Need help with manifold heat riser?

[ricosan]

Good morning everyone

Yesterday I removed my exhaust/intake manifold from my straight eight. Fortunately there are no cracks in the top part of the exhaust manifold where it is attached to the engine but the flange that attaches to the exhaust pipe to the Manifold is in pretty poor shape. It is with the welder now.

My question is this. Should there be a gate of some sort here? What size should it be?:confused:

[GLong]

There usually would be a 'butterfly plate' on the shaft going across the opening, and some form of lever on the external part of the shaft to control the position of the butterfly plate.

A position of 'hot' would have the plate partially blocking the passageway, forcing exhaust gasses against the intake manifold surface.

An opposite position of 'cold' would have the butterfly plate blocking the intake from receiving hot exhaust and streamlining the passageway for the exhaust flow.

What car is this for ?? can you post a photos of the intake/exhaust together on the engine ?

Is there a dashboard control for manifold heat ?

Greg L.

[ricosan]

Hey Greg,

This is my '32 Marmon with the "big eight" engine.

The top of the shaft is connected to a cable on the dash and is manually operated. When I opened up the heat riser, I found only the shaft. I would like to have the butterfly plate fabricated and welded back to the rod. My problem is my butterfly plate was eaten up many years ago and there is no evidence of it left. When you pull the knob on the dash, the shaft is turned counter clockwise. Should it rest up against the right side toward the front of the engine and when opened to help with cold starting it would be perpendicular to the engine?

[ricosan]

Hey Greg,

This is my '32 Marmon with the "big eight" engine.

The top of the shaft is connected to a cable on the dash and is manually operated. When I opened up the heat riser, I found only the shaft. I would like to have the butterfly plate fabricated and welded back to the rod. My problem is my butterfly plate was eaten up many years ago and there is no evidence of it left. When you pull the knob on the dash, the shaft is turned counter clockwise. Should it rest up against the right side toward the front of the engine and when opened to help with cold starting it would be perpendicular to the engine?

[GLong]

Hi, nice car. You want the butterfly to be in the 'streamlined, no exhaust deflected' position when your button on the dash is in the full forward positon, which would be the 'cold' position in my thinking. I can's quite see enough to get the geometry right in my head, but if you use a piece of cardboard and a clip to hold it to the shaft, have someone operate the dashboard button, you will see what needs to be done..

I have no personal experience with this engine or car. But with our modern fuel, with or without ethanol, the engines do not need as much manifold heat as the old gasoline required. Many, if not most people will put a solid piece of 16 or 14 gauge stainless steel over the exhaust opening, between two gaskets and let only the amount of heat that is conducted by contact between the manifolds be the source of intake manifold heat. This keeps the carb cooler, and a denser charge of air/fuel to the engine.

I have done this to several cars over the years. and the only difference I've noticed is the engine likes to run with a bit of choke for about one or two minutes longer than without the exhaust-heat blocking plate. The engine runs better warm, and carb fuel bowl boiling is reduced or eliminated.

Greg L

[nickelroadster]

I would take the suggestion of using a piece of cardboard to try and figure out the geometry of the system. I would think that the best way to do this would be to make it so that you have to pull against the flow when you close it to get heat. If something goes wrong, you want it to try to open. Think about the system in operation and the direction of airflow and try to figure out. Remember ,you are probably not going to operate the car in cold weather and it is probable that you don't really need it.

[ricosan]

Good morning Guys,

Thanks for the help.

It's certainly tempting to just replace the rod and forget the butterfly plate. But I hate to have a button on the dash that is inoperable - does nothing. Then again I'm afraid to put a plate that may interfere with smooth operation. That said it looks like when the plate is closed (dash button pushed completely in) it should have the plate turned to the right toward the front of the engine where it would rest during normal operation. A cardboard template here would help with getting the right shape. Pulling the knob out will bring the plate back toward the rear of the engine turning it in a counter clockwise direction. The plate can't be very large since the rod is offset to the right, making this a shorter distance to the edge of the heat riser chamber. This looks to be about 1" mol. When the knob on the dash is pulled out this 1" plate would be perpendicular to the engine.

I think I had better visit the welder before he tackles the project so that we can both be sure that it will work when reinstalled.

ricosan

[paulrhd29nz]

What does the top side of your heat risser look like?

[Bhigdog]

Good morning Guys,

Thanks for the help.

It's certainly tempting to just replace the rod and forget the butterfly plate. But I hate to have a button on the dash that is inoperable - does nothing. Then again I'm afraid to put a plate that may interfere with smooth operation. That said it looks like when the plate is closed (dash button pushed completely in) it should have the plate turned to the right toward the front of the engine where it would rest during normal operation. A cardboard template here would help with getting the right shape. Pulling the knob out will bring the plate back toward the rear of the engine turning it in a counter clockwise direction. The plate can't be very large since the rod is offset to the right, making this a shorter distance to the edge of the heat riser chamber. This looks to be about 1" mol. When the knob on the dash is pulled out this 1" plate would be perpendicular to the engine.

I think I had better visit the welder before he tackles the project so that we can both be sure that it will work when reinstalled.

ricosan

What you say sounds perfectly logical. If it were me I would fabricate a new rod and baffle using stainless steel. The baffle should have generous clearance within the manifold.............Bob

[GLong]

No question that having the car 'right' and 'as original' is a good thing, and a good feeling.

When you get the plate mockup made, you will see, that because of the offset of the shaft, that there is no way to keep all the exhaust away from the intake manifold, even in the full 'cold' position. There will be some intake surface area exposed to the hot exhaust.. The plate just directs a lot more of the hot exhaust at the intake when in the 'hot' position.

The reason I recommend the plate is that our old car's engine compartments are hot by today's standards. The air coming through the radiator is heated to 160-180*, and this doesn't keep the items in the engine bay very cool..

Pop open the hood after a nice long run in 80* + temps when the engine has been working and the water temp has climbed a bit.. and carefully touch items like the air cleaner, the firewall, the hood and hood stay, that stuff is HOT.

Our ethanol fuel boils at somewhere around 170-180* and causes us much grief with vapor lock, cars that won't idle hot, won't start hot etc because the fuel is boiling.

Especially with downdraft carbs, sitting on top of a hot intake manifold, they boil their float bowls dry in about 5-10 minutes on a hot day, when parked while the driver gets lunch, runs errands etc. Then the driver HAS to have an electric pump to prime the carb, or the engine will take a long time to pump fuel to the carb with the mechanical pump. if at all.

So the plate to block off the direct exhaust gas contact to the intake came to be..

I think if a person was able to always have ethanol free fuel, we'd be OK, but I've seen one tank of ethanol free work wonderfully, then the next tank of gas, with ethanol, only a mile down the road, and the electric pump back at the fuel tank is REQUIRED to keep fuel headed forward to the engine .

If your Marmon is an updraft setup, I'm not sure the block off plate is as effective as with a downdraft setup.

Greg L

Edited January 14, 2014 by GLong (see edit history)

[Curti]

there is no way to keep all the exhaust away from the intake manifold, even in the full 'cold' position. There will be some intake surface area exposed to the hot exhaust.. The plate just directs a lot more of the hot exhaust at the intake when in the 'hot' position.

I have been under the impression that the purpose of a 'heat riser' is to direct the hot exhaust gas in the direction of the intake manifold on cold start up's. As the engine warms up, the heat riser levels out and directs the hot exhaust straight threw the manifold.

[GLong]

Hi curti, you are correct. But what needs to be commented on is that not ALL the exhaust is directed against the intake manifold, and when hot, while the heat riser butterfly valve is no longer 'directing' the flow toward the intake, it is really only not blocking the normal flow down the exhaust manifold.

The butterfly valve or flapper is not a sealed valve, it is more of vane, stuck in the exhaust flow, to direct or re-aim the flow. Hot exhaust gasses are not kept away from the intake when the flapper is in the hot postion, the hot gasses are just not directed to hit the intake on the way out of the exhaust manifold.

Trying to describe this rather than showing it with a drawing or a good photo is frustrating. On a '50's or '60's V8 engine, at least the ones I've looked at, the heat riser butterfly is capable of almost blocking all the exhaust flow. But on the old inline engines, the butterly is more of a gate in a garden fence. the flapper is on one side of the pivot shaft, not equal on both sides. So even when 'closed' or hot position, the intake manifold is heated quite a bit..

I'll try to get a photo of one of the heat riser butterfly valves on a Pierce inline 6 engine, i'm up to my ears in projects so this may not happen today.

Greg L

[Curti]

Hi Greg: I completely agree! I never want to tell some one they are wrong on a given subject, because quite often it turns out that I am am the one in error.

My experience with them is to the degree of re-bushing the shafts and general repair. I work on mid 30's Auburn's which have a bimetallic spring which contracts when hot to open the gate.

I garner from this post that Marmon has some kind of manual heat riser control of which I am totally unfamiliar. If the OP is going to fabricate one he really needs a pattern from an original.

If it is like Auburn the valve is not a plate but has a curve on one edge to capture additional exhaust.