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Would like to install 12v solenoid type starter from 235 in place of older 6v stomp starter. Are the ring gear & starter teeth compatible? Say a 1957 chevy car starter mounted in place of the 6v foot activated starter in a 50 model truck? Wiring should not be a problem, just wondering about the gear teeth meshing. Thanks1

Short answer, no. 12v and 6v starters and ring gears are different. Different gear angles on starters, different number of teeth on ring gears.

Not only do the ring gears have a different number of teeth but the flywheel diameter where the gear mounts is different so you can't swap ring gears on the same flywheel. You'll have to come up with a 12 Volt flywheel.

What you might be able to do is mount the 12 Volt solenoid on a 6V starter and run the starter on 12V. Running 12 volts through 6V starters is commonly done. Mine has lasted 25 years and 100,000 miles like that. You might have to come up with a solenoid-mount starter or drill holes in the starter to mount the solenoid. I don't think the stomp-starter switch holes will line up with the solenoid holes.

I think it may depend on the truck capacity. I believe on 1/2 ton trucks it's possible to swap the ring gear on the flywheel. At least I've seen that posted here before. The 12V ring gear is 168 teeth versus 139 teeth on a 6 volt.

What’s the easiest way to count the ring gear teeth with the engine is still installed?

Take the flywheel cover off and start counting. Mark your starting point with white out or grease pencil or something and turn the engine by hand.

12v key start solenoid will not work on a foot activated 6v starter. The nose cone is cast for the accommodation of the solenoid activated bendix. One cannot swap nosecones because the 6v and 12v armature shafts are different diameter.
Soooo.... you will need a 168 tooth 12v flywheel/ring gear to go with a 12v key start.

6V passenger car starters had a solenoid engagement from about 1951 on. Also cabover and step van trucks. You might need to install a 12V solenoid to avoid burning out the solenoid pull-in winding pretty quickly. There's a 12V solenoid for a mid-1950s Olds or Buick starter that can be adapted to the Chevy 6V solenoid starter.
Jerry

This is a "12 volt" (168 tooth) flywheel. A "6 volt" (139 tooth) flywheel has a lesser number of teeth in the same dimension. You should be able to take this measurement without turning the engine.

I also scribed and painted white marks at 120 degrees and 240 degrees for TDC of cylinder pairs 2&5 and 3&4.

If someone would take a picture of a 139 (6 volt) tooth flywheel with a micrometer spanning 10 points on the gear like my picture above we could turn it into a quickie tech tip. Questions about flywheel teeth come up often here on Stovebolt.

i just happen to have a 139 tooth flywheel sitting in the garage.

[on edit]Bill, I just noticed that your pic shows the caliper spanning 9 teeth. We'd need apples to apples here.
[on another edit] I see that you started at 1, where I started at 0 in my count. I'll go take another pic to repost. Standby.
[editing again] OK all fixed now. number of teeth match in both photos.

I have a 54 chevy Bel Air in my "collection". It has the 6V key operated starter with the solenoid mounted on the starter field case. So, if I get a 12V solenoid this might work? Any idea on the possible part number? I would be okay with leaving the rest of the starter at 6V for now.

It might also be possible to wire a heavy resistor in series with the solenoid winding to prevent damage to the pull-in winding. Here is a selection of ceramic resistors on Ebay. I'd recommend the 10 ohm 200watt.

www.ebay.com/itm/225854220831?

Jerry

I took my original 6V solenoid to the local starter /generator/ alternator repair shop and they matched it up to a very close fit that has worked well so far. The advice I was given was that even though a 6V starter will live on 12V very well, the 6V solenoid on 12V will hammer a the ring gear teeth too hard.

So what you are saying is that by lowering the voltage on the small solenoid terminal with the resistor, when using 12v, it will prevent the hammering of the bendix into the teeth and provide"normal " operating voltage of the pull in winding? I would think that the contact points in the rest of the solenoid would be okay with 12v going to the starter.

My truck was born a 3 speed on the column. It has passed down in the family and my dad had converted it to 12V. It always had a 6V starter on it and other than turning over faster, it never gave a problem. It started easy going faster. Then I found a hydra-matic frame and driveline. I switched it all over but kept my engine. The H-M uses a solenoid starter. Knowing that finding a new flex-plate/flywheel for H-M would be a chore, I took the starter as mentioned to the local specialist. They gave the advice that while the starter motor would be fine with the 12V, the solenoid would work but they felt it could hit the teeth too hard so they matched the original solenoid as best they could with a new 12V version they had on the shelf. It never occurred to me to ask what its original application was for, in case it ever needed to be replaced. I just figured I would match it up again if that day ever came. This looks to be a very similar part. https://oldchevytrucks.com/el2171.html

The solenoid that bolts onto the housing instead of being integral with the nose cone was used in the mid-1950s on Buick and Cadillac, and probably Oldsmobile engines. Those marques went to a 12V system a year or two before Chevy in 1955. Yes, the "pull-in" winding of the 12V solenoid is what the concern is about. 12 volts is carried by the big contacts directly to the armature and field coils of the starter. Once the starter is turning, the heavy current pull in winding is disabled by having the same voltage on both ends of the magnetic coil, and a much lower current "hold-in" winding keeps the drive gear engaged in the flywheel.

Standard Motor Products SS 201 at Rock Auto:
1954 Cadillac

www.rockauto.com/en/moreinfo.php?pk=42691&cc=1320837&pt=4188&jsn=944

Jerry

That 10 ohm resistor would limit the solenoid coil to a max of around 1.3 amps Jerry. I don't think it would operate on that low amount of power.

The resistor in my link has a sliding tap on it. The same ad has a 5 Ohm 200 Watt resistor available that would also work. I'd move the tap to a position where the solenoid would work efficiently without excessively stressing the drive unit. There would be no need to use the entire capacity of the resistor. I chose that one for its heavy construction and ability to dissipate heat. Of course, it would only be in use for a few seconds, but I'm a believer in overkill whenever possible. It's also MUCH less expensive than a 12V solenoid.
Jerry

All good info- If this is attempted the lever between the solenoid and starter drive would be needed and also the metal "cylinder" that fits into the 12v solenoid would be needed-it pulls the lever when the solenoid is activated

No- - - -just obtain a 6V solenoid type starter, and either install a solenoid with a 12V coil, or use a low resistance, high current resistor to control the current flow in the solenoid pull-in winding. The resistor is a simpler, MUCH less expensive option. The solid steel plunger on the 6V starter should also work on the 12V solenoid if you choose to go that route. It IS NOT possible to convert a foot pedal operated starter to solenoid operation.
Jerry

I have thought about doing this from time to time but never carried the thought experiment all the way through like it seems we have here.

So starting from scratch,

1) I obtain a 6V key switch starter for Chevrolet complete with solenoid and linkage.
2) Then I order a B,O,C 53 or later solenoid and bolt that to the Chev field case. (Olds did use such a starter 53 and after, I had one.)
3) I now have a 6V starter armature and field windings, engaged by a 12V solenoid, all running on 12V.
4) 12V fed from the key switch to the solenoid should engage the starter pinion as though it was all 12V Chevrolet from at 55.2 or later Chev.
5) The starter will run at 12V speed as, in my case, it has for 20 years.

So for the price of a Key-switch starter plus $80 to Rock Auto I get a functioning Key-switch starter on my 12V conversion (originally 6V, still 139teth) flywheel.

Am I missing anything?

Sounds like you've got it covered. I think I'd try the resistor in the pull-in winding circuit first- - - -it might save you the cost of buying a 12V solenoid. The only time the heavy current is an issue will be the fraction of a second when the pull in winding is engaging the starter drive. Once the gear is engaged and the armature is turning, the heavy winding is disabled, (same voltage on both ends of the pull-in coil) and a MUCH lower current winding keeps the gear in mesh. That's a really good engineering feature that was built into GM solenoids.
Jerry

The good GM engineering has tripped up many troubleshooters. They don't realize how MUCH current the pull-in windings draw and it's only for about 25 miliseconds. So if the battery terminals are dirty as in spring and fall, the solenoid won't pull in before the battery terminals "pop." The starter voltage essentially goes to 0V and then immediately returns to normal. The lights work before and after you hit the starter, so people would blame the solenoid and not bother to check the battery terminals. Lack Of Maintenance rules again.

When I worked at Fluke in the eighties, I wrote an application note of various electrical tips and techniques: one used the 20 millisecond, peak-hold function on the multimeter along with a dc amp-clamp that would capture the current peak on the starter pull-in. It turned out that pull-in peak current was higher than the total starter draw during cranking. Something like 90A IIRC. Fords were considerably higher as I recall and had problems because of undersized wiring even if the battery terminals were clean.

We gave out those application notes by the thousands, often a case at a time, to the point where paper cost became a budget item my boss was mad about. He didn't care about how may multimeters we sold (lots). Snap-On had a standing order on every print run. I think the only one I have left is a color press-proof (the printers had trouble getting the yellow right).

A good multimeter and a knowledge of ohm's law and you can diagnose a lot of things with one hand in your pocket. Jerry might have run across that Fluke App Note in his shop classes. They would have showed up about '86 or so. I still feel like I did a good turn for all those techs who were otherwise flying blind with meters that didn't even come close the the truth. Along about 1990 we developed an automotive-specific meter, the model 88. I still have one. My dc amp-clamp died though and I miss it.

Do you still have that Fluke App Note? If you could take a pic of it and post it, that would be great. I'd like to see it.

[On edit] Fluke has a bunch of those application notes on their website, but I couldn't find that specific one. Here is one on using a digital multimeter for DC voltage that may cover what you're saying about capturing the highest or lowest voltage. I think you could get the same results measuring voltage as amperage.

"If it works- - - - -it's a Fluke!" I remember that one from way back in the dark ages!
LOL!

Ford used a pivoted field coil pole shoe to engage the gear into the flywheel instead of using a dedicated solenoid like GM. Even a little rust on the pivot pin dramatically increased the current draw to engage the starter pinion. Not much of a problem down here in the sunny south, but it was definitely troublesome up in the great frozen north with all the salt on the roads for six months at a time!
Jerry

Ah! I see. looking at the website I see Fluke has reverted to feature-oriented application notes rather than task-oriented notes. That is one of the great communications battles I fought and thought I had won for good. This is the constant battle between sales and marketing communications.

You don't come at a problem wondering which feature will make sales happy; You come at a problem looking for a procedure that will lead to the solution. The notes I wrote were all task/procedure oriented i.e. "Here's a procedure you can use to find a cause, and here's what to do about it when you find it."

But with complex systems there is a limit to that approach and maybe Fluke has come up against that. These are the two factors that novices and many experienced techs fail to grasp: you're viewing the effect, now go find the cause. You may need a meter to view the effect in enough detail to lead you to the cause. With enough experience you can dispense with some of the cause/effect process and play the odds game but understand that's what you're doing -- playing the odds. Like knowing about Ford's pole shoe problem for example.

The odds game was more effective in the old days when there was a finite number of failure modes, as in cars before computer systems. But now there are potentially more failure modes than incidences of a particular failure, so the odds game doesn't work so well. And now, sometimes you run the scan tool and come up with several codes so the task becomes finding one or more causes that have the error codes in common. Here again you're playing the odds game but at least you have a fighting chance and can check some voltages that might not show up in the scan tool data stream. Experience matters.

One very useful test we used to do when diagnosing slow/no crank symptoms was a "series resistance test"- - - -done with a low reading voltmeter, not an ohmmeter. Using the 0-2 volt scale on a Sun analog voltmeter, we would check individual voltage drop across every conductor and connection in the cranking circuit, hot and ground. Dropping more than 0.1 volt across any connection while cranking on a 6V starting circuit indicated a dirty or loose connection, and any voltage drop at all from end to end of a battery cable or ground strap was reason for concern. 12V systems had a wider tolerance- - -0.2V drop per connection, and 0.1V for conductors. I used, and taught that procedure for over 30 years.
Jerry