340 Exhaust Manifold Condition

[Paul97]

Just sand blasted my original 1970 340 Exhaust Manifolds today.  The heat riser was poorly welded up at some point.  Is this common?  I see two options for repair:

1. Grind out the garbage welding and seal weld the heat riser shaft bores closed.  Don't install a new riser.
2. Build up the pad and re-bore for the heat riser shaft and pin.  Install a new heat riser kit.

I'm going for a stock looking restoration, but I think I may need to let the heat riser go given the heavy pitting on the Manifold in that area.  Is there any real reason to keep the heat riser other than originality?

I've welded castings before for work, so I'm not that worried about welding on them as required.

I think much of the surface area on the manifolds looks decent.  Some of it seems really pitted to me though.  Am I better off just buying the reproductions?  This is the first set of really old manifolds I've seen, so would appreciate any input.  I was planning on having them refinished with cerakote powder (or something similar).  I don't want to spend a bunch of money on them and have them turn out not looking good installed.  Would like to know what you all think.

[Dakota]

I can't tell for sure, but it looks like the circular plate that's normally mounted on the shaft of the heat riser is already gone on yours.  If that's the case, leaving the shaft in place won't make a difference unless those welds leak.   The one rebuild kit I came across for the heat riser mechanism is pretty pricey - almost $400.  The plate restricts flow to push hot gases back through the intake manifold to speed warming up the engine.   Since most of us don't/won't drive these cars during cold weather because of road salt, you probably won't miss having it from a performance standpoint.  Lastly, if you're going to use one, they require some routine lubrication to keep moving freely.  Basically, my 2 cents is to go without it.

The set of manifolds I have are pitted just a little less than yours.   I think the main things to be concerned with are a lack of cracks and being comfortable that the sealing surface is in decent shape.   From what I've read, the true stock arrangement doesn't involve the use of gaskets between the engine and the manifold other than the heat shield on one side (I think it's the passenger side).

[Paul97]

Dakota,

The circular plate (actually everything but the shaft) is long gone.  I'd have to source all of it.  And I certainly won't drive in the cold weather.

[Cuda Cody]

I like stock and I even prefer not to have the heat riser. 

[Dakota]

This is the rebuild kit for the 1968-70 heat riser.   It's $389.   

http://www.bradsnosmopar.com/nosmo19340ex.html

There are a couple of others kits available (some less expensive) from the same source for other variations of the heat riser.

[Paul97]

Thanks Cody.   It will certainly be easier to do without it.  What do you think of the pitting?

[Chryco Psycho]

The heat riser just forces heat through the intake to warm the carb , most of these cars are not daily drivers or are driven in winter so I alway block the heat crossover to keep the carb cooler so IMO there is no reason the have the heat riser plate , you can put a pin & spring there to look original from the outside easily though . 
Do not use exhaust gaskets , they will cause leaks , I just use a thin layer of Copper silicone to seal between the head & manifold so the pitting will be no issue same with the flange gasket , I use a thin layer of silicone there too  , the pitting around the heat riser area can be ground down a little to clean it up , You could have the flange milled off 1/8" or so to clean it up , the pitting is not bad enough to warrant spending for new IMO 

ceramic coating is definatly an option too

[RUNCHARGER]

I don't think the pitting will look bad in the car. The missing heat riser bits are hard to spot when on the car so I don't know if I would spend the $389 either. One thing I remember from when the cars were relatively new is that most 340's seemed to have a rattling heat riser valve. You could usually hear them from a half block away. O course maybe that was just a feature to scare the other cars away.

[6bblgt]

the top of the RH manifold looks pretty good, the pits wouldn't bother me - what's the top of the LH one look like?

& those appear to be dated:
10058 - 10/05/68
10288 - 10/28/68

& probably originated on an early '69 A-body w/340 - if that affects your decision

[1 Wild R/T]

Thing I'd be most concerned with is sealing the flange to the head pipe.... Might want to try dressing that on a belt sander...

[fc7cuda]

For a driver, weld up the holes.   

Upper level judging or if it's important to you, then you'll have to install the kit or at least enough of it to appear complete.

Good luck 

[AAR#2]

I like stock and I even prefer not to have the heat riser. 

I'm with Cody on this one, however because I like stock and want the appearance that all is complete and functional I made a few modifications to accomplish the install.

Since the only thing that hold these in is the weld to the butterfly you need to have a way to retain the counterbalance shaft both inboard and outboard, this can be accomplished by machining a small groove on the shaft just inboard of each bushing and retaining the assembly by using a c-clip.

Under normal operation exhaust gas reacts against the butterfly to keep the rotation such that the thermostat is engaged against the pin. Since we have no butterfly all thats needed is to wrap the thermostat spring around the pin. (lust the small reverse bend that engages the pin)

Installing this way looks completely stock, does not restrict, is easily removed if needed (by dropping the pipe and pulling the c-clips) and allows the thermostat to rotate the counterbalance as if everything is installed and operational.

[Topcat]

This is the rebuild kit for the 1968-70 heat riser.   It's $389.   

http://www.bradsnosmopar.com/nosmo19340ex.html

There are a couple of others kits available (some less expensive) from the same source for other variations of the heat riser.

Caveat Emptor with this buyer.

He has been mis-leading in the past.   

[71GranCoupe]

Here is my  on the manifolds. From what the pictures show, they are quite pitted. With that in mind, I would clean them up and put them back on the car as they sit after cleaning the welded area up. Use the money you were thinking about using for the heat riser set up and start looking for a really nice set of replacement manifolds. Then sell the pitted ones. 

[RUNCHARGER]

Best idea yet.