Exhaust and Intake Manifold Decking

[Bud]

Does anyone near the Dayton, OH (or maybe 50 miles north of Dayton) have a FIXTURE (picture 1) to mill or plane the intake/exhaust assembly so it is flat within .0025" but also square to the carburetor flange? I don't want a shop that uses a head planer (freehand--picture 2 ) or a belt sander. Please see the thread by JackA from 12-03-2013 on Fordbarn.

I am examining brand new manifolds.

The intake manifold is low on both ports toward the middle by .007". The intake ports are also not flat R-L by .0065 on one port and .0060 on the other port.

Laying the exhaust manifold on my surface plate indicates the gap at the #4 port ranges from zero to .003 loose; at #3 port, zero to .0045 loose; at #3 port, zero to .0045 loose; at the #1 por, .0035 to .0070 loose.

What flatness tolerance did Ford require on the engineering prints for the intake and exhaust manifolds?

 

[chrs1961815]

Are you using both new manifolds, originals, or one of each? Didn't wuitr understand what. I will say those measurements you have are almost certainly way too small to cause any leaks or issues. For what it is worth, Ford's tolerances for that definetely did not go that many decimal points!!! I have gotten away with a lot worse than I should have.

 

[nkaminar]

Any good machine shop can setup the manifolds on a mill with some adjustable blocks to get them in the right position and perpendicular to the carburetor flange. They can then surface the manifolds with a fly cutter.

For those who want to do the surfacing themselves, you can glue some good 40 grit sandpaper to a surface plate or any good flat surface and sand the manifolds until they are flat and parallel. That is what I did. I used the sandpaper available from automotive paint supply houses that has a sticky back surface and mounted it to a flat piece of granite. The sand paper is normally attached to a sanding block.

 

[Bud]

nkaminar, I have successfully done what you describe (sanding) on smaller parts. I have a surface plate but it is fairly small and the exhaust manifold barely fits on the diagonal. But I may try it.

Getting a machine shop to mill the manifolds is possible, but I have found getting them to want to do it and do it right is another thing.

Thanks.

 

[Bud]

By the way, I am looking at brand new intake and exhaust manifolds.

 

[BRENT in 10-uh-C]

Any good machine shop can setup the manifolds on a mill with some adjustable blocks to get them in the right position and perpendicular to the carburetor flange.

Neil, unfortunately your comment is very misleading and IMHO is not an accurate statement. A set of blocks as you are suggesting do/will not work because you have nothing to reference off of unless you are using stands to support the manifolds to a uniform height throughout the entire length. Even a set of 1-2-3 blocks will not fit into that area where the spot facing is.

Unless someone has ever tried to do this, I doubt they realize the complexity of the fixturing, -AND the flexibility of a cast iron manifold set that is only attached by two fasteners on each side of the draw tube. The flanges of each manifold need to be nearly parallel so the clamp can place equal force as it bridges the two opposing flanges.

I am enclosing two pictures of my fixture that shows how the manifolds are supported against the factory spot-faced areas where the studs protrude. The height of these risers must be precise and all be equal in length. I can provide additional photos of my jig if anyone wants to replicate it however it is a complex fixture that requires some fairly precise machine work to make the fixture in an effort to achieve an accurate cut within factory specs.



To add a FWIW and to confirm why Bud is asking this, using a belt sander or rotary surfacer is a great way to get the angle of the carburetor canted off center in relation to the engine. At that point, question yourself whether this affects float levels.

.

 

[nkaminar]

Brent, Your fixturing is in line with what I had in mind. It is not easy to do with a set of blocks, and adjustable risers but possible. I have set up more complicated shapes on my mill. How do you know that the intake and exhaust manifolds of possible mixed vintage and prior use have parallel and the same factory spot faced heights? The washers that Ford used are designed to accommodate different spot face heights.

Sanding the surfaces is not the ideal method but works if careful and not too far out of wack. Machining is the best method but not always available.

I know you always have the best equipment and methods, but not everyone is as well equipped as you are.

By the way, the intake manifold in your photos is the wrong color. (Humor)

 

[BRENT in 10-uh-C]

Brent, Your fixturing is in line with what I had in mind. It is not easy to do with a set of blocks, and adjustable risers but possible. I have set up more complicated shapes on my mill. How do you know that the intake and exhaust manifolds of possible mixed vintage and prior use have parallel and the same factory spot faced heights? The washers that Ford used are designed to accommodate different spot face heights.

Sanding the surfaces is not the ideal method but works if careful and not too far out of wack. Machining is the best method but not always available.

I know you always have the best equipment and methods, but not everyone is as well equipped as you are.

To answer your first question, it does not matter if the manifolds have been mixed/matched. And, it doesn't even matter if the thickness' of the manifold flanges are of different measurements between the manifolds. Often times, this is the case due to previous 'mechanics'. The spot facing will become the new datum for proper alignment, ...so once fixtured properly and the manifolds have been flycut, all six port flanges will now be the same thickness and in the same plane.


It is not about having the best equipment, ...it is about doing the job properly. Using blocks on a Mill that does not have the ability to machine the flanges to be the same thickness' nor make the flange surface be perpendicular to the carburetor mounting flange only takes a poor quality piece and makes it into another poor quality piece. Remember, our job as Restorers and Caretakers is to correct the issues caused by previous mechanics, -which often times includes 'restorers' from a former time. So with that understood, often times there are certain jobs when doing proper restoration or repair work on a Model-A that require machines & fixtures that are outside the scope or abilities of what the home Restorer may have at his disposal. It is in those times, the Restorer/Repairer needs to find an experienced shop that is capable of doing the job correctly for them.

 

[40 Deluxe]

To add a FWIW and to confirm why Bud is asking this, using a belt sander or rotary surfacer is a great way to get the angle of the carburetor canted off center in relation to the engine. At that point, question yourself whether this affects float levels.

.

I wonder if it's possible to "get the angle of the carburetor canted off center" enough to affect the float level to a measurable degree? The purpose of resurfacing is to get a flat surface so that each port will seal to the block. If the carb is canted a few tenths of a degree as a result, will it even be noticeable? Will the carb be sitting perfectly level in real life? Not very often! Most roads have a crowned surface, so your A usually leans slightly to the right. And most roads go up and down hill to a noticeable degree. What does that do to the float level?

 

[Keith True]

The machine shop I've been using for most of my tractor/equipment work for 40 + years was telling me about some of the requests he gets for that kind of work.A lot of folks get to reading stuff on the internet,and think they have to do things a certain way to get things done.He will set up and mill a set of manifolds any way you you want them done.You will just pay the $85. hourly rate instead of the flat $50.he gets to skim them off on his sander bench.He said he doesn't want to make up a jig to set up in his machine for 25 or so manifolds a year.Especially with the vast majority of them for guys like me that just want them true.He said he has a few over the years where the angle was off a mile,enough to upset the angle of the exhaust pipe.He said those were ones that got faced off by kids in high school shop.A little is good,more is better.

 

[BRENT in 10-uh-C]

I wonder if it's possible to "get the angle of the carburetor canted off center" enough to affect the float level to a measurable degree? The purpose of resurfacing is to get a flat surface so that each port will seal to the block. If the carb is canted a few tenths of a degree as a result, will it even be noticeable? Will the carb be sitting perfectly level in real life? Not very often! Most roads have a crowned surface, so your A usually leans slightly to the right. And most roads go up and down hill to a noticeable degree. What does that do to the float level?

Good question and food for thought. A couple of tenths, ...likely not.

 

[nkaminar]

Weber says that their carburetor should be level but the manifold made for the Model A does not compensate for the 2 degrees or so that the engine is slanted at. In practice it does not seem to matter. Accelerating or braking or turning corners the gasoline is sloshing around anyway. I set up the float a couple mm lower so to compensate for the slope but, like I said, it does not seem to matter.

If the manifold is not machined properly, meaning perpendicular to the carburetor flange, then, depending on how bad it is, the exhaust pipe may not line up and it may effect the carburetor performance, maybe making the float stick. The test would be to park the car on a sideways slope and see how it runs. Nothing like data to take the guess work out of the equation.

 

[Bud]

On my first post I edited it and added the dimensions of the manifolds and where the low spots are.

 

[Bud]

The vendor whom I purchased my manifolds said each manifold, intake and exhaust, should have a total tolerance of .005" on the dimension between the common mounting surface and the port face. So I interpret that to mean that the total variation acceptable would be .010", manifold to manifold. He stated that was based on the Ford details. I have not seen the Ford details, so I have to accept this as correct.

 

[BRENT in 10-uh-C]

The vendor whom I purchased my manifolds said each manifold, intake and exhaust, should have a total tolerance of .005" on the dimension between the common mounting surface and the port face. So I interpret that to mean that the total variation acceptable would be .010", manifold to manifold. He stated that was based on the Ford details. I have not seen the Ford details, so I have to accept this as correct.

Bud, I am not sure I totally agree with that statement. I am unaware of an assembly drawing for the A-9425 Manifold and the A-9430 Manifold parts. The parts books do not reference this nor do I find anything at MAFFI.

Each one of those drawings (-the 9425 & 9430) will have finished machine specifications for the flange areas listed. I would agree there was likely an 0.005"± specification given on the print as the maximum allowable tolerance, -however since these flanges would be attached to a fixed plane (-this being the side of the engine block), the maximum deviation would only be 0.005" total. To put this into perspective for everyone, a Human hair is generally measured as 0.002"-0.003" thick. Therefore the maximum tolerance that Ford's engineers specified would have been about the thickness of 2 Human hairs, -or less.