The International Cessna^® 170 Association

George, what type of Hylomar are you talking about. They have 3 products, one is an RTV the other two are not.
http://www.hylomarusa.com/products.htm

Univeral Blue is what was approved for aircraft engines by Rolls Royce and Continental. "Typical applications include water pumps, oil pumps, instrument inspection covers, cylinder heads, oil sumps, intake manifolds, timing case covers, gear box and transmission housings, and as a coating for pre-formed gaskets."

http://www.hylomarusa.com/universal_blue.htm

Their RTV has been used for gaskets for oil sumps and it also does a good job, but not officially "blessed".
http://www.hylomarusa.com/rtv_sealants.htm

It looks like there are several formulations of Universal Blue including several "Aerograde" versions.
http://www.hylomarusa.com/data.htm
It sounds like the "Aerograde Ultra" version is the one used by Rolls Royce.
http://www.hylomar.us/pdfs/MSDS/TDS%20H ... 0Ultra.pdf

if you use the Real gaskets which I believe are silicone construction, then no sealant will really do you much good - nothing much sticks to silicone material. the best for that would probably be Permatex form-a-gasket #2. if you're worried about removing form-a-gasket residue just use carb cleaner, cleans it right up. I use Form-a-gasket on pretty much all of the gaskets when I build up engines, it fills in the pores etc in the metal surfaces left from tool marks, bead blasting, etc. you can also use it on bolt threads where they penetrate an oily area, like some case bolts etc.

a persistent oil leak up in the rocker box area is likely either a tiny hole/crack in something, leaking rocker cover (crack from overused screw holes, wear from rocker shafts, or deformed from overtightening - a bigger problem with the silicone gaskets), or the pushrod tubes. I had good luck sealing a couple of leaking pushrod tubes by using some JB weld on them when I reswedged them.

A small corrosion hole in one and a crack at the screw hole in another of the 6 magnesium pushrod flanges where the pushrods enter the engine case was the culprit causing a substantial oil leak in my O-300B. It took pulling the cylinders to discover it but was an easy fix otherwise.
Unfortunately now we're back to chasing leaky pushrod seals, leaky starter gasket, etc ....
It'll be a happy day when there isn't a bunch of fresh drips every time I pull up and park someplace

If it ain't leaking, it's probably out of oil!
I kind of enjoy wiping the little trail of oil behind the firewall...
Helps me bond with my bird.
Cheers

Fishdoc, sounds like you are "feeling my pain" or vise-versa I guess we don't have to worry about things rusting because from cowling to tailwheel gets lubercation 4 Stripes, I like your attitude. I need to look on all of these challenges with a similiar one Someday I am going to go out to the hangar and have nothing to do except go flying--------aah, I remember those days of long ago Maybe I need to put some Bar's Leak in my sump. That would stop those cottonpicking leaks---------permanently

Just pretend it has a radial.

WHAT I don't have a radial with all the oil leaking out my cowl?

Well coincidently, I have the same problem going on. 4 of my 6 silicone "Real Gaskets" have started to leak to an annoying level. I don't know why as I have not touched the screws to overtighten them. But once these things start to leak, they don't seem to stop. So I have decided to go back to regular old gaskets. I discussed the matter with my engine rebuilder and he said NO to Permatex style RTV. He said to use Hylomar (didn't specify which Hylomar product exactly) or plain old Fuel Lube. Also talked to my regular A&P and he said to use Fuel Lube too. Fuel Lube doesn't so good in this application to me but what do I know? Anyone else use Fuel Lube with any success?

Thanks, Bruce

N3243A wrote: Anyone else use Fuel Lube with any success?

Thanks, Bruce

Yep......

As others suggested, first be sure the rocker box covers are flat. Second, there can be no oil on the rocker box or the covers. They'll not seal and for sure will leak if not dry before installing. Finally, if you decide to go with the "old style" gaskets, try using HondaBond or YamaBond (from your friendly Honda or Yamaha parts dep't.). These seal MUCH better than RTV or its ilk, and can be removed. A thin film is all you'll need.

After repeated attempts at stopping the oil drips on 2 of my valve covers, "I THINK" I may have finally succeeded in fixing them. Sat morning was spent removing them once again and inspecting the Real Gaskets for damage. One had cuts up high which may not have contributed to the leak, but a little work on the valve cover itself and careful replacement of a new gasket (and a trip around the patch) seems to indicate that one is, at least for the most part, fixed. The second one appears that the mechanic (well the wrench turner--ie: ME ) apparently got the gasket upside down in the valve cover and now that I have completed that task, it too seems to have stopped leaking. Engine got a wash down today and now another test flight is needed to confirm if this did the trick. I appreciate all the suggestions and hope I can return the favor at some time.

170C wrote:... the mechanic (well the wrench turner--ie: ME ) apparently got the gasket upside down in the valve cover and now that I have completed that task, it too seems to have stopped leaking. ....

UH-OH, Frank. You didn't also get it INSIDE-OUT .... did you?

Well George, I don't know about INSIDE OUT, but there sure is a difference in wrong side up and down. Its easy to get the gasket incorrectley installed and also easy for it to drop down or be up a bit too much when actually putting the valve cover back on the cylinder