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  #1  
Old 09-30-2018, 01:14 PM
Triumph1974 Triumph1974 is offline
 
Join Date: Feb 2008
Location: Richmond VA
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Default Causes of Crankshaft Seal Leaking a little oil

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
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  #2  
Old 09-30-2018, 01:34 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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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
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Last edited by lr172 : 09-30-2018 at 01:55 PM.
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  #3  
Old 09-30-2018, 04:52 PM
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snopercod snopercod is offline
 
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Location: Asheville, NC
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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.
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Old 09-30-2018, 06:16 PM
BillL BillL is offline
 
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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.
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Last edited by BillL : 10-01-2018 at 08:33 PM.
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  #5  
Old 10-01-2018, 08:26 PM
Triumph1974 Triumph1974 is offline
 
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Location: Richmond VA
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Default 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....
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  #6  
Old 10-02-2018, 06:52 AM
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snopercod snopercod is offline
 
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Quote:
Originally Posted by Triumph1974 View Post
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.
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Old 10-02-2018, 08:19 AM
flysrv10 flysrv10 is offline
 
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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.
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  #8  
Old 10-02-2018, 10:00 AM
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bruceh bruceh is offline
 
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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.
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  #9  
Old 10-02-2018, 10:02 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Triumph1974 View Post
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
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  #10  
Old 10-02-2018, 05:54 PM
Ralph Ketter Ralph Ketter is offline
 
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Quote:
Originally Posted by Triumph1974 View Post
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.
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Last edited by Ralph Ketter : 10-03-2018 at 04:19 PM.
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