MTFCA Forum

I recently purchased this coil tester, and I thought others may want to see it and offer up any additional thoughts or details. I have more questions than answers, so I think I’ll just start with a list of some observations.

• Similar to an 18-Z-245, the 17-Z-429 part numbers are cast onto the various castings with an added letter suffix for each different part. I’ve never seen a 17-Z-803 in person, but I think they are the same way.
• The spark ring has degree lines but no numbers.
• The commutator shaft is gear-driven off of the main shaft. Both shafts are fully supported by bearings, so the unit spins very smoothly and easily by hand.
• It has ¾” thick magnets, single-stack oval coils, and no starter notch.
• It has a bronze, non-script commutator roller.
• The two gears have helical teeth, and neither is a Model T part.
• The magneto gap is readily adjustable at the lower front of the unit.
• There is also a thumbscrew that threads into the frame and pushes against the back of the field coil. It is easy to flex the field coil with this screw. It wouldn’t prevent the field coil from being pulled toward the magnets, but it would perhaps take the flutter out of it or bring a larger bottom magneto gap down to what the gap at the top is.
• The flywheel is not from a Model T, but rather it has its own 17-Z-429 part number.
• There is no pulley or handle on the backside, unlike the 17-Z-803, but the rear shaft lock ring does have two tapped holes where something else could be mounted. The ring set screw is actually set into a woodruff key slot, indicating the ring quite possibly isn’t the original arrangement.
• The Weston 156 ammeter serial number is 22366, but the meter mounting arrangement isn’t original.

Now for some assumptions:
• I assume the unit originally had an ammeter and a voltmeter and that the magneto gap could be adjusted to set the voltage for a given rpm.
• The magnets, field coil, commutator roller, and meter may not be original to the unit. This isn’t to say that they are or aren’t but to say that we don’t know and they are changeable things. The meter paper has the same language (magneto and coil testing instructions) as on the 18-Z-245, but this tester doesn’t appear to have a means of testing a car magneto. There is no inductor. The original wiring is long gone.
• The crank handle, commutator case, meter mount, and coil box likely aren’t original to the unit. This is to say that they could be, but based on construction it’s unlikely. The current crank handle location likely just had a nut with the unit being rear driven.
• I am guessing the unit was driven from the rear, either with a crank handle or motor pulley/gear (or a handle/motor combination of both). The shaft out the rear has a woodruff key slot, a small cross hole, and a shoulder. I’d be interested to know how the handle/motor combination on the 17-Z-803 attaches.


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I found one other unit similar to this one. It is in Smithsonian storage (not on display). If anyone has an inside contact that could get more information on this unit, I’d be most interested. This is not an operational unit (no gauge), and it appears to have been prettied up for display (a lot of plating and a modern-looking placard). However, I’ll point out that it has single-stack coils, a starter notch, and degree numbers on the spark ring. You can make out what appears to be 17-Z-429 near the screws on the spark ring, but the number isn’t fully legible in the photo so it is possible that it is not a 429. The rear shaft support casting is a different shape (different casting) than on the one I have. The Smithsonian unit has an additional base that appears to be well made and fits the unit very well. There is a motor directly coupled to the tester. I’m interested in people’s thoughts on this motor. Did they have VFDs capable of slowing the unit down to around 60 rpm back then? Would they have run this unit at 1700+ rpms to simulate engine speeds? Is it a slow DC motor? Other possibilities? The base, motor, and coupler aren’t necessarily original, but they definitely look the part. The way the coupler attaches to the rear shaft doesn’t seem to be the same as the location of the woodruff key and small cross pin hole on mine. The spark needle on the Smithsonian unit appears to thread in and has a hex just above the threads, whereas the needle on this unit and all of the 17-Z-803 units I’ve seen have a smooth needle simply clamped.

Smithsonian Tester Images
https://americanhistory.si.edu/collecti ... ah_1692890

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There is a similar unit shown here at the Trafford Park Assembly Plant in England, circa 1914 (perhaps late 1914 based on firewall/dashboard styles). It seems to potentially have a large motor behind it. Note the two gauges; the one on the right appears to be the voltmeter, as you can see the glint off of the adjustable marker knob on the face (assuming it is a Weston 156 Voltmeter or similar). I suspect they were testing full coil boxes and potentially the commutator and loom at the same time prior to firewall/dashboard assembly in the background. Note that the footprint against the lighter colored benchtop appears to be more like this tester’s rather than that of the one in the Smithsonian.

Trafford Park Assembly Plant, circa 1914
http://www.motorgraphs.com/heritage/for ... 54452.aspx
Higher Resolution (and mislabeled)
https://www.gettyimages.co.uk/detail/ne ... popup=true

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This Highland Park Plant photo published in April 1914 also shows similar units. Note the rear arrangement appears to be different than the one in the Trafford Park images (smaller motor or pulley set going down into the bench?) These units also appear to have two gauges each, and you can make out the magneto gap adjustment mechanism below the spark ring. Like the Trafford Park tester, there also appears to be commutators in the same place as the 17-Z-429, but the photo isn’t clear in this area.

Highland Park Plant Testers, likely 1914
Page 132 (page 144 of the PDF scan), April 1914 Edition of Automobile Trade Journal
https://babel.hathitrust.org/cgi/pt?id= ... 14&seq=144

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The earlier coil testers shown at Highland Park Plant circa 1911/12 (Kingston T-4238 coils in background) have the field coil in the rear and the flywheel to the front, degree numbers on the (very different) spark rings, no commutators built in, grease cups on the shafts, and shields over the spinning flywheels.

Highland Park Plant Testers, circa 1911/12
https://www.thehenryford.org/collection ... =gs-416718

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Perhaps someone on the forum knows some additional background on this particular tester. I got it just outside Detroit, MI in Canada. Prior to me, it was purchased a few years ago from a Model T enthusiast’s widow in the same area.

Does anyone know of any other 17-Z-429 testing units? The more information the better, as they all offer up their own little details.

I’d also love to see any other factory photos (or higher resolution of the same) that show coil testing stations. It would be great to get them in the background of another shot at an angle that shows the backsides.

Nik
Thanks for posting the photos of your coil tester find. That is new one on me?
We are all familar with the coil testers developed by Ford and introduced to Ford dealers in 1919 for maintasing ignition coils. Tis unit is described in the HCCT Manual Page 7
Over the years I have seen five different variatios of earlier coil testing aparatus. But they all have one basic function and that was to operate a trembler coil with a spark gap to view the spark output.
Every time a see a different variant the distinction I see is that it must have been designed to perform the same function for a different reason.
After the commonly known 18-Z 245 HCCT and its clones; another variant is the factory coil test apparatus depicted on page 6 of the HCCT Handbook. There is no doubt that its purpose was to test the thousaounds of coils for correct oprtation to supply the Highland Park Model T production line.
The other earliy coil tester variants, with the exception of one, all seem to be desinged to used by Ford dealers and servation stations to maintain Midel T's already in operation. Obviously, these were made by Ford and but their dates of availability and breadth distribution is unclear.
Until the advent the 18-Z-245 HCCT this need had been well known to Ford owners and dealers.
The 17-Z-429 variant shown in your post is very unique. It has some very unique features not normally rrelated to field servicing igntion coils ; the timer, the apparant (Smithsonian unit) ability to vary the coil tester speed, the ability to vary magnet (rotor) to field winding (stator) gap, the ability deal with the commonly known and somewhat problematic lower half of the field ring vibration in early Model T's. All this leads me to believe the coil tester shown in your recent post was most likely a Ford factory or engineering laboratory tool used for research on the ignition system design.
Perhaps all these earlier coil testers were solutions to specific problems to solve the problem of coil service and are just precursors to the simple and elegant design of the commonly known 18-Z-245 HCCT Ford introduced to Ford dealers in 1919?
Another Model T mystery?

This is another version that can be hand cranked or belt driven

Don
The coil tester in your photo is a Ford part number 18-Z-803 described in detail on page 19 of the MTFCA HCCT Handbook.
Ron Pattersn

Thanks, Ron and Don! I'll post photos of the four 17-Z-803 testers that I have saved off of the forum. I have questions for Ron on one of them.

Of course, there's Don's posted above. I'll call it #1.

Then #2... Then #3...

Then #4...Ron, these two photos came from you. Do you have a photo of the back of it? It seems like the starter notch may be on the lower right, and I can't make out an output terminal at the top of the ring. This indicates to me that the field coil may mount upside down like many other later testers. I could be all wrong, though. There's only so much one can get from pictures.

Most coil testers have the fiedl ring monted with the solder ile on the bottom. That makes the wireing routing easier. .
I have seen some of the early units with the magneto terminal solder pile on the top.
Either way, it makes no electrical difference.
Ron Patterson

Ron, three of the 17-Z-803 testers above have the output on top, but #4 appears like it might have it on bottom (based on what looks to be a starter notch at bottom right and that I can't see an output block at the top). If true, this would also mean the rear casting that the field coil mounts to is different than on the other three. I'm curious as to whether or not I'm seeing the photos correctly or not, as that would be a fairly substantial design difference between units (but agreed, not electrically). Do you know who has this unit (#4) now? Some additional photos would be most welcome.

Also, separately, you once mentioned that you saw a 17-Z-803 at Greenfield Village. I was recently there and didn't see it unfortunately. 1) They move stuff in and out of storage, and 2) there is so much to see that it is easy to miss something. Do you have photos of that tester, or do you remember what building it was in (I might go back)?

Thanks!