Heat Riser Removal

[Lunchbox]

What’s the best way to remove the heat riser from an 340 exhaust manifold? Currently it is seized closed can wiggle it slightly.

 

[Katfish]

Soak with PB Blaster and heat cycle it with a torch.
I cut mine out and tapped it for a bolts.
Not for the original guys, but my car is just a driver.

 

[Lunchbox]

Soak with PB Blaster and heat cycle it with a torch.
I cut mine out and tapped it for a bolts.
Not for the original guys, but my car is just a driver.

Worked like a charm! Had a hose clamp I put around the large diameter counterweight, allowed me to get a larger channel lock on it without messing it up. PB, heat, work it, repeat. Moves freely now.

Looking at the butterfly it appears to be welded to the shaft on the inside of the manifold. Thus the reason to cut it to remove it.

Is it safe to assume this isn’t needed for fair weather cars? Would like to remove the butterfly but still make it look stock on the outside.

 

[Katfish]

Yeah, that's probably what I should have done.
With a little patience, you should be able to cut away the butterfly and leave the shaft intact.

 

[Former owner]

Worked like a charm! Had a hose clamp I put around the large diameter counterweight, allowed me to get a larger channel lock on it without messing it up. PB, heat, work it, repeat. Moves freely now.

Looking at the butterfly it appears to be welded to the shaft on the inside of the manifold. Thus the reason to cut it to remove it.

Is it safe to assume this isn’t needed for fair weather cars? Would like to remove the butterfly but still make it look stock on the outside.

You really want to have it in good operating order. It is used to heat the choke. When the exhaust crossover stops, you will get an accumulation of crud, first in the heads, and then up into the manifold. Mine was rattling, so I just wired it open to stop the noise. Mine was a 71 Cuda 340 with manual transmission. Once the heat riser was disabled and the aforementioned buildup began, the choke remained partially closed after warmup. When the engine was shut off, I began to experience dieseling (after running) because the idle was set to spec (900 RPM). This was in sunny CA, BTW. So after pulling the heads and cleaning out the caked carbon from the passageways (and the mating passages on the intake manifold), I secured a heat riser repair kit manufactured by Everco, and fixed the heat riser. Everything returned to normal after that. Not sure if any of those kits are still out there, but I would absolutely try to fix that.

 

[Chryco Psycho]

Cut the plate out & leave the shaft

 

[Lunchbox]

Sounds like most people are saying that you don't need a functional heat riser with the exception of @Former owner. Any further explanation would help me, TIA.

 

[Ricks72Chlgr440]

Sounds like most people are saying that you don't need a functional heat riser with the exception of @Former owner. Any further explanation would help me, TIA.

Only relevant to need the heat riser if using the OE style carb with divorced choke (in manifold) in cold climates. Aftermarket carbs have electric chokes that are independent. Some later divorced chokes had electric assist elements too which would also negate the need for the riser and open crossover passages.

 

[Katfish]

Engineers have to design for the worst case scenario, Alaska cold to desert heat.
Riser is designed to make the engine heat up quicker, if you don't drive in cold weather, it's not needed.

 

[Former owner]

Sounds like most people are saying that you don't need a functional heat riser with the exception of @Former owner. Any further explanation would help me, TIA.

I respectfully suggest that Chrysler would not have installed it unless there was a need. There was. I detailed the issue I had as a result of a disabled heat riser. If you do many short trips, you can expect the same. The issue has to do with heating the choke coil, and getting the choke (and fast idle cam) completely off as quickly as possible. That is the sole function of the heat riser valve, and they were installed industry wide in USA.
If, for example you start up on a cool morning, and take a 5-10 mile run, the choke might not get completely heated without the heat riser in good working order. As a result, you will still be on a fast idle step when you shut off. This causes the engine to diesel when it shuts off, because the idle stop solenoid is not engaged. Accordingly, it will not return to curb idle (500 RPM in my Cuda) so it can shut off properly. There is a fuel economy element as well, but we've not touched on that. I am 51 years and counting into working in the auto industry. Best of luck with whatever you choose to do..

 

[Former owner]

Engineers have to design for the worst case scenario, Alaska cold to desert heat.
Riser is designed to make the engine heat up quicker, if you don't drive in cold weather, it's not needed.

I can assure you that it was needed in CA back in the 70-80s...