The Stovebolt Site Forums The Shop Area Engine Shop Heat Riser Counterweight and Spring

I have a 235 that I can't seem to get the heat riser to work right. The counterweight turns easily and I have a new spring. When it heats up the spring pulls away from the pin without moving the weight. I installed the spring as pictured in the book with the end tang going over the pin from the fender side. When cold where should the counterweight be, rotated up towards the block with the flat side out, or down away from the block with the rounded side facing out?

The flat part of the counterweight should be parallel with the ground when cold and the rounded part should tip toward the head when hot.

Manifold Heat Valve

1. Unhook the thermostat spring from its anchor pin and check the adjustment.

2. Proper adjustment and hook up requires only 1/2 turn of the spring from its unhooked position to slip it over the anchor pin.

Note: Should this spring be distorted in any way it should be replaced.

3. Check valve shaft to make sure it is free in the manifold. If the shaft is sticking, free it up with kerosene containing a small amount of baking soda.

From chevy.tocmp manual

The shaft is nice and free in the manifold and moves easily. The old rusted and distorted spring has been replaced with a new one. The spring was wound to only 1/2 turn before I slipped it over the anchor pin. The problem I have is that it always stays in the closed position and the weight never swings up to the open position. I can easily move it by hand in the open position while hot, but it doesn't stay and the weight falls back to the closed position.

I'm assuming your checking it while it's idling Jim? It will stay closed even when hot while idling. Crack the throttle and it should open.
Denny Graham
Sanwich, IL

Thank You Denny,

Your assumption was correct. I only checked it while idling. I wondered if exhaust pressure was needed to open it up but wasn't quite certain and never thought to open up the throttle.

If you're "lucky" like me it's rusted in the open position and you don't have to worry about it.

It's not rusted at all. It was stuck in the open position because it was all carboned up. I removed all the carbon and cleaned up the shaft along with replacing the spring. I remember when I was a kid that heat riser problems were a common cause of poor engine performance, especially in winter when they were stuck open.

I just finished doing this on my truck engine(55 235 in 46 flatbed)...these springs are getting hard to find and expensive...I also couldn't figure out if the HR valve was working, until I opened it up a little

I guess I AM lucky because it doesn't cause me any problems. I remember as a kid that most of the heat riser problems I heard about were from too much noise. Just this morning I fired her up & let her warm up because the weather's been too bad to take her out for a drive. Other than cranking a bit slow because of the cold oil she lit right up & ran fine.

Springs, they all carry the springs, pricey yep bout 15-17 bucks. But try to make it your self! I think its more than a spring, I believe its a bi-metal spring or more properly a thermostat.
Denny Graham
Sandwich, IL

I guess $14.50 is expensive for what you get but they're not hard to find. Jim Carter has them.

http://www.oldchevytrucks.biz/47_55/t1.asp?page=104