Heat Riser for 250 ci. Straight Six

[Stock72c10]

The heat riser on the exhaust manifold on my 1972 250ci straight six is shot. The counter balance is hanging and the spring is shot. I have two questions, is it even necessary, I run a manual choke, or can I just wire it to the manifold in the open position? Secondly, what is the open position? I take it it is when the counter balance weight is hanging down? I would rather not take the exhaust manifold off to find out.

[Palf70Step]

I ran mine fior two years without it, although it does not get as cold here. You don't need it, it just makes the vehicle a little less cold blooded when you first start it up. After you are up to operating temps, it serves no purpose really.

I don't remember what position is opened, since I don't have the 6 any more.

[Stock72c10]

My manifold has all the parts for an automatic choke, but the PO said he couldn't get it to work correctly so he installed the manual choke. I thought maybe the heat riser was to help heat the intake manifold so the auto choke would shut off quicker (since the coil is mounted to the intake manifold)? I don't plan on driving the truck as much when it gets colder anyway and it is always garaged at home, so I think I will just make it permanently open unless someone else chimes in with a reason why I shouldn't.

[Brad]

Like Palf said, you'll be fine without it but it'll take a bit longer to warm up the engine.
As far as wiring it open- you won't have to do anything. It will naturally hang in the open position. As long as it's not crusty and stuck and is freely moving, you'll be fine not using it.

[Stock72c10]

I am more wiring it to keep it in position, right now it is falling out and just the butterfly is holding it in (the counter weight is hanging about an inch from the manifold). This also most likely is causing some exhaust leakage as well. Thanks for the input.

[Luvlegs]

Originally Posted by Stock72c10

My manifold has all the parts for an automatic choke, but the PO said he couldn't get it to work correctly so he installed the manual choke. I thought maybe the heat riser was to help heat the intake manifold STILL DOESN'T MAKE SENSE TO ME BUT MINE IS THAT WAY ALSO so the auto choke would shut off quicker (since the coil is mounted to the intake manifold)? I don't plan on driving the truck as much when it gets colder anyway and it is always garaged at home, so I think I will just make it permanently open unless someone else chimes in with a reason why I shouldn't.

What is the counter weight you are refering to and how is it "just hanging"? And when you say butterfly, I assume you are refering to the one in the carb correct? I guess I just don't get the whole setup - I had a post awhile back with pics and noone could explain why the auto choke was mounted on the intake manifold - it kinda goes against reasoning... so far anyhow...

[Stock72c10]

I will take a picture tonight. There is a (what I call) butterfly valve in the inside of the header (kind of like the choke in the carb) that closes when it is cold to keep heat in the manifold and then as the it heats up a spring on the outside lets it open. There is a counter weight on the outside that helps keep it open. These are both mounted on a shaft that goes clear through the intake manifold, but on mine there isn't anything holding the back side in so it is just hanging with just the butterfly keeping it from coming all the way out. Here is a drawing looking down the exhaust manifold outlet (once again, I am not an artist).

[Palf70Step]

I do not know how much difference there is in the 72 vice 70 automatic choke on the 250, but you can have all the parts, but even when they were new the automatic (mechanical) chokes were know to be a pain in the *&^. Most of the time folks got tired of F'n with them and installed a manual choke. That is probably what your prior owner was talking about on the choke. I am keeping my 70 as a manual choke, even though I have the V8 now. I may convert to an electronic choke on the V8 later, but first I have to get all the pieces together to get it running again

[Stock72c10]

Here are a few pics:
1. This is how it is, notice how it is hanging out.
2. This is how it should be (I think), pushed in.
3. Quick fix, I couldn't get wire around the manifold so I put a glob of quick steel in front of it to hold it in place until I come up with something better.

I still don't know if it in the open or closed position, it seems to run okay. I am still looking online for a picture of it so I can be sure.

[Stock72c10]

I hate to continue to beat this horse, but does anyone have a 250ci straight six with a heat riser and, if so, is this the proper orientation for it to be in when open? Thanks for any help you can give.

[68gmsee]

I took a pic of mine. I usually disconnect it in the summer and rehook it back up in the winter.

It moves counterclockwise as it warms up and when I rev it up but mine doesn' go all the way down like yours. The pics show it cold at first and almost completely warm on the second pic.

I suspect yours is in the open position as it is. But if you're really worried about it, disconnect the exhaust pipe and look at it from the bottom.

[68gmsee]

Forgot to mention.

When I disconnect it, it falls downward counterclockwise. I'd say maybe 1/2 of the way from the uppermost position before it stops.

This is a replacement exhaust manfold. The original heatriser was gone like yours so I just replaced the manifold.

[Brad]

Originally Posted by Stock72c10

I hate to continue to beat this horse, but does anyone have a 250ci straight six with a heat riser and, if so, is this the proper orientation for it to be in when open? Thanks for any help you can give.

Yes, that's the proper orientation for it to be in when it's broken. I mentioned that in my previous post. GM designed it like that so it wouldn't block the exhaust when the spring broke. Like the last poster mentioned, if you don't believe us, just unhook the exhaust tube and look up there for yourself.

[Brad]

Originally Posted by 68gmsee

I took a pic of mine. I usually disconnect it in the summer and rehook it back up in the winter.

I don't see the point in doing this, any particular reason why you do it?

[Stock72c10]

My issue was that since the whole thing "sprung" out of position, I didn't know if it had jumped a stop or something. According to 68gmsee (thanks for the pics) it sounds like there is a stop that holds it horizontally (not at the bottom like it currently is on mine). My exhaust is old and rusty (per my pics) and it is not easy at all to "just unhook the exhaust." Once again, thanks for the help 68!

[Stock72c10]

Just for future generations, I found this picture online that shows the heat riser, it seems that the riser is only supposed to turn 90º. At straight up it lets exhaust get up to the intake manifold, and at 90º counterclockwise it shuttles air out the exhaust. I will break mine loose tonight and orient it to 9 o'clock.

[68gmsee]

Where did you find that picture? I remember I looked a couple years ago for a pic and never found one.

And yes, you are wise not to mess with the exhaust manifold bolts if you don't have to right now. I broke a bolt trying to remove the exhaust nut and damaged the hole when I drilled it out.

[Stock72c10]

I found it at Rockauto.com, just search for 72 c10 exhaust manifold.

[LeDevil]

Is my 327 supposed to have one of these because it has something very similar on the drivers side exhaust manifold. I don't mean to steal your thread I'm just curious

[Brad]

Just for the record, Stock72c10 I was wrong in what I said above regarding your heat riser weight and it's current position. I went out and checked tonight on an intact bare manifold I have and sure enough, it's exactly how 68gmsee described it! I'm sorry about the misinformation I gave you- that's a pet peeve of mine. I'll take some pics tomorrow of the butterfly and post them.

Now, I think your butterfly has broken away from the weight and it may very well be in the correct position for exhaust to exit but the only way to know for sure is to remove the exhaust pipe and check from below. I'm just wondering if you blindly secure the weight in the vertical position, will you know for sure that it's allowing exhaust to freely exit since the butterfly inside may still be partially closed? Because really, that's the main concern here, not the actual weight at this point. Since the weight and butterfly appeared separated, you could still have the weight glued like you have it as long as the butterfly is in the open position.

[newbraunie]

Originally Posted by Stock72c10

Here are a few pics:
1. This is how it is, notice how it is hanging out.
2. This is how it should be (I think), pushed in.
3. Quick fix, I couldn't get wire around the manifold so I put a glob of quick steel in front of it to hold it in place until I come up with something better.

I still don't know if it in the open or closed position, it seems to run okay. I am still looking online for a picture of it so I can be sure.

The pics shown here have it in the open position.

[newbraunie]

This thread has got me thinking about my setup. Here are pics of mine - 292 6cyl with butterfly held in closed position. My coil spring is long gone but the butterfly is in good shape. I recently did R&R on exhaust/intake gaskets and found that the PO put this Stanley L bracket on butterfly to hold it in closed position. I decided to leave it like this since I also have manual choke. My manual choke control (see pic) appears to be add on. I assume factory choke control would be on dash bezel although mine also has factory throttle control and I have never seen dash bezel with choke and throttle controls on it. This leads me to believe that my truck originally had auto choke. Is it possible that the butterfly did not work well to cycle auto choke off and PO installed manual choke? My SPID indicates oil bath air cleaner (also long gone) came with truck. I have seen many oil bath air cleaners for manual brakes and they do not have stove pipe assemblies. Maybe this lack of stovepipe assembly caused auto choke to not work properly? Maybe auto choke/oilbath ac was bad factory combo? I got the truck with aftermarket P.O.S#!@ air cleaner and have since replaced with factory offset air cleaner since I will be installing power brakes soon. The offset ac did not come with stove pipe so I am in the hunt for one and will probably go back to auto choke carb also. Didn't mean to ramble on with all these directions or grab the thread in the wrong direction!

[newbraunie]

Originally Posted by LeDevil

Is my 327 supposed to have one of these because it has something very similar on the drivers side exhaust manifold. I don't mean to steal your thread I'm just curious

On Inline 6 butterfly is above exhaust flow and does not restrict flow when open or closed, it only allows flow up to intake to heat it.

[Brad]

I hope this helps.