Manifold gasket hole size
 

I just bought my first Model A. I cleaned out the carburetor and flowed the jets. Even with an idle jet that is large (68 ml/min), the engine was idling lean (around 450 rpm) even with the idle mixture screw all the way in.

After some messing around, I found the intake manifold gasket was leaking at the rear intake port. After disassembly I discovered the manifold gaskets ('31 style - copper with slots for the bolts) were in good shape but sat just a little off center. The holes in the gaskets for the intake ports are significantly larger than the passages in the manifold. With the gasket sitting just a little low (maybe 30 to 50 thousands), the hole in the gasket was right at the outer edge of the intake port of the manifold. This apparently allowed for a small air leak.

Are the intake holes in all the gaskets larger than the intake passages? Or do I need a different gasket?

Note 1: I have a Model B intake manifold on a Model A block if that is significant.

Note 2: By carefully centering the gasket as I installed the manifolds, I think I solved the leak. But I'd feel better if the gasket was not so close to the edge.

Note 3: I did put a straight edge across the manifolds, and all 6 ports seem to be flat and in alignment.

Re: Manifold gasket hole size
 

If you install gland rings on the exhaust ports then that will hold the gasket in the proper position when you install the manifold.

Re: Manifold gasket hole size
 

Thanks Jay, that's what I'm missing. Being new to Model A's, I had no idea there were gland rings. I guess I need to get a repair manual. 🥴

That brings up a follow-up question: When I look at the gland rings on Mike's, it says "For NEW Exhaust only". Any idea why it would say for NEW only?

Re: Manifold gasket hole size
 

The majority of original exhaust manifolds have a "drooping" port on cylinder 4, causing them to fail to line up properly with the block. Sometimes these can still be used, if the gasket is strong, but gland rings won't work because the counterbores are no longer aligned.

If your manifold still has all six ports exactly aligned, gland rings should work for you unless your engine is one of the very small number not produced with counterbores in the exhaust.

Re: Manifold gasket hole size
 

i use the red permatex sealer on exhaust ports both side of copper gasket.

Re: Manifold gasket hole size
 

Alex pegged it re: drooping manifolds. Easiest way to check would be to trial fit the exhaust manifold with gland rings but without the gasket. It will either go or it won't go. Depending upon the amount of droop sometimes you can get #1, #2 and #3 to fit in but #4 won't. At least that way you know the front gasket is liked up properly.


Of course, the ultimate solution is a new exhaust manifold. You get the benefit of a well machined surface to mate the exhaust pipe to. I've had to replace exhaust manifolds in both of my Town Sedans.

Re: Manifold gasket hole size
 

Do not use gland rings. Use Snyder's A9433 copper gasket set which have holes that mate exactly with the 4 manifold studs. This gasket provides instant alignment. The gasket with the slots requires manually aligning the gasket for proper sealing which doesn't always work. Gland rings can prevent the manifold from properly sealing. If the counterbored holes in the block and manifold are not deep enough the gland ring can restrict the gasket compression needed to achieve proper sealing.

Re: Manifold gasket hole size
 

Thanks for the explanation alexiskai. I'll check my exhaust manifold. I noticed the counterbores in the exhaust ports, but I didn't know why they were there. I suppose if it is out of alignment, I could always re-counterbore the number 4 port. But I'll probably just go with the gasket CT Jack recommended.

Re: Manifold gasket hole size
 

The manifold droops, NOT the block

Re: Manifold gasket hole size
 

The #4 manifold port cannot move independently from the other 3 ports. Yes, the entire manifold can rotate if not properly fastened.
Droop in my view is primarily the result of the manifold not being properly torqued. I cold check the 45#-ft torque on the manifold studs at least twice a year.

Re: Manifold gasket hole size
 

Drop of the exhaust manifold occurs from the weight of the muffler assembly repeatedly pulling downward on a very hot exhaust manifold. The thick conical washers under the manifold attachment nuts allow the manifold and studs to expand when hot, so overly to tightening the nuts flattens the washers and defeats their purpose. The gland rings protect the copper type manifold gaskets, but are not necessary if the gasket is steel.

Re: Manifold gasket hole size
 

Actually #4 port does move independently of other 3 ports.

Over MANY years the weight of the muffler pulls down on manifold.

The problem is made worse if someone drives the car with the spark retarded.

Retarded spark makes the rear of exhaust manifold glow red hot which makes cast iron soft then weight of muffler bends port # 4 downward.

If you do believe me, drive the car with spark retarded at night AND with the initial spark timing retarded then open hood and see the glowing cast iron in the dark.

Retarded spark is common when people drive with spark lever in wrong position and timing adjusted wrong.

Another reason for retarded timing is when folks think that they can find top dead center by sticking a wire in sparkplug hole or looking into sparkplug hole or using the thumb over the plug hole trick.

These methods will be are not an accurate method of finding top dead center.

Ford added extra cast iron at rear of manifold sometime in 30 or 31.

Re: Manifold gasket hole size
 

Just to reiterate what Bob said, the purpose of the rings is to protect the gasket material from being eroded by hot exhaust gases, NOT to support the manifold. They may have that effect to some degree but that's not why you would or wouldn't use them.

Re: Manifold gasket hole size
 

I believe the gland rings are there to prevent or to slow the sagging between #3 & #4. I never leave home without them. They have their purpose as stated above.

Regards
Bill