Here's another carburetor mystery, Folks.

[T. Cotten]

Here's another carburetor mystery, Folks.

Schebler and Linkert models that use a lowspeed needle lift lever have a spring collar that meters air.

The seat for this collar varies from perfectly machined, allowing the collar to slide slightly with the arc of travel of the lever, to what appears to be horribly eroded.

Here is a very late model that shows it, as well as a much earlier Schebler DLX, attached.
(Attachments are in reversed order, naturally.)

History's mystery is: Were these actually produced so horribly as casting flaws?
Or is it some sort of wear?

It is hard to imagine enough airflow beneath the collar to erode that much potmetal or bronze without it ending up somewhere.

Serious thought please,
Thanks in advance,

....Cotten

[sirhrmechanic]

Could it be some kind of electrolytic corrosion/oxidation? Unlike metals, moisture, time? Bronze is usually pretty immune from oxidation. But... time can do funny things. And it will pit/erode.

Interesting pictures and question. Look forward to the discussion on this one.

Cheers,

Sirhr

[Robert Luland]

That's what happened when they took Luigi off the saw line and moved him up to casting finishing.

[T. Cotten]

That's what happened when they took Luigi off the saw line and moved him up to casting finishing.

Brilliant Bob.

We knew we could count on you to waste bandwidth.

SrHr!

Although I have encountered a pre-War steel collar or a couple of Linkerts, virtually all Schebler and other Linkert collars were brass (plated of course), so upon a bronze body, a dielectric erosion seems unlikely, and it occurs nowhere else.

More pics attached; The two Bonne seats demonstrate how the irregularity follows a pattern.
The last shows how no machine marks remain, although a great many carbs of both marques remain cleanly machined.

We may never know.

....Cotten

[Robert Luland]

How about the fact that the steel disk vibrates all over the thing along with road grit. No problem. The deeper groves are easy. The owner installed the disk up side down and the rest is history. the waste of band with was you asking the question. Bob L

[T. Cotten]

More photos, Folks,...

First attachment shows a Schebler with a "dished" seat, yet retained its nickel, suggesting it was cast that way.
Second is an example of extreme concavity upon a Linkert.
Third is an example of what appears to be real collar wear that does not resemble the others at all.

Please remember folks, that the collar is under stiff spring pressure.
If the erosion is to be blamed upon grit drawn beneath the collar by airflow, one must ask why it is not observed at the venturi vents, where much more volume is drawn.

If cast that way, confounding both the collar's sliding action and its air metering accuracy, why were they not machined like most?

....Cotten
PS: Note also that the collar can only be mistakenly inverted on models with the larger bore.

[Shaky Jake]

You come up with the most interesting puzzles, Cotton. You seem to be the expert on these things, so it's probably unlikely that someone else will come up with the definitive answer. When I look at the pictures, it occurs to me that there may be more than one type of degradation going on here. Some types of wear are caused by use, some are caused by the lack of use, and some are caused by people with good intentions.

Kevin

[pisten-bully]

Any chance that each carb was individually tuned on the bench after casting? A quick and dirty calibration done with varying degrees of finish?

[T. Cotten]

Here is what little I know, Folks,...

The Armored School Handbook is the only contemporary information I have available, and it describes function:

"Air bleed is effected in this (low speed) circuit from two sources. One inlet for air is down beside the low speed needle, which is held in place in its guide by a spring and a spring seat washer. This permits air to vent down beside the needle and to begin mixing air with gasoline as the fuel is drawn past the seat of the low speed needle."

We are led to believe that the hole in the collar (spring washer) is a metering orifice.
If the collar does not slide, it will wear upon the needle. If air bleeds under the collar, then metering is defeated.

Note that most seats for the collar are nice and flat, as shown by the M344 in the first attachment. A dished seat prevents it from sliding through the arc of travel of the lever.

Let us consider how these must have been manufactured. With sandcast models, we must presume the well was drilled, and the counterbore for the collar in the same setup.
It is hard to imagine this part of the casting would be left unfinished, and just as hard to imagine that there was some sort of airflow beneath the collar to erode it like a blasting nozzle, without wear at the needle or collar hole.

The dishing is definitely not a machine operation. And its irregularity follows a pattern, with the deepest "wear" often in the same place, as the partially reconditioned seat in the second attachment shows, also an M344.
( I have photos of good and bad M74Bs also, made much later. One would think that if it was a manufacturing defect, it would have been corrected.)

This has baffled me for some time.

....Cotten

[exeric]

What do the corresponding collars look like?

[T. Cotten]

Eric!

99.8% percent of collars show no unusual wear upon their bottom surfaces at all, inspite of the seat "erosion".

Indeed, after finishing the tops as faux "cad" or "nickel", I only need to scrub them upon newspaper with my index finger to bring the bottoms to a shine, and slippery enough to slide as they should,.. given that the counterbore seat is dressed, of course.

(If they have been run through a plater, however, it is a bit more complicated.)

One would think that if there was an airflow of abrasive gunk involved, it would be mirrored upon the bottom of the collar.
But it is not.

....Cotten