exhaust manifold valve

[Guest imported_NikeAjax]

The exhaust manifold valve is all-crapped-out on my ?56 Century, its shaft isn?t holding the backpressure and is rattling like a marble in a coffee can: I?d like to replace it. Is there a kit or something out there to replace these or do I have to have someone fix this for me at a shop?

Thanks,

Jaybird

[The Old Guy]

The easiest fix is to weld it in the open position. Unless you drive your Buick in the winter, it is not necessary.

[NTX5467]

If the heat crossover in the intake manifold is not carboned-up or otherwise restricted, you could already effectively have a "blocked heat riser" situation (i.e., a "cold" manifold). In that case, as I found out, it can magnify the exhaust pulses in the manifold with the heat riser mechanism. Things are far from smooooooth in those pressure pulses!

In the '60s and '70s, when heat riser valves would rattle (and people didn't like it then either), this was a good thing as it usually meant the valve was still working. If the shaft's bronze bushings in the exhaust manifold were too tight, then "no rattle" meant "no workie" (due to the friction drag of the bushings on the shaft) eventually.

In my case in my '77 Camaro 305, the vacuum operated heat riser "actuator" started rattling loudly. The rod had come off of the ball stud on the heat riser valve as the ball stud was now oval-shaped instead of being a "ball". When we changed the engine several months later, the exhaust crossover in the intake was solidly carboned up (after 400K+ miles). When we could keep the rod on what was left of the ball stud, it was quiet, but otherwise the unrestricted valve would violently swing open and closed against it's residual spring pressure (due to the exhaust pulses being "pulses").

Your existing heat riser thermostat spring might be having some age issues, but I suspect (from my experiences mentioned above) that there might be something else making it worse than it should otherwise be. In many cases, a "cold" manifold might not cause any driveability issues in the colder times of the year, but you might need to also tweak the automatic choke adjustment and use some of the fancy spark plugs to mask the warm-up driveability issues that might result from less exhaust heat in the intake manifold. The degree that these issue might happen is somewhat variable (fuels, air temperatures, carburetor issues, "state of tune" issues) from vehicle to vehicle.

Tacking the valve "open" is an old hot rod trick that many have used in other situations too. Whether you check the heat crossover in the intake or remove the exhaust manifold, there'll be some work involved.

Just some thoughts,

NTX5467

[Guest imported_NikeAjax]

The engine is super clean, inside and out, as I rebuilt it this spring, late summer, myself. The shaft is worn out, it gets smaller as it goes into the hole. You said something about a spring: what's that? I don't got no stinking spring! The thermostatic spring is gone, which is why I was wondering about some kinda rebuild kit for it. It rattles so bad that the exhaust leak makes the car run rough.

I live in San Jose, CA, we have better weather than anywhere, hands down, so I'm not too worried about not having this valve working. It's an everyday driver too!

Thanks!

Jaybird

[NTX5467]

I'll admit that I have no knowledge of how the spring should be configured, but one from something like a '69 or so Chevy might work as it's just a spring that wraps around two pegs, one on the valve and another on the butterfly that's attached to a counterweighted shaft. If the shaft has that much wear on it, it might be best to find a repair kit or similar NOS part? Otherwise, brazing it up might be the best alternative. A little manifold gray paint after a little dressing of the braze and that might take care of the whole deal.

Just some thoughts,

NTX5467