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

Hey guys,

It's been a while since I've been around, but I got a questions for you. I've been working on my exhaust manifold, which had a locked-up heat riser flap. I had to mangle the end of shaft pretty well to get it un-seized and managed to break the welds that hold the flap to the shaft. So now I'm considering replacing the shaft, because I'm anal retentive. So here's the question part. Can I use a regular mild steel shaft, or should I use some type of hardened steel because of it's exposure to the heat/cooling cycles. I think expansion/contraction should be considered...don't want it to warm up, expand and seize in the hole.
Thanks guys

You can get replacement shafts but they are a bit pricey for what you get. Denny Graham tacked that issue a while back but I don't remember what he did of even if he said. I think he was going to make one so you might PM him & see how his turned out.

Just took a junker apart for show-n-tell Richard. I didn't replace the one that was in the junker. We were discussing the slit and how brittle it was. It might be a butch to make unless you were a machinist.
In answer to your question, sure you could just use a piece of mild steel round stock. Ya gotta get the timing right on the slot and need to weld the butterfly to the shaft, which you know since you say you broke the welds loose on the old one.
Denny Graham
Sandwich, IL

Tiny do you know where the replacements are availiable from?

I'm trying to get a consensus. Mine looks as if the flat side of the counter-weight is perpendicular to the direction that the butterfly flap runs, I forget at what angle the slit in the end for the spring is..... I'll look at it tonight and report back.

you could just remove the sleeves that are there drill the holes out install a helicoil and plug the thing up. no more stuck open or closed, no welding no wondering if you have it timed right and no puff puff puff when the shaft wears out again. that what i did on my three trucks with no issues.

Brian, here are a couple of pictures that show the orientation of the butterfly to the counter weight, that's the most critical issues. That’s where the pre-made shaft takes the lead, that is if they got the hole for the counter weight drilled in the right place. The slot is not terribly important as you can tighten or loosen the tension till you get the balance correct.
Just click the photo to enlarge it and the previous page has a few pixs also: http://www.pbase.com/dennygraham/under_hood&page=4

Not to put anyone down, but I personally would run a heat riser, why would the engineers have included them for three quarters of a century if they weren't necessary? Of course that has a lot to do with just what sort of performance your expecting from your engine.
Denny Graham
Sandwich, IL

Up here in the great white north... Well, its damp and green where I live...
I found that when driving the truck in cold weather, the heat riser valve doesn't just open when the manifold heats up. It opens and closes, depending on the temperature of the bimetallic spring right? I found that often, when pulling into stop and go traffic, where there were periods of idle, it would begin to heat the manifold again, if the temperature under the hood began to drop. Same thing when it was really windy. In fact, when windy and cold, sometimes it stayed on heat all the time.
I guess it depends on where you live, and what kind of driving you do. With a functioning heat riser valve, even if you live somewhere warm, you get a much faster warm up, with less stumble.

Plus, I always loved that after I shut the truck off and I was standing near it, I would hear the valve click back over to heat.

Just my two cents.

Thanks for all the input guys. I'm with Dehhy Graham and Mr. Lang on this one... If it wasn't necessary, they wouldn't have had it, especially considering how utilitarian our trucks are.

I have been suffering with a low RPM acceleration stumble on my truck.... (the flap was seized in the off-heat position). So a long warm-up time might account for some of my problems, since I have only taken it on very short drives so far (don't trust it much yet).

I can always count on the stovebolt!