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Valve cover gasket

Ron B.

Well Known Member
I have the silicone gaskets on my IO-390 and thought I could, after a while get them all to stop weeping. I have three cylinders dry but one is getting the best of me. I remove them, clean with a dampened cloth with brake cleaner and let dry. Clean and dry both the head and cover and reinstall. The weeping seems to occur around the bottom bolts and probably the center bottom one , with the longer bolt for the Adel clamp to secure the Ign. leads. This last time I added high temp. silicone around the center bolt, but it appears to still be weeping. I don't feel I'm over tightening the bolts, I was torqueing them to specs. , but I've been trying to fix them with the lower cowl on lately and doing them by hand, maybe that's the problem but I highly doubt it.
Any recommendations would be appreciated.
 
Leak Source

I have the silicone gaskets on my IO-390 and thought I could, after a while get them all to stop weeping. I have three cylinders dry but one is getting the best of me. I remove them, clean with a dampened cloth with brake cleaner and let dry. Clean and dry both the head and cover and reinstall. The weeping seems to occur around the bottom bolts and probably the center bottom one , with the longer bolt for the Adel clamp to secure the Ign. leads. This last time I added high temp. silicone around the center bolt, but it appears to still be weeping. I don't feel I'm over tightening the bolts, I was torqueing them to specs. , but I've been trying to fix them with the lower cowl on lately and doing them by hand, maybe that's the problem but I highly doubt it.
Any recommendations would be appreciated.

Are you absolutely certain that the weeping is coming from the valve cover? There are several other places in the vicinity that can leak such as the rocker shaft covers, push rod tubes, and oil return tube fitting.

Skylor
 
I took a mirror and the bottom of the gasket is dry. The oil appears on the bottom of the valve cover right in the recess where the bolts are. It then drips down onto the ign. leads. If the leak was from the sources you mention the bottom of the gasket should be wet?
 
Make sure the flanges on the covers are flat. Place them on a known flat surface like your back riveting plate and make sure they are not deformed at the screw hole.
Silicon gaskets require very little torque. I use a large standard screw driver held with thumb and two fingers, (not in the palm of my hand) as anything more agressive over tightens them. At CI, it isn't unusual for a few screws to take a bit, maybe an 1/8 turn or less.
 
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Make sure the flanges on the covers are flat. Place them on a known flat surface like your back riveting plate and make sure they are not deformed at the screw hole.
Silicon gaskets require very little torque. I use a large standard screw driver held with thumb and two fingers, (not in the palm of my hand) as anything more agressive over tightens them. At CI, it isn't unusual for a few screws to take a bit, maybe an 1/8 turn or less.

I took a close look for this but did not place the cover on a flat surface to make sure. Thanks , I will do that next try.
Ron
 
As JonJay said, make sure the cover flanges are flat. Mine weren't so I put them on a work bench and beat on them with a brass drift and a hammer to flatten them. I also turned the covers over with just the bosses around the holes on the bench, and gave them a good whack with a ball hammer to flatten them as well.

The torquing is critical. Too little and they won't seal and too much and they will squeeze out. The instructions say 25 in. lb. originally, then after running the engine, retorque to 20 in. lbs. I found that after the initial torque, I had to wait an hour and retorque them to 25 in. lb. Then I checked the torque after running the engine and it was still 25 in.lb.

No leaks this time (wish me luck).
 
I know this answer won't be popular, get rid of the silicone gaskets and use cork with contact cement. Use the gaskets that come with the cylinders. They know what works. Do not use silicone sealer on the cork, the gasket will split. Do not over tighten. Make sure the valve cover and bolt holes are straight. Lightly hammer the holes flat or a little proud toward the bolt head side holding the edge of the valve cover on a solid bench if they're sunk in. Set them on a flat surface and look for gaps. A very slight gap under the bolt hole is desirable for pressure between the holes. I have put together quite a few engines and the cork gaskets work great! They will not weep if the cover is straight. Silicone almost always will from what I've seen.
 
I know this answer won't be popular, get rid of the silicone gaskets and use cork with contact cement. Use the gaskets that come with the cylinders. They know what works. Do not use silicone sealer on the cork, the gasket will split. Do not over tighten. Make sure the valve cover and bolt holes are straight. Lightly hammer the holes flat or a little proud toward the bolt head side holding the edge of the valve cover on a solid bench if they're sunk in. Set them on a flat surface and look for gaps. A very slight gap under the bolt hole is desirable for pressure between the holes. I have put together quite a few engines and the cork gaskets work great! They will not weep if the cover is straight. Silicone almost always will from what I've seen.

I have silicon gaskets in this application and you couldn't pay me enough to go to back to cork. Not a single weep in 450 hours and I have been able to take them on and off several times.

The manufacturer spec'ed cork because it was cheap and available in 1950. In the 50's all engine valve cover gaskets were cork. Other than lycoming and possibly Continental, I cannot think of a single engine manufacturer that still uses it and the reason is that they don't hold up over time and leak. Lycoming does not choose to avoid silicone because they don't work. It is more related to their resistance to change; Probably regulatory induced, as well as cost.

Larry
 
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I have silicon gaskets in this application and you couldn't pay me enough to go to back to cork. Not a single weep in 450 hours and I have been able to take them on and off several times.

The manufacturer spec'ed cork because it was cheap and available in 1950. In the 50's all engine valve cover gaskets were cork. Other than lycoming and possibly Continental, I cannot think of a single engine manufacturer that still uses it and the reason is that they don't hold up over time and leak. Lycoming does not choose to avoid silicone because they don't work. It is more related to their resistance to change; Probably regulatory induced, as well as cost.

Larry

Right the cork are cheap and I have had very good results with cork. Possibly your covers weren't quite straight or they were over tightened? My engines seldom leak anywhere. Even 0-300's. Just stating what has personally proven to work for me over many years. After re-reading my first post maybe I was too direct or critical. Guess I write like the manuals I read daily...Do and do not!:=))
 
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Leaking Valve Cover Gasket

Hi Ron,

I too fought this same problem with IO-390. I found three things after replacing three silicone gaskets that failed to stop leaks.

1). Not all silicone gaskets behave the same. What mfg of gasket are you using? I had success with the Lycoming Factory gasket $$ or Real Gasket https://realgaskets.com/product-category/aviation/aviation-opposed/lycoming/ or ACS P/N 05-11183.

2). Additionally, I found using a torque wrench designed for screws worked much better (more consistent) than a traditional torque wrench. https://www.amazon.com/gp/product/B000RZ1D86/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

3). Lastly, follow these directions exactly https://realgaskets.com/wp-content/uploads/2017/03/RG-67193-SP.pdf

Hope this works,
Rocky
 
I have certainly improved the weeping. There was not any indication of oil on the cowl this time. What I'm seeing on the cover could be residue from oil on the ign. wires, hard to clean the oil there. I'll keep monitoring.
Thanks all
 
brake cleaner

I don't know if it's right or wrong, but I use non-chlorinated brake cleaner to clean the oil residue off the engine.
 
Back in the day with sheet metal warped valve covers and cork, one way that works, straighten flange, use a bead of ultra Black RTV on one side of the gasket and place on valve cover, turn face down on a flat surface with a weight on top and let cure overnight, now the gasket will not move around and fit the flat machined surface of the head. I have the silicone gaskets on my setup and no leaks or weeps. Dry.
 
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