Any suggestions on how to get these valve covers to stop leaking? I've tried two sets of used covers, both of which appear to have straight sealing surfaces, but they just keep leaking. Any recommendations on gaskets and gasket sealers? Thanks.

On some Poly's over the years the valve covers get warped. The area where the bolts go through bends down so that bolt heads bottom again covers, and cover bottoms against rocker pedestal before adequate pressure against gasket. Straighteneing the covers against a flat surface at bolts helps.

Also FelPro came up with a much better rubber coated steel gasket that seals better than the old cork type.

Also there's oil drainback holes at lower outside corners of heads, front & rear corners. A brass gun cleaning brush about .38 caliber does a good job of opening them up. Otherwise oil can pool in the head recesses causing leaks and allowing oil to drip past valve guides seals, causing smoke at startup.

Use the rubber gaskets, they should stop the leaks.
Be sure that the mating surfaces are cleaned of all oil and residue before you seal them up.

You may also want to check the pcv valve/hose or breather as not to be plugged and causing back pressure in engine forcing oil out.....pat

i would definatly check where the bolts go thru, there is a 90% chance they have been over tightened in the past. and like mentioned above, they will bottom out before they apply pressure to the gasket. i take it a step furthur. use the rubber gaskets for sure, but i coat both sides with copper coat spray sealer. spray one side of the gasket, give it a few minutes then install on the cover. be sure its going in the little holders properly or the gasket can slip out and cause leaks when tightened. then spray the bottom side of the gasket, give it a couple minutes and install. this in effect glues the gasket to both sealing surfaces, be sure everything is clean and oil free before you start and you should seal up and not leak. i wouldnt use rtv, before it cures its slippery and will usually aid the gasket in slipping out of place before it cures.

2 RTV tricks:
1. Coat the cover with RTV, insert the gasket, let set a couple days til fully cured. Now it stays nicely in the cover, right where it is supposed to be.
2. Coat both sides of the gasket, install the cover, tighten the bolts finger tight, let set awhile til RTV is at least 1/2 cured (8 hrs +/-), then torque the bolts. Gasket will stay in place and seal up nicely.

who wants to wait 8 hours for messy rtv???

That's the beauty of it, if u wait, it aint messy!
Do u know how to use denatured alcohol for smoothing silicone w/o getting it on u or anything else, as well as removing all the excess?

carefully!!

I have a reaction to alchohol, haha. Terry I wanna know,,,,, Also why use a gasket at all RTV works on la engines as long as you shoot the surfaces with either

Apply silicone to the target, completely. Dont worry about excess or trying to shape it. Just be sure it fills every void u want it too. Using a common squirt bottle with adjustable spray tip, spray the denatured alcohol over everything, the more the better. Be sure it is on all adjacent surfaces and pooling along the silicone. Wet your fingers with it too. Now just finger the joint to cut the silicone to a beautiful, smooth bead, wiping the piles of excess off your finger onto a paper towel. Spray again after the first wipe to keep a film of alcohol on the silicone.
The silicone will not stick to you, or the adjacent surfaces and excess overfill will come off to give a perfect bead.
No fuss, no mess, FAST and CLEAN!
The only caution is that alcohol will dissolve many paints, so against a painted wall, u gotta move fast. I dont know how it reacts with engine paint.
George, your tongue will have a helluva reaction with this kind of alcohol, and your stomach too if it gets that far

Thanks

Great tech tips, Terry!

When I do those gaskets I prefer to only silicone the valve cover side. The head surface is machined and cannot warp but the valve cover can bend or flex & ruin a good seal. In my past experience just attending to the valve cover sealing with silicone results in a valve cover that doesn't leak but can be easily removed, no fuss or bother. That's important on the solid lifter engines to allow periodic valve adjustments.