| [GMCnet] Exhaust riser valve [message #120625] |
Sat, 02 April 2011 19:33  |
Richard Brown
Messages: 281
Registered: May 2009
Karma: 1
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If anyone has a riser valve lying around, could you check to see what position the weight is when it's wide open? The manifold is still too hot to work with on mine, but the weight appears to be nearly horizontal(sticking straight back). What I'd mainly like to know is does the bimettalic spring (which is gone) hold the valve closed & once heated allow the weight to open it up or the other way around? I would figure that if the valve was working, removing the spring would allow the weight to hold it wide open. I not try to remove it until it has the chance to soak a bit. I put penetrating oil on the bolts, but it's still hot, so most of it smoked off. If I can see which way is open, then maybe I won't need to take it off if I don't have to.
Richard & Carol Brown
1974 Eleganza SE
"DILLIGAF"
Lindale, Tx. 75771
903-881-0192
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Richard & Carol Brown
1974 Eleganza SE
1174 Hickory Hills Dr.
Murchison, TX. 75778
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| Re: [GMCnet] Exhaust riser valve [message #120653 is a reply to message #120625] |
Sun, 03 April 2011 04:28  |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Richard Brown wrote on Sat, 02 April 2011 18:33 |
If anyone has a riser valve lying around, could you check to see what position the weight is when it's wide open? The manifold is still too hot to work with on mine, but the weight appears to be nearly horizontal(sticking straight back). What I'd mainly like to know is does the bimettalic spring (which is gone) hold the valve closed & once heated allow the weight to open it up or the other way around? I would figure that if the valve was working, removing the spring would allow the weight to hold it wide open. I not try to remove it until it has the chance to soak a bit. I put penetrating oil on the bolts, but it's still hot, so most of it smoked off. If I can see which way is open, then maybe I won't need to take it off if I don't have to.
Richard & Carol Brown
1974 Eleganza SE
"DILLIGAF"
Lindale, Tx. 75771
903-881-0192
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GMC's don't have a heat riser valve since both manifolds flow directly into the mufflers. However, on other vehicles the spring holds the valve closed and relaxes when it gets hot allowing the weight to drop and open the valve.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] Exhaust riser valve [message #120688 is a reply to message #120625] |
Sun, 03 April 2011 12:25 |
Richard Brown
Messages: 281
Registered: May 2009
Karma: 1
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Senior Member |
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It's entirely possible that a PO put a car manifold on it & I know from looking at various pics that it shouldn't have one, but it's there big as day & from what has been said about how it's supposed to work it appears to be frozen closed. I'm soaking the studs in Liquid Wrench (Kroil not found locally) & soon I'll attempt to remove it. Since it's gotta be there to connect the pipe, I'll just gut it regardless. The PO seems to have taken more than a few shortcuts on maintenance. The carb kit I have is generic & I'm not convinced that there's all that much wrong with the carb anyway, but there is a insulating spacer in it that I plan on using. I'm dollared out for this month, so I'll be using what I have on hand for the time being.
Richard & Carol Brown
1974 Eleganza SE
"DILLIGAF"
Lindale, Tx. 75771
903-881-0192
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Richard & Carol Brown
1974 Eleganza SE
1174 Hickory Hills Dr.
Murchison, TX. 75778
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| Re: [GMCnet] Exhaust riser valve [message #120689 is a reply to message #120688] |
Sun, 03 April 2011 12:50 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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What I have done with those heat risers is to remove them from the system,
cut off the butterfly shaft, drill and tap the casting on both sides for
1/8" pipe threads and screw a iron 1/8" pipe plug into both threaded holes
until they can be turned no further, then cut them off flush with the
casting with a cut off wheel on a die grinder, throw them in the glass bead
cabinet & clean them up. I then powder coat them with exhaust manifold
ceramic coating and re install with new gaskets & brass nuts on the studs.
End of stuck butterflies. Those intake manifolds run way too hot anyway.
Nearly anything that you can do to extract exhaust heat from the engine is a
good thing. If you have a poorly running engine when it is warmed up,
suspect a cracked intake manifold or ignition before you suspect the carb.
If you wind up taking off the carb, shine a intense light source into the
manifold opening and maybe use a dental mirror or one of those little fiber
optic lenses in there and look for cracks. If it is cracked on the floor of
the manifold, remove the manifold & replace it. If you can find a toronado
or GMC iron manifold that is not cracked, block the heat passages with
stainless steel plates & be careful that the gasket does not slip when
reinstalling the manifold. Same thing applies as far as gaskets go if you
use a Rockwell aluminum one. Most guys use RTV Silicone on the ends of the
manifold. I am not the biggest fan of the stuff, but many have used it with
good results. Sounds as though someone has been under the hatch cover before
you owned the coach & perhaps replaced exhaust manifold with car components.
Check it all is my advice.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Apr 3, 2011 at 10:25 AM, Richard Brown
<wings77sporty@sbcglobal.net>wrote:
> It's entirely possible that a PO put a car manifold on it & I know from
> looking at various pics that it shouldn't have one, but it's there big as
> day & from what has been said about how it's supposed to work it appears to
> be frozen closed. I'm soaking the studs in Liquid Wrench (Kroil not found
> locally) & soon I'll attempt to remove it. Since it's gotta be there to
> connect the pipe, I'll just gut it regardless. The PO seems to have taken
> more than a few shortcuts on maintenance. The carb kit I have is generic &
> I'm not convinced that there's all that much wrong with the carb anyway, but
> there is a insulating spacer in it that I plan on using. I'm dollared out
> for this month, so I'll be using what I have on hand for the time being.
>
> Richard & Carol Brown
>
> 1974 Eleganza SE
>
> "DILLIGAF"
>
> Lindale, Tx. 75771
>
> 903-881-0192
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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