Heat riser (1 Viewer)

[Alstruck]

I just found on my recently acquired 1971 FJ40 the heat riser cover and bimetal control are missing. Also the rod is missing. I don't know if it was removed or if it rotted away. If the rod rotted away, then what happened to the butterfly? My question is, has anyone run their truck without the heat riser. I know it's purpose, but I'm in FL so the cold is not an issue. But you have constant heat on the intake manifold.
Also if you do remove the hear riser. How do you close the holes where the rod was?
Thanks
Rick


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8

 

[Cleg]

On my 72 the bimetal coiled strip was gone and what was left of the shaft was fused to the manifold with rust. I suspect that very few of these assemblies are still functioning the way they were intended to.
Many of the F exhaust manifolds developed cracks. I have heard this attributed to overheating.

It sounds like someone removed the butterfly valve & rod from yours while the manifold was off or at least when the down pipe was off because there would be no way to pull the shaft out with any remnant of the butterfly attached.
If you just need to plug the holes, you could just run a bolt through and out the other side.

My original manifold had cracks and I located a replacement. The butterfly in it was also a rusted mess. I did not want to take the risk of cracking the replacement so drilled the shaft out and built a new valve assembly out of stainless.

The original butterfly served as a pattern for the new one. It is attached to the shaft with 2 stainless screws in tapped holes, ends peened so it doesn't get loose with repeated cooking in the exhaust. The shaft was modeled after what was left of the original & has the counter weight attached but no bi-metal actuator.
It has a sheet metal tab screwed to where the actuator went to hold the valve in the closed position.
If I ever locate an actuator it should work.

 

[Alstruck]

Can you get to the butterfly if the carb is removed? I guess I could make a butterfly out if stainless also.
I'm guessing that you keep your butterfly closed, that means the exhaust is directed to the exhaust pipe instead of towards the intake manifold.
Thanks for your reply
Rick


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8

 

[Cleg]

heat riser valve

There is no access through the intake manifold.
The base of the intake manifold is solid and the butterfly simply exposes the underside of it more directly to the exhaust gasses.
The intake & exhaust manifolds have to be separated to get to the valve because the diameter at the down pipe is smaller than the butterfly.

Fit of the butterfly in the exhaust manifold does not have to be very precise.
I used the old flapper as a pattern and may be able to locate it if needed for dimensions.

I saved some of the panels from a stainless steel gas grill instead of hauling them to the landfill. It has been an excellent source of sheet stainless for the occasional bracket and for applications like this.

Notice the hairline crack in the left branch of the exhaust manifold.

 

[Alstruck]

Thanks for the pics. Of course HD intake manifold is solid. Not sure what I was thinking.
I do see the hairline crack. I'm going to run a bolt through the exhaust manifold to close the rod holes. I have an exhaust leak but I'm not sure if it's the manifold or the exhaust system. I'll work on that today and figure that out.
I of notice when I start the truck. After a few minutes of heating up it start to run a little rough and which I think is caused by the lack of the butterfly in the exhaust manifold causing the intake manifold to get too hot. So I've got to do something to close off that heat source. Does that sound right?


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8

 

[Cleg]

Mine was all apart during the rebuild so I took the time to make a functional heat riser valve, that is, if I ever add the actuator.

It is a big job to take it all apart so plugging the hole with a bolt makes sense until you have everything else worked out.

I never ran with the butterfly missing so don't know what the effect is of having the extra heat all of the time.

 

[Alstruck]

Thanks for the help. I'm going to put a bolt through the holes and see how it runs with no butterfly. I'll let you know.


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8

 

[sggoat]

Running rough after warm up may be a sign of a vacuum leak at the intake manifold. Get it hot then, spray some carb cleaner around the area-if the engine suddenly revs up--you have a leak.

 

[Alstruck]

Thanks sggoat. I'll give that a try.


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8

 

[Alstruck]

While putting a bolt into the exhaust manifold. I realized on the back side of the manifold was the heat riser shaft and counter weight. That tells me the butterfly is probably still inside the manifold or is rotted and is gone. So I guess if I can find a butterfly and bi-metal heat controller. I could put this thing back together.


1971 FJ40
1952 VW Split Bug
1997 Jaguar XK8