The Stovebolt Site Forums The Shop Area Engine Shop Heat Riser Question (Chevrolet 235)

What problem if any would arise if the heat riser on the exhaust manifold is stuck in the "slightly open" position? At present it is rusted stuck in there and I have just under 1/4 of an inch opening, letting hot exhaust up into the Intake Manifold. I'm letting it soak in Kroil overnight and will gently tap it with a hammer and repeat as needed. But wondering, just in case i cannot get it freed up, is there anything to worry about? My truck is a 1948 Chevrolet 1/2 Ton. I'm running it with a 1962, 235ci motor, with a 1 barrel Carter YF Carburetor. Thanks in advance for any insights.

Shop manuals are awesome.
In this case, the year doesn't matter. Kroil works. So do properly applied hammers & O/A torches (edit- don't use a torch if that Carter is plumbed & full of gasoline).
Brad

Thanks Brad, I'll try it out. No worries about the fuel - the manifold, carb, etc is off the engine...

Bobby, you'll be able to free it up if you are persistent with the Kroil and the tapping. Don't worry about having issues if you can't get it to work...you'll be successful getting it to operate. Sometimes it takes several days of applying the Kroil and tapping, so don't be in a rush. It just takes patience and persistence.

Matt

Thanks Matt - great news to report, got it free!! I had to use my dremel to grind out some carbon inside the manifold around the flap - and used the torch and kroil on the steel rod. Heated it for 2-3 minutes at a time, put the kroil on, waited 10 minutes, came back tapped it with a hammer, repeated this about 4-5 times over 3 hours and finally it loosened up and now is totally free. Appreciate the tips!

1 more Question: So, the way this thing works, is it the heat makes the brass spring/coil shrink, and thereby the combination of the exhaust gasses and the weight gadget on the outside, pushes the flap into the CLOSED position. So when it is cold or not yet hot enough the brass coil stays expanded, which forces the flap to the OPEN position which catches the exhaust gas and pushes up and around the intake manifold? The reason I ask this question is that I heated my brass spring coil and it shrank, but I noticed that doesn't move the flap, but it would allow the gas inside to push it shut if it were blowing. On the other hand, when the brass coil is cold, it expands back out and that seems to keep the tension on flap in the open position.

Spring gets hot, valve closes.
Trying to describe anything else is going to get confusing, but when the thermostatic heat riser spring is cold... the valve should be open (thus directing heat to the intake).
Brad

I had to edit, so I got confused too

The springs have a small bend on the end that catches a slot in the heat riser shaft. If the bend is missing, then the spring is just along for the ride and the flap will set where the exhaust can get out the quickest way it can.

Video Of the heat riser spring in action.

(This video idea is credited to DADS50- mine is just a different angle) I angled the viewpoint to show the heat valve opening & closing.
Edit- I am aware this thread is settled, but the video "explains" a lot instead of wording it into confusion. Somebody chime in if the one I have on video is not functioning correctly...

Brad

I wedged mine in the heat on position once trying to figure out why the truck was running so poorly (spent a month and changed everything, still don't know what was wrong, it just started running like its old self one day) It was definitely the wrong thing to do, it spit and popped, I pulled over in the les schwab parking lot and UN wedged it pretty quick. So heat constantly on is bad.

Brad and/or DADs50 - good video on the heat valve. I never quite understood the working of the valve but this really helps out. Thanks!

The heat valve is stuck in my 235 ( I have had no luck getting it free) , and though the engine seems to run fine, was wondering if it was stuck in the open or closed position. It appears from your video that if the weight is horizontal, the valve is in the heat on or closed position. I guess that is where mine is. For some reason, I do not have the problem that brokenhead had with his valve wedged closed. Thanks for the post.
Lee

Lee,

Give this thread a quick read. (CLICK) It's loaded with heat riser info.

I ran a stuck one for 20,000 miles in a 216 and had no real issues. It did sputter a bit when it was real cold out if I tried to take off before the engine warmed up, but I seldom do that anyway. It didn't take long to clear up and run right. Our climate is on the mild side, so your mileage may vary, as they say.
One neat feature of the design of the fully functional one is that when you goose the gas in the cold condition, the rush of the extra exhaust pressure pushes the the flapper into the warm position momentarily to allow better driveability under acceleration.

To install the spring, do I need to put some tension on it before sliding it into the slot?

Hello, Tom,

The spring "setting" is decribed on this page in the Shop Manual.
About a 1/2 turn (it will expand and then open the flapper when warmed).

Good luck,
Tim

Mine was stuck real bad too and finially got mine broke loose and checked the rod out it was worn real bad on the ends that went through the manifold, and ;I built one out of s/s rod and flapper and drilled the flapper to the 5/16 s/s slick rod,This was what Hotrod Lincoln suggested. a very smart guy and got to stop by and visit him today, Great visit. Moonshine Mike