Are you certain it is the china rail leaking? When installing the machined intake, verify the fit before torquing with a feeler gauge. Any gap should be identical top and bottom. The coolant can still seal because of the printed sealant or embossing, but still seep out just above the head gasket. Could the head gasket be leaking slightly in that thin area by the pushrods?
Cat had a green/yellow gasket adhesive similar to the yellow weatherstrip adhesive. Brush on the gaskt and the metal and let sit for a couple of minutes. You better get the positioning correct because at contact it stuck like **** to a diaper. Used a lot on final drive covers and oil pans. This was before the 3M buffing disks. What a beggar to get clean with a scraper. Final drive covers had a few dowels and required puller bolts to get them off.
I was referring to contact cements or adhesives. RTVs are a piece of cake. Use contact cement on both sides of an Al intake manifold and you may damage crap out of it trying to get it off.
Gotta go into Sherlock Holmes mode. Any leak will leave a trace. That will be a thin wet track on the silicone or a gasket surface. That part of a gasket or the silicone will not stick well. Careful disassembly will let it show.
Clean the China wall well and make sure the locating pins are removed. Aluminum intakes don't have holes for the pins.
You should always dry fit the intake to make sure it fits properly before you add sealer. The gap on the China wall will let you know how much sealer you may need.
Low stress area, so I would JB Weld it. Cleaning the base metal is the important step. DV shows building up port floors with epoxy. He drills a few holes right through and flares it so there is a positive lock on top of the chemical bond. Sure do not want that breaking loose and heading through the intake valve. That area has no fluctuating air flows to dislodge it, just vibrations and expansion and contraction. For what is involved the epoxy will function well as long as the base metal is clean. When you clean it, be ready to apply the epoxy right away. Aluminium gets surface oxidation virtually immediately that restricts adhesion. Again, a low stress area so not as much a problem.
I feel ya.. china rail seeping oil is my bane so I use Right Stuff. Usually once you get one corner moving it'll release. Razer blade followed by a wire brush usually does a good cleanup. Ultra black will likely be fine as well.. just be sure to measure the gap and get a good size bead in there. If you don't see a bit squish out all the way around you likely did not use enough. After i dropped the manifold on I forced a bit more into the crack at the front as I did not get the amount of "squish" I wanted.
I feel ya.. china rail seeping oil is my bane so I use Right Stuff. Usually once you get one corner moving it'll release. Razer blade followed by a wire brush usually does a good cleanup. Ultra black will likely be fine as well.. just be sure to measure the gap and get a good size bead in there. If you don't see a bit squish out all the way around you likely did not use enough. After i dropped the manifold on I forced a bit more into the crack at the front as I did not get the amount of "squish" I wanted.
GL!
West System to clean and it treats the surface so it can not oxidize. Then the epoxy can adhere.
