the seal again as a first step, but also check the surface finish on the crank.
 
Well this ain?t Lycoming appproved, but you can find seals with two kinds of springs installed inside the lip. One has hooks, the other ?screws? together, ie one end is formed into a point so it will screw into the other female end. If you can find the screw type, it?s easy to cut a few turns of the female end off to shorten the spring and apply a bit more pressure on your .010? crank. I?ve done this once with success on a .010? crank. I offer it only as a possible option that may or may not be a good idea.
You will also find not all springs are the same diameter. I?m not sure there is really a difference in applied pressure one to another.
Good luck
Tim Andres
 
If you have a chronic nose seal weep that leaks between the seal and the shaft a good remedy is to helix the shaft per CM sb M74-6. Its not a Lycoming SB but the theory works well on any engine. The helixing actually makes a pump the moves the oil away from the seal lip. And a note...when you do it don't be afraid to really use a lot of pressure on the abrasive. When you are done helixing, the shaft should look really, really scratched up. I know many will say that the shaft should be polished there, or the seal will wear out. But this works and it works well permanently, seal lip wear is not an issue. Done it on many, many Lycoming shafts with great success. Also, have had the best luck using the Lycoming service replacement seal, that is a split one and doesn't have an installer installed seal spring. The leaf spring that supplies lip pressure is molded into the seal.
Good Luck,
Mahlon
 
If you have a chronic nose seal weep that leaks between the seal and the shaft a good remedy is to helix the shaft per CM sb M74-6. Its not a Lycoming SB but the theory works well on any engine. The helixing actually makes a pump the moves the oil away from the seal lip. And a note...when you do it don't be afraid to really use a lot of pressure on the abrasive.
Good Luck,
Mahlon

Thanks for posting, Mahlon, that is something I was thinking as it is done regularly on cranks when they can be accessed. The "screw" effect breaks the hydrodynamic lifting and pushes surface film back to the crankcase. It is very effective.
 
Thanks Mahlon! I will defiantly do the procedure as outlined in the Continental bulletin you shared.

By the way, your engine ground run in procedures you sent me years ago worked perfect...had no issues with the engine break... Thanks for your advice and input.

Thanks,
Paul
 
Follow the Lycoming SB to the letter when replacing the seal. I prefer the silicone glue verses the contact cement (just personal preference). Clean very well inside the cavity .... feel for any burrs (the best you can) on the crank. I can't recall for sure, but it seems to me that Lycoming might make a seal for an undersized crank....or maybe it was a machined larger case bore. You might want to call Lycoming and ask. Sure seems like you have changed far too many seals...so something isn't quite right. As others have suggested, maybe it is coming from somewhere else. However, if you are seeing it inside the ring gear, the nose seal is the first place I would suspect. Maybe time to look elsewhere. Clean the engine well and use some of the dye penetrant developing spray to coat the area white. Run briefly and look for the leak.

There was an article in Kitplanes a while back about mounting a pressure gauge on the oil dip stick to measure crankcase pressure when running the engine. If you really believe you have blow by issues, you could consider doing that. Compression checks and oil turning black quickly have been the clues Ive used in the past. Boroscoping can sometimes show clues as well (scored cylinders, glazing, etc.). My engine has some glazing and blow by now (o-360). Compressions in the low 70's (which isn't terrible). Oil consumption 1 quart in 3-4 hours and oil turns dark quickly. Planning a top overhaul in December. Replaced my nose seal last year and it is still holding fine.
 
Nose seal

Well this ain?t Lycoming appproved, but you can find seals with two kinds of springs installed inside the lip. One has hooks, the other ?screws? together, ie one end is formed into a point so it will screw into the other female end. If you can find the screw type, it?s easy to cut a few turns of the female end off to shorten the spring and apply a bit more pressure on your .010? crank. I?ve done this once with success on a .010? crank. I offer it only as a possible option that may or may not be a good idea.
You will also find not all springs are the same diameter. I?m not sure there is really a difference in applied pressure one to another.
Good luck
Tim Andres

I had the nose seal blow completely out on my rebuilt O-360 after a short startup ground run. Followed the Lycoming install procedure on a new one piece seal. This one started leaking after about 35 hrs. On the advice of our local engine guru we installed a new seal with the screw together spring. We also removed the Vans supplied 1/2" hard vent pipe and replaced it with a 5/8" ID rubber hose matching the vent fitting size. Still holding fine after 170 hrs. Not sure what the solution was or if it was just 3rd time lucky but our suspicion was the 1/2" pipe was restricting the breathing on the unbroken in rebuild increasing CC pressure....FWIW

Al
 
Update on Crankshaft Oil Seal leak

Hi everyone,

Finally we had some decent weather and I was able to test the plane for about 2 hrs after doing the Helix sanding on the crankshaft that Mahon suggested....I no longer have visible signs of oil leaking on the cowl any longer at this point. So this definitely has worked significantly.

When I did the helix sanding (see Mahons post with the Continental instructions) I didn't yet have a new seal, so I took the existing seal off (it is a sold stretch seal, and getting it off in one piece was sort of tricky), and I just put it back on as it looked ok.

So for everyone out there with a similar issue of oil leaking around the seal and the crankshaft, I would certainly recommend to do the helix sanding when you change out the seal.

Thanks everyone for your input and comments.
 
Mahlon

Another thank you to Mahlon for ground run procedures as well a early break in flight procedures. I had to do all that in 100 degree plus temps and everything worked flawlessly. Oil consumption is so low its almost scary.
 
Update on the Crankshaft leak - I have new seals I don't need now

Hello Everyone - quick update.

The other week I had the chance to take the prop of the RV7A, and do a good visual inspection around the outside of the crankshaft seal....it was bone dry (other than the little bit of grease I used when installing the seal that was still on the shaft).

Sanding in the Helix per the Continental SB certainly solved the issue. Now I have couple of extra new unopened seals, which I don't expect to use anytime soon....so if anyone wants to donate $18 to the Vans Airforce site let me know and I will send you a seal via US mail. I have the Superior Brand one piece seals for an O360.

Thanks,
Paul
 
I?ll take it and donate $25.00!
I would like to talk to you about how you fixed your issue..


5 Krueger Hill Road
Pittstown NJ, 08867
 
Got the Seal.

Hi Adam,
I take it that you received the seal a while back...if not let me know and i can see if USPS can track it down.... sent you a PM.
 
Back
Top