The Stovebolt Site Forums The Shop Area Engine Shop heat riser

I got the heat riser freed up on my 64 w/230, but it had no spring at all. I stole one off a later model but I'm not sure if its wound correctly. It flops open(?)(down) under acceleration. Is this correct? Thanks, Brian

The heat riser should close the damper when the engine is cold, routing the heat up toward the intake. As the engine heats up, the weight on the shaft should overcome the spring and route the exhaust gas straight down the exhaust pipe. If it opens on acceleration, the spring is wound correctly. If the valve is staying closed with the engine at normal operating temperature, the spring is too tight.
Jerry

Thanks, HRL. I am 35 & have never seen one that wasn't stuck. Any source for new springs? Brian

Back in the dark ages when I was growing up around the family shop, freeing up the heat riser valve was part of every tune-up. It's pretty important for proper warm-up, routing exhaust gas under the carburetor before the engine reaches normal operating temperature. One stuck in the closed position heats the mixture all the time, resulting in a too-lean mixture during operation at normal running temperature. I don't know of a source for replacement springs. A bimetal spring from a junked automatic choke might work, they operate on the same principle.
Jerry

Chevy Duty sells replacement springs. So does American Classic.

Chevy Duty , Engines, page 10

Thanks, all. Brian

On my Chevy (1954), the spring on the carb automatic choke fits the the heat riser very well.

Except for the fact that it's wound in the wrong direction! So, at least for the Rochester BC carb, this spring certainly won't work.

OK Jerry, this seems to be my day to press you for details. I thought the heat riser moved fresh air past the exhaust manifold to warm intake air for the carb until the engine was warmed up enough to run right. I have never heard of nor seen one that actually reroutes exhaust gasses.

Please enlighten me. :confused:

You would need to dismantle a stovebolt intake/exhaust manifold assembly to see the exhaust gas routing. There is a flap valve that directs the exhaust against the bottom of the intake manifold when the engine is cold, helping to warm the intake mixture and keep the gasoline vaporized. Once the manifold heats up, the bimetal spring relaxes, gravity takes over and pulls the weight, and the flap valve down, and the exhaust is directed away from the manifold and straight out the exhaust pipe.

On a V-8, the heat riser partly blocks off the outlet of one exhaust manifold, and directs some of the gas up through the center of the cylinder head, under the carburetor, and out the other side. Early models had the same bimetal spring/weight combination as the 6-cylinders, while later heat risers were vacuum-operated, using a thermal/vacuum valve and a vacuum motor to open and close the heat riser flap. Those valves are called "E.F.E." valves, (early fuel evaporation). In either type of system, the exhaust gas is routed right against the intake, to keep the fuel vaporized during warmup.

Another type of exhaust heat system involves pulling fresh air through a passageway in the exhaust manifold, and applying it to the automatic choke in the carburetor. This is called a "choke stove", and does not involve routing the exhaust to the carburetor, just heated air.
Jerry

Ohhhhh. So what I have been calling a heat riser all these years is actually a choke stove and a heat riser is something altogether different!

Like you say, ignorance can be fixed, stupid is forever.

Thanks

PS (Sorry about rousing the rabble on the transmissions, I was just trying to get straightened out. I was thinking that I was planning on spending big money on something that you were saying would devalue my truck. What I learned is there are plenty of guys on both sides of that one, so if I want a stick, somebody would probably buy it, should I have to sell it.)

No problem!
I've been known to stir the pot a little just to get a discussion going! I prefer automatics when possible, but it depends on what an owner plans to do with his truck. A real creampuff original-condition truck doesn't need to be butchered up with modern running gear, but if it's a refugee from the boneyard, then things like a V-8 conversion, independent suspension, tranny swap, and new rear end, brakes, etc. don't really make a difference. The Dana type 60 rear end in my 59 Burb has a Chevy housing, Ford gears, and a Dodge pinion flange. I'm going to install a Cadillac 500 engine, a turbo 400 transmission, and a 3/4 ton mid-70's Chevy IFS in it before it goes back on the road. It's also getting the tilt/telescope Caddy steering column and 6-way power bucket seats before I'm done!

Another project is going to involve a Cummins turbo Diesel inline 6, with a New Process 235 4-speed, in an early-50's frame. The body is going to be a 55 1st. series a neighbor just gave me. I haven't decided if I'm going to go IFS with that one yet.
Jerry

This 230 really purrs like a kitten, one of the reasons I had to have this truck. I could tell it had been built, cheap paint flaking all over, quiet, no smoke, but couldn't run it long as all the freeze plugs were rusted out. I gambled, pulled it, replaced all freeze plugs & clutch. Rebuilt the B, replaced the fuel fouled plugs. Starts with a bump of the key, no leaks or noises. I am officially a Stovebolter, I really like this engine & have no intentions of a V8. Thanks for the help. Brian

Hey Hotrod,

I have been thinking about a cummins 4bt with a sm465 in my big bolt... so I'd be intrested in hearing more about that diesel conversion...

-Mike R.

These engines are kind of oddball, 120 HP inline 6-cylinder turbo diesels, with the horsepower rated at 3,600 RPM, pretty tight-wound for a diesel. I've had one on my dyno, and they make the HP they're rated for. A good injection pump shop could probably bean it up some without overstressing the engine. They're take-outs from UPS vans, originally designed as power generator engines by Onan, and inherited by Cummins when they acquired Onan. They were used interchangeably with Chevy 292's and Ford 300's by UPS, with just a fuel change to make the vans diesel-powered. The engines ara approximately the size of a 292, and just a little heavier. I've got 4 complete, running-condition engines, and one parts engine which is missing the cylinder head. The bellhousings are the old hydraulic-clutch types used on late-50's Chevy V-8's, with the throwout fork on the passenger's side. Any standard-shift 4 or 5 speed with a standard Chevy bolt pattern will bolt up. The clutch is the Chevy heavy-duty 12 inch type. I'm thinking I can also adapt a Chevy-pattern automatic, either turbo 350 or 400, if I don't want to run the stick shift. A belt-driven vacuum boost pump from a GM engine like the Cadillac 262 cubic inch V-6 will handle the brake booster if I decide to run power brakes.
Jerry