Re: heat riser valve on exhaust manifold on 1934 1103

Posted by Owen_Dyneto On 2009/7/1 15:08:39

The function of the valve is to aid vaporization of fuel during cold startup by diverting exhaust gases against the base of the intake manifold, sometimes called the heatbox. If the valve is inoperative but stuck in the open position, the only negative will be slightly poorer performance for a few minutes while the engine warms up. If the valve is stuck in the closed position, you'll basically be constantly heating the fuel mixture and indirectly the carburetor which could lead to vapor lock, gasoline boiling within the fuel bowl, etc.

The spiral spring is bimetallic which is to say it winds or unwinds with the application of heat. In a cold engine at rest, it is holding the flapper valve in the closed position, as the engine warms, it relaxes and the counterweight on the other side insures that the valve begins to open. The little coil spring is probably just an anti-rattle spring.

If the shaft is free to rotate, you might want to just buy a new heat riser spring and repair it. If the shaft is frozen and you don't know which position it's in, you'll face removing the manifolds to free it up unless you get fortunate with some PB Blaster and a bit of physical persuasion.