Exhaust leaking at manifold

[red70vette]

I have a 1970 cpe with a 350/300 original engine. The exhaust was replaced sometime in its history. I have recently noticed an exhaust leak at the passenger side heat riser.

I have replaced the gasket between the heat riser and the manifold but there is still an exhaust leak. The leak appears to be between the heat riser and the exhaust pipe. There is a donut shaped metal extension that fits between the pipe and the heat riser. Is there a gasket or some type of packing that goes around it. I have tightened the manifold bolts but it still leaks. I don't want to tighten them too much as they are the originals and are somewhat rusted. The last thing I want to do is break them off and have to tap new bolts in.

The heat from the leak has metled one of the A/C hoses. It even went so far as to start a fire as the hose burned. Anyone experience this? Any solutions?

 

[JrdnsEdu]

Is the flap on the heat riser stuck in the closed position? Mine was and after welding it open for good, my leak is gone for good.

 

[JohnZ]

Yes, there's a donut-shaped composite gasket or "packing" that goes between the exhaust pipe flange and the heat riser valve, and the sleeve/extension that fits into the top of the exhaust pipe goes through the hole in the "donut" to support its inside diameter. It's shown in UPC 8 of your assembly manual, and any auto parts store has them. Make sure the weight on the heat riser valve moves freely through 90 degrees and snaps back to the closed position (check when cold).

 

[red70vette]

I have since wired the heat risen in the open position but it appears that I am missing the extinsion that goes on the inside of the packing donut. I will check with local auto parts stores to try to find it.

Thanks for the replies.

 

[JohnZ]

The little extension is essential - without it, the I.D. of the "packing" has no support (and its O.D. is being forced inward by the chamfer on the heat riser and the flange on the exhaust pipe), so the "packing" fractures, then disintegrates and disappears. Many folks don't understand the function of the extension and throw it away, and later have an exhaust leak. Most auto parts stores have them in different sizes.