Exhaust Manifold Inspection Guide

[BillCNC]

Hey Guy's

We had a Paradise Valley Model A Ford Club (PVMAFC) meeting last night and I wanted to share with you a fantastic write-up in our newsletter "The Steering Column". The article discusses how to correctly inspect your exhaust manifold, all the problem issues that arise and how to avoid them. I thought maybe it could benefit others as well.

I don't know how to strip the article out of the newsletter so I'm posting the entire newsletter, it's small (5. MB) and the article your looking for is on page 7.

Hope you enjoy

Regards
Bill

[JDupuis]

Good article Bill: well written. Although not original equipment I've often thought of putting a flex pipe in the exhaust system approximately 3" to 5" below the manifold. Just my thought on this problem. Thanks for posting. Jeff

[BILL WILLIAMSON]

I've "thought" about a flat iron "bracket", welded to the head pipe & extending to a manifold stud, to prevent Manifold Sagging. The front end of the exhaust system is QUITE HEAVY.
Bill Dreamer

[BillCNC]

Thanks Guy's but it wan't written by me, ... had it been, you'd prolly need a 3rd grader to read it to you.

Yup, ... Lot's of info I didn't even think about. I sure got a ton of info out of it, like the weight of the muffler dragging the back corner down. I would have thought the manifold was more than strong enough for that to not even be considered.

Regards
Bill

[SeaSlugs]

Originally Posted by BILL WILLIAMSON

I've "thought" about a flat iron "bracket", welded to the head pipe & extending to a manifold stud, to prevent Manifold Sagging. The front end of the exhaust system is QUITE HEAVY.
Bill Dreamer

this is the reason the waffle/heater manifolds are hardly ever drooped they got extra meat on top preventing the ends from drooping.

Also if you use the gland rings as ford did it cant droop - surprised theres no mention of them in the article. The 4 mounting points now becomes 8 mounting points.

Yes the exhaust has to be able to free float so to speak and really should have another bracket in front of the muffler to take the weight off the manifold connection.

[160B]

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I printed page 7 and then scanned it as editable text, (OCR) and then copied and pasted the article to this post. It is attached as a pdf document so you can save it to your computer and or print it to share with others.

Exhaust Manifold

The early style Model A manifold used from 1928 to 1931 has a round outlet cross section. This first style is the A-9430 used for 1928-31 Model A's. The outlet on this manifold points primarily downward, not rearward.

In late 1931 the A-9430 manifold had a reinforced teardrop shape cross section of the outlet behind the number 4 mounting stud. This design was also used on 1933-34 four cylinder passenger and truck.

Original Ford exhaust manifolds have the casting pattern number located on the outboard side

The 1933-34 Model 40/46 four cylinder cars and commercial exhaust manifold 46-9430 is the same as the Model A manifold, but with the 46-9430 part number cast in the visible surface.

It was Ford's typical practice in that era to renumber parts with the latest production usage prefix though there was no actual change to the part itself. The Model 46 manifold 46-9430 was just a reincarnation of the last production design Model A exhaust manifold with no change other than part number prefix.

Exhaust Manifold Warpage

Model A exhaust manifolds are well known for warpage and sealing problems. The basic manifold design has a couple of shortcomings which lead to problems. First, there are only four attaching studs and there are no attainments at the front or rear extremes of the
manifold.

This bolt pattern allows an uneven clamp load which can allow leakage at the unclamped ends, as well as differential movement to the block with manifold expansion and contraction during temperature changes.

Second, the exhaust outlet is located at the far rear rather than at or near the center of the manifold.

The position of the outlet at the rear means that all four cylinders' exhaust heat is transferred and saturated at the rear port area. In contrast, the area at the number one port 'benefits' from cooling air from the radiator fan and the heat from only the number one cylinder.

This uneven distribution of heat along the manifold, combined with a less than ideal attachment pattern, allows the manifold to expand and contract unevenly during heating and cooling cycles.

Additionally, the weight of the muffler is suspended from the rear of the manifold, and adds an ever-present downward force on the hottest portion of the manifold.

Now just for fun throw in the fact that a great many Model A's also do not have proper ignition timing, and owners like to idle them at very low rpm's and tend to drive with the, spark too far retarded.

This late timing condition causes fuel to continue burning and releasing heat after passing into the exhaust manifold. This adds tremendous heat energy into the casting and actually can make the casting glow red hot as many people have experienced.

As the droop or sag at the number 4 port on a Model A manifold. The first three ports remain in line, but the number 4 port has dropped significantly.

This type of warpage is the primary failure. Manifolds do not seem to change shape or warp in the machined gasket surface plane. Re-surface the gasket surface is really of no value in addressing the typical warped manifold.

The up/down alignment of the four ports is really the concern. Typically the first three ports remain in a straight line, and the fourth port drops 1/8 inch or more.

If the port drops 1/8 inch then it is very difficult to align and seal the manifold and gasket to the engine block. The likelihood of an exhaust leak is very high.

Sag of the rear port by more than 1/8 inch is a good signal to start looking for a replacement manifold, or be prepared to deal with exhaust leaks at that area.

Muffler Tail Pipe Clamp
Have you ever wondered why the exhaust manifold on a Model A becomes distorted and leaks after years of operation-why the outlet of the manifold is no longer vertical? That condition is not normal; manifolds were not always that way.

There is a reason for this and it is not just because of continuous heating and cooling. Many people installing the muffler will tighten the clamp bolt where it fastens the muffler/tail pipe to the frame,
obviously to keep it from rattling.

This bolt is supposed to be little more than hand tight. That is the reason for the castellated nut and cotter pin- so that the bolt will not become un-screwed and fall off. The reason for this is to allow the tail pipe to slide forward and backward when the exhaust. system is heated and cooled alternatively. If the clamp is over-tightened the exhaust manifold actually bends when the muffler expands.

Yes, cast iron will 'bend' under these conditions. So remember, do not over-tighten, your muffler/tail pipe clamp.

[BillCNC]

Thank You 160B, ...

Regards
Bill

[Synchro909]

Not a bad article but it shows the usual disregard for RHD cars. The author suggests that it would have been better for Ford to have the exhaust gasses to exit the manifold near the middle. That can't be done! There's a thing called a steering box right there!!. What could have been done is to have the exhaust gasses flowing forward, then down in the vicinity of the timing gear cover to connect to an engine pipe and muffler. That would also mean that the hottest part of the manifold would have benefited from the air flow from the fan as the article points out now only benefits the front. That would have stopped the sagging problem right there.
Such an arrangement would also get the hot pipe away from he driver's feet. The hot air coming up through the gaps around the steering column and pedals makes these an unpleasant car to drive in hot conditions. The sometimes red hot exhaust goes between the clutch and brake pedals and the clutch pedal goes between the exhaust clamp and the engine block when depressed. The clamp has to be positioned just right if you want to be able to press the clutch.
I mustn't rant too much about the design shortcomings of these cars or I will be asking myself why I drive one!