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Jul 21st, 2025 | | | | Joined: Sep 2010 Posts: 695 Shop Shark | | Shop Shark Joined: Sep 2010 Posts: 695 | I was wondering how critical the counterweight butterfly flapper valve was, in the exhaust manifold of my '59 half ton's 261... I'm thinking a 235 should be the same.
Would it hurt to remove it in it's entirety and plug the holes where the shaft rotates?
I'm not sure what purpose of design this item is and because of it, I'm looking for an exhaust manifold. Should I be?
Thanks in advance,
Jerry | | | | | Joined: Nov 2005 Posts: 6,061 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 6,061 | Hy Hellomrwilson, as a famous GM engineer once said "Parts left out cost us nothing, and cause us no service problems", what he meant was, if a part was on a vehicle the manufacturer of the vehicle felt that part was required for the vehicle to operate with no problems for the majority of users of that vehicle. The exhaust flapper was designed to send some heat up to the intake manifold when the engine was cold, this would hopefully prevent carburetor icing. As the engine/manifold warmed up the bimetal spring on the butterfly shaft opened the exhaust flapper to allow a more unimpeded exhaust flow. Personally I wouldn't remove the valve from the exhaust manifold, hope that helps. | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | The heat riser valve promotes quick warmup by directing exhaust gas against the bottom of the intake manifold when the bimetal spring on the shaft is cold. As the engine warms up the spring heats up and allows the counterweight to turn the flap valve to direct heat away from the manifold to prevent vapor lock, etc. with a hot engine. Removing the flapper valve will result in slow warmup and rough running when cold, and possibly vapor lock and percolation of fuel out of the carb float chamber due to overheating the carb on a long run or a hard pull with a heavy load. It's better to fix the heat riser or find a manifold with a good one. A 235 exhaust manifold should work with no problems.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Sep 2010 Posts: 695 Shop Shark | | Shop Shark Joined: Sep 2010 Posts: 695 | Thanks guys, I figured the flapper worked similar to a thermostat and being from South Texas I wasn't concerned about extreme cold.
The excess heat to the carburetor is another story. Thanks for the input!
I've also posted in the parts wanted category.
Hopefully something will turn up.
Jerry
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