The International Cessna^® 170 Association

This is "Oil Leak-Pokey" with another request for suggestions. After correcting the problem with my leaking valve push rod tubes I have 2 valve covers that just won't stop dripping I have replaced the gaskets with new ones (Real Gaskets) and still DRIP-DRIP-DRIP I have torqued the screws as much as I think I should, but same ole drips. Now I am wondering---should I try putting some Aviation Permatex on the Real Gaskets or should I pull off the Real Gaskets on those 2 cylinders and go back to the old style gaskets and Permatex them in. I know the Permatex is a bugger to clean up when that becomes necessary, but I am getting tired of dripping oil all in my cowling and onto the ramp everytime I stop. Am I missing something in how I am trying to correct this problem

I chased a similar leak about a year ago. Turned out to be a small crack in the valve cover itself...

Are you sure its not the top end of the pushrod tube?

Frank,

The problem with the REAL gaskets is if you tighten them to much they leak. If you don't tighten them enough they leak. They seem like a good idea but but maybe they aren't. This is not to say lots of people haven't been successful using them.

One thing to check with the valve covers no matter what gaskets you use is the holes the screws go through. After tightening the covers so many times the valve cover is no longer flat around the holes but pushed in toward the cylinder head surface. If this happens it basically keeps the valve cover from sealing all round the edge. I take a small ball peen hammer and flatten the valve cover around the holes when I see this happening.

I've come to the conclusion that the best method for me to seal valve covers is to use the cheap regular gaskets with a small bead of your favorite automotive silicone gasket maker on each side of the gasket. This glues the valve covers on requiring removal with a rubber mallet but they won't leak. And since I'm using the silicone gasket maker with them I can often reuse them over and over.

If you use a sealer with the REAL gaskets, I'll bet you end up ripping them, destroying them when you do remove the valve cover and that's a lot of money.

And like Karl said, are you SURE the tubes aren't leaking. BTW check carefully. Several of my push rod tubes actually had holes rotted through them that you couldn't see because it was on the top in the area closest to the cooling fins.

I appreciate the suggestions and will check the valve covers carefully when I remove them. I suspect I will use the old style gaskets on these two due to the hassel of removing the baffeling, etc. to get the covers off and if I can stop the leaks there normally isn't any need to remove them. Bruce, are you using just silicone in a tube like one would get at Home Depot, Lowe's, Wal Mart or other hardware outlets?

Frank

Frank, I use a silicone gasket maker from the automotive industry specifically made for this type of seal. You may be able to find it at Lowes or Home Depot in the automotive section but it is not the same silicone sealant you would use in your kitchen or bath. You can find it at WalMart and every other automotive department or store I can think of.

Normally you would not use a gasket with this stuff but you can. There are several manufacturers, Permatex is one, and there is regular and high temperature as well as stuff that is sensor safe.

For this purpose you don't need high temperature but it won't hurt and you don't have any sensitive engine sensors to worry about. I usually pick the color I like more than anything. BTW I use a bead of the high temperature stuff directly on the no blow exhaust gaskets to help them seal against the cylinder head. Don't know it this helps but it hasn't hurt.

I've used all of the following products at one time or another.

I used automotive high temp silicon for exhaust gaskets on our towmotor years ago and it hasn't leaked since. I lightly snugged the bolts for overnight until cured and then retightened them.

John

Be careful using RTV. You don't want it getting in the oil and blocking oil passages. Although I've never used it, others have sworn by Yamabond #4. It's available at your local Yamaha dealer.

An excess of anything getting in the wrong place can cause problems. The key is it doesn't take much of the sealer specailly with a gasket. The thinest of a bead maybe a 1/8" is all that is required. That is difficult to do so I usually spread a thin coat with my fingers.

Thanks to all for the suggestions. I have some of the Red stuff and have used it previously in vrs places so I may use a little on the old style gaskets if I have to resort to using them.

Be certain that whatever you use,... the product states it is intended for use as gasket sealer. Not all RTV (Room Temperature Vulcanizing) sealers can withstand oil. Don't use too much. Excessive RTV will migrate to places you don't want it.
Clean the surfaces before application. Use alcohol, Acetone, or ordinary gasoline to clean and dry the surfaces before applying the RTV.
The surface of the cover must be flat/true. Excessive tightening of the screws deforms the covers and causes leaks. (I like the "silicone" rubber gaskets but they will leak if tightened excessively as they squeeze out of shape. I'll bet your covers are deformed or your gaskets were overtightened.)

I have a new, never installed, still in original packaging, Millenium cover I'll never use if you need one. (Doesn't look original.)

I know a guy that had his A&P license taken away for a while, for useing that kind of stuff.

Hylomar is an approved RTV sealant, but it's expensive. Check with Tex Air parts at FTW, Frank.

Hey Frank,

Hylomar Is the best stuff I have ever used to seal gaskets. I have a tube. Let me know when you are going to be around, and I will bring it to you.

Patrick
170A N1410d

George, I'm curious were you found Hylomar as an approved sealant. It's not listed in SIL-99-2 the bible of Oils, lubricatants and sealants from TCM.