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Posted by D Sherman [72.47.9.228] on Thursday, June 17, 2010 at 02:15:54 :
In Reply to: Exhaust Manifold Installation Help Needed posted by Chris [68.60.186.165] on Wednesday, June 16, 2010 at 16:14:23 :
I can't help with the 318 specifics and the nuts. If brass nuts were stock, that's what to use. If there are washers, use the heavy, hardened ones, not soft "hardware store" washers.
On the sealer, though, I've used various things. If the block and manifold are good and smooth, no extra sealer is needed. If they're badly pitted, I've used red or copper (hi-temp) RTV (silicone) and it's held up okay. It's easy enough to have the manifold milled, but the block is another story, which is the reason for using silicone. Silicone will not survive direct exposure to exhaust gas and pressure, and will not work as a gasket by itself, though I once had some success on a small engine using ordinary asbestos paper saturated on both sides with red RTV. RTV will fill small pits in the metal, though, and since the exhaust gas doesn't impinge on it directly, but has to squeeze through a few thou gap to get to it, it seems to hold up fine. I've seen lots of commercial installations with red RTV squeezed out around the manifolds, so it must be common practice.
As far as sealing the bolts into the water jacket, I've always used plumbers TFE paste (brush-on white goop with teflon in it) and it's held up fine. Somewhere I read not to use that, but I'm not sure why, since it says on the label that it's rated for water, oil, gasoline, and glycol up to well above radiator temperature. I wonder what they used in the old days? White lead and linseed oil?