Intake manifold rotted out?

[Don]

Is there a quick way to check if your manifold might be bad? A friend 41 doesn't seem to want to run the way it should,changed carb ,Dist,coil & cond,..did have low voltage at the coil about 3 volts when starting,it is hard to start .does not idle smooth and has no power on the road.Tks..

[Kube]

Originally Posted by Don

Is there a quick way to check if your manifold might be bad? A friend 41 doesn't seem to want to run the way it should,changed carb ,Dist,coil & cond,..did have low voltage at the coil about 3 volts when starting,it is hard to start .does not idle smooth and has no power on the road.Tks..

Don, I have NEVER seen an intake "go bad". I suppose it's possible to "rot out" if it were laying in mud for a period of time. Otherwise, it's a heavy cast iron piece. Little can "go bad".
You can spray carburetor cleaner on it and at the gasket edges when the engine is running to check for leaks. If the idle changes, you've got a leak.
From your description of ailments, it sounds like carb. and / or ignition issues. If you do not have the proper test equipement, I might suggest swapping ONE piece at a time (carb., distributor, condenser, etc.) to a KNOWN good running vehicle.

[zzlegend]

Good advice Kube.

[V12Bill]

If the heat riser is rusted shut, it will cause a sluggish engine. Voltage at the coil will vary between 3 and 6 v, depending whether the points are open or closed.

[malpais]

This test for leaks works good. You outta keep a fire extinguisher handy. One of those "don't ask me how I know" statements.

Gordon

[Charlie ny]

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Don,
Tough for an iron intake to 'rot' but not so tough for an aluminum intake.
I have some great looking aluminum wall hangers.
The give away if your alum or iron intake is leaking internally, usually thru
a heat passage, is pronounced detonation which cannot be eliminated thru distrib-
utor or carb 'massaging'.
Charlie ny

[Don]

Don't have any history on car,friend bought site unseen.but really look nice and price was ok and he's happy, that what matters,,Have swapped out carb and dist, coil and condenser,runs about same,need to CK see if manifold is aluminum ..Well get it he's about 85 yr old but does real good and still runs his full machine shop.He did unplug wiper hose and plugged vac source ,said it changed engine sound..??

[ford38v8]

Originally Posted by Kube

Don, I have NEVER seen an intake "go bad".... Little can "go bad".
.....

Mike, I guess you've never seen an aluminum manifold burn out the heat riser?

[TomO]

I would do a compression check and if the compression is OK, clean and gap the spark plugs and check the spark for a good 1/2" spark when the engine is up to normal temperatures. If these are OK, connect a vacuum gauge to the wiper port and try to adjust the idle.

I would also do a cylinder balance test, by shorting out 1 cylinder at a time and noting the change in idle. Any cylinder that does not change the idle is not working correctly.

With the quality of today's parts, changeling them out without a diagnosis, could give you additional problems.

There will be a small change in idle when the wiper port is plugged.

[Kube]

Originally Posted by ford38v8

Mike, I guess you've never seen an aluminum manifold burn out the heat riser?

I have but did not think this applied to this particular thread. 1941 had cast valve chamber covers as you know.

[Mart]

If I were to list the things that would cause an engine to run rough, I must admit a rotted out inlet manifold would be low on the list. To be honest, until I read this thread, it wouldn't have even been on the radar.

Mart

[Karl Wolf]

I bought a used intake, an old dual Navaro- from a popular and ethical supplier. Before installing it, I put just a dab of air into the heat riser side and found a dime size passage to the intake side.

I agree that it's very unlikely to have a cracked cast iron manifold but when you have the only one, you still have it.

Easy to check off the car by plugging one side and blowing a bit into the other side...

Karl