Heat Riser Valve, or what Chevy calls the Manifold Heat Control Valve...

Quick follow up. I finally got the spring installed in the right orientation, I tested it under hot and cold water to see which way it turns when heating and cooling, (the kitchen sink is enough to see which way it will turn) and it works perfect, with the engine running it opens to the vertical position after 5-10 mins of warm-up and returns to horizontal once engine cools! I used the Jeep CJ spring from Summit Racing for around $12...

I had more fun with the heat riser valve on my '67 V8.

The van's been down on power lately. Not sure why, so I checked the old heat riser valve to see if the butterfly had spun at all on the shaft. It hadn't but it appeared that the valve wasn't opening much at operating temp. So I decided to replace it with a "new" heat riser valve I got off Amazon. That one was even worse. It looked great, and fit fine, but as soon as I drove the van the shaft froze and I notice the spring had too much pull even when hot. I took it out again, adjusted the spring, and used solvent to free up the shaft. This time the spring seemed OK but the shaft froze again. Finally I figured it was as lemon. I got out the spot welder and attempted to make sure the old valve was secured to the shaft on the old assembly. Move the anti-rattle spring from the new valve to the old one. Adjusted the spring on the old valve for minimal pull when cold. Enough to close the valve but no more.

This time the valve seemed to work fine and as before the old valve didn't seize up after just a few test drives. Power still seemed down so I replaced the fuel filter just in case. It seemed to help but that might be a little subjective. Might be a little more peppy at low speeds, though.

Timing checked out ok. Haven't done a compression test lately (it's a bear to do on these doghouse V8's). Next step may be to re-check the hydraulic valve preload. It may have closed up again. We'll see. Van's been on stands since the exhaust valve work to replace the front spring bushings. Once that's done, I'll be able to do some more testing.

Meanwhile I have the "new" heat riser valve whose sole value so far has been to donate an anti-rattle spring to the old valve. Maybe the bimetal spring will be its next donation. Worst case, I'll cut off the butterfly valve and use the thing as a "delete".

,,,,are the points set right,,,,,,does the rotor twist and spring back on the centrifugal advance,,,,,,is the vacuum advance working,,,,,

Good question. No points to worry about, it's an electronic ignition setup. Don't know about the centrifugal advance. The vacuum advance seems to be working, at least it gives a boost at idle and advances with rpm when connected, more than when disconnected. Something worth looking at again, though.

You guys have so much more patience than I. I have the heat riser, round, on the end of the manifold and it was stuck closed-ran like c***. Anyway, got it free yet could not find a replacement spring in the time I had to fix and just don't like them any way as my G10 mostly sits out the winter (won't take her out with any salt on the roads and DC is crazy for salt. Sometimes the salt is actually thicker on the streets than the snow). So, I just locked the cam open with Stainless safety wire. Might take a little longer to warm up but she runs much better. And, since these 6s tend to run hot anyway I doubt I'm killing the environment any faster. Good suggestions tho next time I pull the manifold.

Well, ChevyVanMan,

As it turned out the problem was primarily on the carb side, which I think I detailed in another thread here. In summary,

1) Before I got this van in 2008, someone replaced the stock master brake cylinder, which was good, except the one in there seems to be longer than the stock one. The net result is that the throttle linkage bumps up against it at idle, resulting in the gas pedal being lower to the floor than it should. This in turn results in only about 1/4 open throttle when the gas pedal is floored. There wasn't any more linkage adjustment I could do to compensate for that. So finally I fixed this by taking out the part of the linkage at the pedal, which is a pivot arm, and putting in a shop vice and just twisting it so that the pedal would sit higher. Had to do this in stages until I got the desired "lift" and WOT.

2) The carb rebuild kit I used back around 2008 had a defective accelerator pump. It seemed to fit OK but in time the nylon body seemed to soften and this allowed the delay spring to separate the pushrod from the body. The net result of that would be that this in turn would block the throttle from opening fully because it's all linked together. I got a new kit from Mike's Carburetors online. This had a better design with a metal collar around the nylon body to prevent it from releasing the pushrod. However i also ordered a separate pump with a slightly shorter push rod. This one came with a new spring (the rebuild kits make you use the old spring). This other pump seemed to work better than the one that came with the kit, so that's what's in there now. Van has plenty of power... it will spin the rear tire(s) on turns if it give it too much gas. Van easily gets up to 70+ on freeway now, although it does guzzle down the dino juice when that happens. It also makes it up hills at lower speed in 3rd just fine. BTW, the pump that was in there when I bought it, and the one in the first rebuild kit, didn't actually pump much because the rubber cup was too small to contact the walls of the pump well. The new kit and new pump have expansion springs inside the cup that make sure the cup touches the walls and that it's pumping properly. Who would have guessed?

To date no more problems with the heat riser valve - it seems to stay nice and free moving with a minimum of maintenance. Unlike the cheap replacement I got off Amazon. There was some ticking going on which I figure was some exhaust leakage around one of the joins, but that seems to have gone away now. One of these days I'll get back under there and make sure everything is lined up and sealing properly.

So in other words I'm not quite ready yet to defeat the heat riser valve. I figure it serves a purpose, even in mild weather. I'm not concerned that when it's working properly that it presents any significant obstruction to the exhaust flow, at least not for street use.

Didn't know the sixes ran hot. This V8 seems to run a bit hot, it's got a SW temp gauge that consistently reads 190 plus when warmed up. I figure that's probably because someone stuck a 190 thermostat in there. The Chevy service manual specifies a 180 instead. One of these days I'll open that up as well and see what's in there and bring it back to a 180 if it's not that already.

Probably the most important smog device our oldies lack is the charcoal canister for recycling gas vapors. I'm not a scientist yet I do know unburned hydrocarbons are much more damaging than burned hydrocarbons--hence oil spills in the oceans are usually set ablaze--no matter how much smoke they put out. So I suspect a little slower warm up on our oldies makes pretty little difference to the demise of our planet. All in all we use much less energy by keeping the old ones going than by buying something new. Afterall the cost of a new vehicle is mostly the energy it took to make. Commodities like steel, rubber, glass and plastic are all relatively cheap. Getting them to run down the road--now that's expensive.