The Stovebolt Site Forums The Shop Area Engine Shop Heat Riser Valve

Hi Folks,
Hope this is an easy one. Need some info on the heatriser valve on my 235 I6 in my 55 second series.
Seems to be working OK. Starts and runs OK. Runs well when warm but still have a rattle above 2000 - 2500 RPM. A friend suggested I look at the heat riser valve. It was then that I realized I don't know what to look for!
Is there any way to tell if the spring is
correctly installed just by looking at it?
Does the external part of the valve (looks like a weight) change postion between warm and cold? If I grab the weight should I be able to move it easily?
Many Thanks

Read this over and I think it will clear it up in your mind:
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0604.htm
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0620.htm

Denny Graham
Sandwich, IL

Yes it should move, very easy! When cold, blow some hot air on the spring, it should unwind once it warms up.

joe

Correct me if I am wrong but I believe there are actually two springs. One is the coiled bi-metal spring that opens and closes the valve and then a plain coil spring on the end that is an "anti-rattle" spring.

too funny.

just today i discovered that the hear riser on my 50 is stuck closed.

looked at a bunch of your pics denny to get a better idea of how it is supposed to look. can't seem to get it un-stuck so i may have to take the intake/exhaust manifolds off to get into the space and free it up.

not sure i really need one here in arizona but i should make it right.

sepp, here is a link to some reference shots of the heat riser.

http://www.pbase.com/dennygraham/image/112537670

bunch more to look at there too if you have the time.

p.j. those all stick and seize. I finally bit the bullet, pulled the manifolds and made a stainless steel shaft and stainless steel bushings for my '36 Chevy pickup heat riser about 30 years ago and that permanently cured the problem.

Ray

Many Many Thanks!
The Denny Graham pictures helped a lot.
My thermostatic spring was installed backwards and was holding the valve wide open.
I previously said that it runs great - hot or cold - BUT I have never driven in really cold winter weather.
One thing I did notice was that the incorrectly installed t'static spring was installed with a lot of pre load. More than one turn. Is it possible that with the valve "jammed open" that this could be causing my rattle above 2000 RPM?
As soon as it stops raining I'll go out for a test drive. Another thing I noticed is that the spring slot isn't very deep. The spring sits precariously at the end of the shaft. Is this common? Could I lose the spring while on the road?
Thanks Again

Morning Sepp and P.J.,
Lots O' people will tell you that if you’re operating your truck in a warm climate that you don't need the heat riser. So believe what you will, but we’re not talking about a choke here but an automatic device to get the manifold up to temperature so the fuel will vaporize rather than condense. Even though the engine is sitting out in the 90° sun, that’s still not hot enough to vaporize the fuel as it travels into the manifold.
Take a few drops of gasoline and splash it on to a warm iron surface and then onto a hot iron surface and difference is quite obvious (NO OPEN FLAMES HERE). The longer you delay this the longer you will have fuel pooling in the manifold. This washes down the cylinder wall and dilutes the crankcase oil. It can take 15 to 20 minutes for the engine to come up to temperature, and that long to heat the intake manifold without the heat riser operating. The intake comes up to temp much sooner with the heat riser operating like it was designed to do.
So, keeping it free and adjusted properly in any climate will add many miles to your engine.

Sepp, if your spring is just sitting at the end of the slot 9 times out of 10 the old spring as broken off and a piece is still in the slot. If you try spreading the slot in the shaft 9times out of 10 you will break one of the legs off the shaft. The thermostatic coil is originally slipped all the way to the bottom of the slot and then it is squeezed tight. Again, the shafts break very easily when you try to spread them, BE CAREFUL!

Denny Graham
Sandwich, IL

Huh, starting to wonder if I made a boo-boo yanking that thing out (spring was broken anyway). Thought it was just some pollution control device. I did install the solid gasket that came with the kit that totally covers the square'ish hole in the bottom of the intake manifold.

Anyone really notice a difference in warm climates (Houston) without one or one stuck open?

This one's for Denny Graham....

Denny,
Am I correct in thinking that as the thermostatic spring gets warm it softens and the counterweight pulls the valve open?
I reinstalled the spring as per your pics and was thinking that if the spring contracted when warm it would hold the valve closed.
As installed per your pictures, when I warm up the spring with a heat gun the valve opens. It closes fairly quickly (after approx. 1 min.) when I take the heat away.
Whatever, it's definately opening and closing. I'm just curious about how the spring works.
You are right about a piece of the old spring in the slot. In fact, it looks like two pieces side by side. Think I'll tackle that over the weekend.
Thanks Again!

No, the coil is actually a bimetal strip, which is two pieces of metal having different expansion coefficients. They are laminated together and wound into a loop. When the coil is heated one side expands more than the other and the coil winds tighter. You adjust the coil by tightening or loosening the coil to reach the proper balance between the tension from the coil and the weight. The operation is explained in the Truck Shop Manuals.
Again, BE CAREFUL when spreading the shaft, they break real easy, then you’re sunk.

My only answer to the belief that the thermostatic control is not needed is, that the bean counters at GM would never have allowed the engineers to have wasted the material and time on it for all those years that it was part of the system if it weren’t necessary. But, I guess some backyard mechanics know better than a staff of GM engineers with seventy or eighty years experiance. Might I also add that every other engine manufacturer equipped their engines with a heat riser also. So as I said, believe what you will, it’s your engine.
Denny Graham
Sandwich, IL

green farmer,

i really don't know how long my heat riser has been stuck in the closed position, but if it has been a long term issue that i haven't noticed before, it could explain a mysterious hard starting after warm-up in the summers here in arizona.

going to pull the manifolds off tomorrow and get the valve freed up and operating properly so we will see if it makes a difference.

sheesh denny... them engineers don't know nuttin'

I noticed that my heat riser opens just after the engine is too temperature.I have watched it over and over and find that fascinating.darn,don't take much to entertain me !


Tim

stovebolt t.v. ?

sepp hope you don’t mind me jumping in this thread.

after reading some of the post here I went to the garage and warmed up the truck. Looked and the spring and weight on the riser, and the weight didn’t move when warm. This was just idling for about 15 minutes.

When I lifted the accelerator rod on the carb the riser went to the closed position. but when I let it off the weight went back to open.

Is this correct?
or when warmed up should it close and stay closed regardless if giving gas or not.

1950 3100, 235, 216 intake exhause.
Thank you

For DADS50
Hope this helps...
Sounds like your heat riser is opening and closing which is good.
I can only guess that there may be some interference between the accelerator rod and the thermostatic spring. On my 55 series two these parts are very close together. Removing and installing my spring brought this to light.
If your engine is warm, the valve should stay OPEN whether giving gas or not. However, it cools off quickly and if it was only an "idle warm up" you may have not gotten it warm enough to stay open.
I think Denny Graham can help you more than I can. His answers really set me straight.

no interference between the rod and spring plenty of clearance.

but I did notice some damage to the spring there is a little nick on the edge

pic

pic 2

Thanks

The Coil is wound to Loose Dad, that will hold to much bias on the weight, tighten it up a little at a time till it's open when it starts to show some temperature. The weight should hold it open once it is warmed up and the hook on hte coil will be off it's stop a little in most cases.
That nick shouldn't hurt anything, the coil can be wound tighter or looser till you reach the correct ballance. The biggest problem with them is they rust and break off where they go thru the shaft because that is the point of highest stress.

Denny Graham
Sandwich, IL

Denny,
Got my heat riser working correctly.
Have one problem left. How do I get the broken piece from the previous spring out of the slot?
Spread the slot with a flat bladed screwdriver VERY CAREFULLY. Actually saw light along the flat side of the broken off piece but couldn't budge it. Tried everything I could think of including a box cutter knife, compressed air, very small punch and light hammer. Nothing worked! Am I missing something?
The new spring only slides into the slot about the width of the tab. Everything is working correctly but I know it will fall out if I drive it as is.
THANKS

The original spring was simply inserted into the slot and the shaft squeezed shut. Over time the shaft and the spring surfaces rust and they appear to be welded together, they're not. However a bond does form between the two rusted sufaces but it should break loose if you mess with it long enough. You have to spread the slot a LITTLE to get it out, but many of them are rusted at the bottome of the slot and that is already an area that can't take much bending even when new.

And I can't empesize enough; "BE CAREFUL when spreading the shaft, they break real easy, then you’re sunk."

Denny Graham
Sandwich, IL

o.k. guys. we are back to this issue.

over the last few days i have been attempting to get the heat riser valve freed up so it operates as intended. in spite of many suggestions that i just leave it as is or weld it in place (which it already is) or cut it out entirely, i want it to work as designed.

at this moment it is still stuck. solvent, a little heat, gentle tapping...nothing so far.

any suggestions?

Hi, I also have a stuck/seized manifold heat valve as it is called in my 48 to 51 truck shop manuel.( Re page 6-20 ) It says to use some kerosene with a small amount of baking soda to free it up. Has anyone tried this and what was the result.

that is what i am thinking about trying next...

free at last. free at last! great god almighty it is free at last!

tapping, pb blast, a little heat, tapping, heat, pb blast, vise grip, wrench, hammer...

it is free! and the best part. i didn't break anything in the process.

All the talk about this topic mentions the 1948 to 1951 manual. Does that mean a 1947 doesn't have this valve?

I know that all 216 motors have them, cars and trucks both.

No Rusty, just that the shop manual reprint that 90% of the guys are using is the 1948-51 Truck manual that's sold by the vendors. Chevs of the 40's has a shop manual for just about any years car or truck.
DG

PJ, it may be "Free at last" but it is not free for long. We've all been through this. The only permanent fix is a stainless steel shaft and stainless steel bushings in the manifold itself. I did it the hard way. Freed it up. Installed the manifold. Fought the losing battle. Then finally did what I should have done when the manifold was sitting on the work bench.

My '71 Dodge van came with the stainless parts. That's what gave me the idea to make stainless parts for my '36 Chevy.
Ray

If something more was needed gm would have done it 50 years ago. If its lubed once in the while it will be fine.

i guess it is all about the little victories then...

regardless of the benefits of stainless steel, i am pretty sure the riser has been in the "stuck" position the entire time i have owned the truck and it ran fine. maybe now it will run better or maybe it will run worse. either way i have to go on the belief that i have improved the running condition. i will know the results of my efforts tomorrow when i get it all back together and fire it up.

thanks for the support.

After looking at the diagrams and photos I find myself getting confused (which isn't hard to do). In the shop manual the diagram shows the valve closes when warm (figure on the right)which would mean a counterclockwise turn from the open position (when cold - figure on left). Denny's photos showing the Butterfly open (cold)would result from a clockwise turn from the butterfly closed (warm)Should the 'closed' and 'open' labels in Denny's photos be switched? Or am I confused about what 'open' means (warm or cold)or what closed means (warm or cold)One of the labels on Denny's photos of the spring says butterfly held closed when cold. And if the valve is stuck, which position is it better to be stuck in-open or closed? (i.e cold or warm)? Mine appears stuck about 1/2 way.

When the truck is cold the plate should block off the hole and direct the hot exhaust up to heat the carb. As the engine warms up the spring allows the plate to turn so the exhaust can go straight out into the exhaust pipe.

PJ, I'll be interested to see if the shaft remains unstuck. I've owned my '36 chevy pickup since 1965 and before I made the stainless steel shaft and bushings I asked many others whether they had a solution to the sticking problem. Most of the people I asked had no idea what I was talking about when I said "Heat riser valve". Every one of those who did know what I was referring to said that theirs was stuck and they simply live with that.

Those may not stick in a daily driver because the daily rotation of the shaft polishes off rust as it forms, but my '36 is only driven occasionally. That used to give it time for rust to form and rusting involves an increase in volume so the shaft would seize in the manifold.

I still remember tapping the end of the shaft and the counterweight with a small hammer and spraying in heat riser lube to free it up to no avail.

The same thing happens to my 1952 Ford 8N tractor that I use to smooth my gravel driveway. In the winter when there is a lot of humidity in the air the clutch disc sticks to the flywheel as rust forms unless I drive it at least once every 2 weeks. That problem is even mentioned in the tractor owner's manual. The manual recommends blocking the clutch pedal in the disengaged position to keep the disc from sticking to the flywheel in the winter. Even that didn't work for me. Not letting it sit for over 2 weeks proved to be effective.

Rusty print the page 6-4 from the shop manual, and the photo I posted in my allbum. Put them next to each other and it should become a little clearer. The arrows in my picture are showing the direction of gas flow, not the direction of rotation, this may be what is cornfusing. I probably could have labeled it differently. http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0604.htm http://www.pbase.com/dennygraham/image/112537670
From the front, looking back, the weight is rotated by the thermostatic spring in the clockwise direction routing the gas up to the base of the intake manifold then down out the exhaust manifold. As the bimetal strip warms and expands the spring tension eases and the weight rotates in the counter-clockwise direction closing off the intake and deflecting the gases straight downward and out the exhaust.

Good you got it free p.j., your lucky. That’s 99% or the battle. Now you just have to get the thermostatic spring adjusted. It’s been my experience that they will stay free if you check it at regular intervals and just make sure that its free and isn’t sticking. The problem comes in when it is allowed to stay stuck for a period of time and rust and carbon build up. The oil will burn off, but it won’t hurt to oil it up when it’s cold and work it thru its full rotation every few hundred miles to knock the cobs out.
Denny Graham
Sandwich, IL

The valve on mine is not stuck, but we have been suspecting it's operation might be less than stellar.

today I put the heat gun on it to heat up the spring, and the spring moved. It un-wound at the end and removed itself away from the mounting pin. the counter weight did not move at all.

I thought the spring might be on backwards, but it's on there just like the pictures.

Something is not right but I don't know what.

So, at rest, cold, should the weight be up? or down? Does the spring hold it into position cold, then moves it hot?

more confused than ever now...

Thanks, Denny, the arrows showing the flow make sense.

Great Rusty maybe I should re-label that photo for anyone that might reference it in the future.
Scot, take a look at the two links that I posted earlier. The thermostatic spring should unwind and even come off the peg, that's normal; this allows the weight to open the deflector valve route the exhaust out its normal path. If the weight is not rotating counter-clockwise (from the front looking back) then there is some obstruction in the exhaust manifold. Either the shaft is rusted in the casting or there is carbon buildup inside.

Denny Graham
Sandwich, IL

I checked the links/pictures again. thanks.

the counter weight on mine is always down to about horizontal. I can pick it up about 45 degrees or so. It is down when cold, and when I put heat gun heat on the spring, the weight did not move, but the spring unwound off it's peg.

Is the spring intended to hold the weight in the UP position, then when it gets hot, it will relax and let the spring unwind, and the weight to go down? thats what it looks like it should be doing, but its not.

The weight is always down, and stays down,
so I guess my heat is always off?

Well then,, if it is always off, then this is not the cause of my carb boiling over issues....

My manifold gasket kit came with 2 gaskets for connecting the intake and exhaust manifolds - one was an open design, like a square ring, the other a flat plate, solid all the way. My riser valve was broken so I simply removed it and welded up the shaft holes, and then used the gasket that blocks off the bottom of the intake manifold from the exhaust gas.

Anyone ever done something like this and how'd it work if so?

I've been able to free mine up but it it not free wheeling (yet). I'll work on it a little more. I thought I could have it open when cold then manually close it after driving for a while. Any suggestions as to how long I should drive before moving the valve? Thanks