Rocker cover gaskets
 

Switching from old cork to new silicone rocker gaskets. Lyc service letter says torque to 35 in-lb instead of the usual 50. Is that sufficient to preload the screws, or does retention depend only on the lock washers? Main question is whether it is advisable (or not) to use a bit of Loctite. Any experienced, knowledgeable views from the field?

The instructions that come with the R.E.A.L silicone gaskets say to initially torque to 25 in.lb., run the engine, then re-torque to 20 in.lb. Originally, I had the same concern as you about the screws coming loose, so I tried some blue Loctite. I wouldn't do it again, though, because it prevents re-checking the torque during the annual condition inspection. Just be sure to use the Lycoming pan-head screws with the star lockwasher and you'll be OK. The one thing you don't want to do is over-torque those screws, That pinches the gasket and guarantees a leak. (Ask me how I know)

Also, before installing the rocker covers, be sure the surfaces are flat. Mine weren't, so I placed them face down on a heavy wooden bench and beat the flanges flat with a hammer and a piece of wood.

So here is some of my thoughts as to the reasons -
You only need enough torque to ensure while the engine is cold that there is some pre-load on the screws and thus a good seal
When the CHT increase, the silicone gasket heats up and expands which will increase the effective torque and increase the sealing
If you were to over tighten / over compress the seal when its heats up and expands its gotta go somewhere - in extreme cases it could "extrude" itself and start to leak or distort the cover.

I have seen applications where O ring grooves have not been tolerance correctly and the O ring has blown the two interfacing components apart when heated.

Also never underestimate the force silicone in a confined space can create when it is heated up.....

I have gravitated back to cork gaskets. Properly installed they do a great job. Cork swells on contact with oil in a self-sealing mode. And you can apply the full torque to the fasteners. How many times have you seen over-tightened covers with silicon gaskets migrating out? Or that guy in the shop with a screwdriver who can't keep himself from snugging the valve cover screws every time he gets near one. Cork cures most of these digressions. If silicon were truly "all that" you would think Lycoming, Lycon, CMI and other manufacturers would be using it. They don't. Their objective is to put out the best product possible. They all use good old cork.

Jim

One point that took me a while to grasp was the gaskets need to be dry as do the heads when you install. No oil what so ever. If a drop of oil seeps down before you torque the screws it will leak.

oil on gasket
 

Didn't know this - thanks for the tip.

Gaskets
 

I hate those red thick squishy gaskets.

If you want a nice gasket send an email to Guy Ginbey n77gb@msn.com

He will send you a reinforced rubber gasket that won't squish out when you tighten the screws. Nicest gasket I've found.

Or buy the new SDS covers that use an O-ring and never have to worry about all that squishy stuff.

I replace leaking cork gaskets on a regular basis, never had to replace a silicone one. I've had the same silcone gaskets on my own aircraft for over 12 years with 0 leaks.

If you ask me manacturers continue to use cork because they are cheaper.

Same experience as Walt.

All of the Van's demonstrator aircraft have silicone gaskets (the same ones available through the accessories catalog). Some of them have been installed for 18+ years

They last forever and will not leak if installed properly. All contact surfaces, including the gaskets them selves must be totally clean.
I have found that at first installation when new, the gaskets have an oily film on them that must be removed before installation.