Questoin about hi-temp silicone sealant for exhaust
I have read here on several occasions that a bead of hi-temp silicone sealant will do as well as or better than gaskets for sealing the gap between our side pipes and the end of the cats/J-pipes/header. I have never heard details about how the sealant should be applied. Here's what I mean specifically.
I used a similar bead of sealant to seal my Canton oil pan to the bottom of the engine some time ago. There, I laid in the sealant bead around the top of the pan, then waited 24-hours for the silicone to setup with the pan free of the block; and only after that did I bolt the pan up tight to establish the seal. I wonder if the sealant application at the side pipe connection needs to be made the same way in order to do the job best. Otherwise, the option is to apply the sealant and immediately smoosh the joint tight with the bolt connections. I would like to know what other builders have done here. It seems like a good idea to pitch the gaskets if the sealant work as well or better.
Rich has it closer. Not sure of the actual recommended time, which may vary a little between products, but go by what it says on the package. Letting it harden for to long could cause a no seal problem as you might end up with small lumps unless you are extremely good at getting a purfectly even bead all the way around. This would be more of a problem on thin things like pans and valve covers but you never know.
MK3#5902 picked up 1/13/07, 88 donor 306 w/b303 EFI purchased 3/31/07,first start and gocart ride 9/20/07 color- Ford Performance White w/ True Blue Metalic stripes. Inspected and registered 7/31/08
The problem w/ letting the silicone dry too much is that it will only be adhered to the one part that it was applied to. It won't be adhered to the second part. So you have a bead that is on one part,that is varying thickness due to normal human hands being what they are, and then it is simply compressed between the parts. This would,it seems to me give you a seal similiar to what you get when one of the parts isn't clean and dry. I can't think of any applications where this would be a good procedure.My experience says that both surfaces must be clean and dry so the silicone will adhere to both.
FFR 5353K,351/400hp,TKO 500, 3-link w/3.31 and Truetrac, Koni DA coilovers front and rear,APE hardtop,Forte front and VPM rear swaybars
I gave up using header gaskets a long time ago; silicone only.
On the J pipes, I would only use silicone between the J pipe and side pipe. But at the header connection, it's designed to use a donut gasket to make allowance for any misalignment. I would use a donut gasket, but then add silicone at the contact surfaces.
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Dart 427W, Momar 8 Stack EFI, 600'ish hp, TKO, 3.55 TruTrac, Red with Ghost Flames. More fun than should legally be allowed.
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