Chevy SB exhaust leak.

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Feb 24, 2009
Abingdon VA
I have a 86 K10 with a 305 SBC. I have a leak around the heat riser on the pass. side exhaust manifold. I was told by the dealer that its not suppose to have a gasket and auto parts stores don't list one either. My question is what is the best way to get this thing to seal up. I was thinking about removing the manifold and wire brushing the mating services to see if that would work. Any one have any ideals.
Originally Posted By: mechjames
Fel-Pro MS9275B is the gaskets for your manifolds. $5 bucks online from rockauto.
Yeah I have those the part im asking about is where the heat riser mounts to the the manifold its self.
Originally Posted By: Chris142
Any muffler shop will have a gasket to put in there.It's a common size.While you have the heat riser off take it to a machine shop to be surfaced.
Alright! Just have the heat riser surfaced?
Originally Posted By: RH+G
Usually when u have a leak its cause the heat riser is stuck closed
The riser linkage moves freely. But the vacuum line has been unhooked. I wonder if its default is open or shut?
This could also simply be that the bolts are loose or broken. You could try tightening them, but be prepared for breakage in old and rusted stuff.
IIRC its closed by default and opens through a thermal vacuum switch. As the engine warms the vacuum switch opens and allows vacuum to the heat riser actuator valve. A closed heat riser can leak slightly, try opening it and see if it quietens down.
Make the gasket out of copper sheet. I did that for the heat riser coming out of the manifold in my car, as well as exhaust gaskets for many cars and lawnmowers. Take a short length of copper tube, slit it lengthwise, open it up and pound it flat. Use a metal saw and coping saw to cut what you need. Finish by filing. Of course the mating surfaces must be flat.
If the heat riser leaks exhaust I assume it is warped or corroded. And if it is inoperative I'd probably just replace it with a new one. The heat riser should improve cold running warmup and drivability and the fuel savings would probably pay for the valve in a short period of time.
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