In one of the threads recently someone voiced concern that using 12 volts on a model T starter posed a damage hazard to the bendix or starter ring gear. Is this a valid concern? I had not heard this before. Does lower voltage (6 or 8 volts) make starter contact softer and lower the risk of damage? Any help with this will be appreciated.

Thanks,

Bill

The problem with using 12V is with the bendix engaging the ring gear. The bendix has been known to fail because of the way it slams into the ring gear when you use 12V. I purchased a 12V starter from Mr. Becker and I'm afraid it does the same thing as the regular T starter, but it sure works nice other than that.

We've never had a problem with our 're-wired for 12 volts' starters breaking bendix's.

Thanks guys. Now, what about the use of a resistor in the line to drop the voltage. Any thoughts on this?

Bill

William
If your are hell bent on using 12 volts on a stock Model T starter simply use modern 12 volt battery cables from the battery-switch-starter. This will reduce the voltage to the starter a bit and reduce the 60% torque increase.
Ron the Coilman

Many different resistors have been tried. Some folks use a Model T Bendix Spring to absorb voltage but the most successful is way is to run a long 12 volt cable rather than a short six volt one. I run my Speedster on a 12 volt battery at the far rear of the car and run a six foot 12 volt cable up to the starter. I know the voltage must drop under load but the initial snap at 12 volts is still there, Have not broken a Bendix spring yet and the car was built as 12 volts in the early 1980's

I have a 12V system on a stock starter however I have placed a bendix spring with large brass lugs in line. This seems to take some of the kick out of the hit on the flywheel. I read a lot about this not working but it does for me.

My interpreation of Ron's graph is that - if accurate - even with a regular T starter operating on 12 volts you only get a measly 20 ft - lbs of torque. A whopping 8 ft - lbs over what you get with 6 volts.

It isn't an issue.

The biggest 12 volt issue is the loss of cold cranking power by putting 6 cells in a 3 cell battery space and reducing the number of plates that provide the cranking current. Either the engine starts right away or you charge the battery again.

If it isn't an issue Royce, then why did you use some 10 feet of "12 volt" battery cable stored under your seat when you installed your 12 volt battery?

That was your car that I remember you telling us about, right?

If it's no issue, then why didn't you just stick with the stock stuff that Henry screwed together, throw the 12 volt battery in there, and just be done with it?

My only experience with a 12 volt battery was on the 26 roadster when I bought it. The starter used to slam against the flywheel ring. It would also lock up from time to time which I had to push the car backward in high to get it unlocked. The bendix had been broken before and brazed. After I pulled the engine and fixed the magneto, and replaced the starter ring and bendix. I put in a 6 volt battery. Have been using 6 volts without a problem for 20 years now. I have no idea how long it took for the 12 volt battery to cause the damage, but Was told by the former owner that he had to replace the starter. He only owned the car for a short time before I got it.
Norm

This needs to be read slowly!!.
When an inductor is first connected to the voltage,[in this case the starter is an inductor], the current rises after the voltage is applied. In a starter this rise is fairly rapid. Any resistance in series with the starter will not drop any voltage until some current flows. So the starter probably engages just as fast with a resister in series as without.

Once engaged the starter draws a lot of current and the starter is weaker than at 12 volts due to the voltage drop. However, the resistance gets warm or hot!

Summarized!
The Engagement is about the same on 12 volts with or without the resistance. The power to drive the starter is less with the resistance which, for high compression engines, isn't desireable.

As stated previously, many of us in Oklahoima City use 12 volts without problems. Just ensure the bolts holding the Bendix are seated well.

Any comments??

Regards,
Noel

PS: sometimes the weighted portion of the Bendix isn't seated tightly and will come loose. A small tack weld can stop this on 6 or 12 volts.

Noel,

I read it slowly, I promise.

IIRC, you missed out on the last discussion here on the forum. What I took away from it was this:

Yes, the starter behaves like an inductor but like you say, the current rise is very rapid - due to the fact that there isn't much inductance.

The starter is stalled (zero rpm) when the switch closes and that 12 lb-ft (at 6 volts) or 20 lb-ft (at 12 volts) is small compared to the inertia of the armature.

So, the combination of the above two statements ensures that there is considerable current before the starter drive engages the flywheel - meaning that added resistance will help somewhat.

I say "somewhat" because the resistance needs to be set for the correct starter voltage when cranking the engine and the current while cranking the engine is going to be considerably higher (but by no means three or four times) than the current from initial switch closure to drive engagement with the flywheel.

I wouldn't begin to argue with your success at 12 volts on a model T. I just wouldn't do it after all the flywheels I've seen that have come out of British cars with bendix-drive style starters.

Even the original Mini replaced its bendix-style starter with a pre-engaged one in 1985. Spinning starter drives must not be great for flywheel ring gears.

That's my take on it, for what it's worth.

Seth

We also go to a lot of trouble to reconfigure Model T starters so they work properly on cars using 12 volt batteries. I doubt that I would waste the time and money doing it if there was no reason to.

Damage to the bendix is caused by it slamming into the flywheel. Double the voltage on an unmodified starter and you have more slamming force. Damage to the flywheel is usually minimal unless you have the habit of starting the car while it's already running.

Noel
In a DC motor torque is proportional to the field current which is a function of the applied voltage. Yes, inductance is an initial factor, but by the time the starter armature is turning the effect of inductance is low and torque is high.
The torque curves in the diagram posted above were not calculated on paper, we measured them with two rebuilt starters, one with stock series/parallel windings field windings and another with the fields modified to fully series wound and ran the starters with a Prony brake and tachometer to measure torque and speed.
Ron the Coilman

The model T is a physical representation of the marriage of technology and economy of the times.

Its interesting how human nature urges us to try and better these cars all over again when its already been done as evidenced by the modern car. Its also interesting how many are drawn to these cars for their historic and somewhat primative technology but immediately work to change the properties of the vehicle that drew them in the first place.

Over my head for sure.

Vince M

Royce
In absolute terms an increase of 8 foot pounds torque is minimal.
But, in relative terms, the Model T starting motor was designed and specified to apply 12 foot pounds of torque to the ring gear via the Bendix drive gear. For the sake of argument assume a 20% design limit or maximum 14.5 foot pounds.
Running a stock Model T starter on 12 volts increases the motor torque 60% or 20 foot pounds, significantly more than any reasonable engineering design margin.
Somethings gotta give? And the elements at risk are the Bendix drive and ring gear, except apparently in Oklahoma where the laws of physics have been repealed and no one has this problem?. Grin, it is only a joke!
Ron the Coilman

Would you rather get hit with a 12 lb hammer or with a 20 lb hammer. That is how I see it.
Your ring gear and bendix should chime in here.
I have run 12v and sooner or later something has got to give.

I havefound that changeing 6v to 12v imostly done to overcome a electrical problem in the car If everything is up to snuff and the trans is left in high when parked the engine will start easily on 6v even in cool temps I have run my ford like this for over 20yrs and it always starts even after in storage all winter in Maine

I blew two bendix in a row soon after I installed a starter and 12 volts in a non starter car. Then I put a idiot switch on the timer rod so the starter would not engage unless the timeing was retarded. Have not blown a bendix in twelve years. I only know of one other broken Bendix with twelve volts and it broke for the same reason. Spark was not retarded.

"Its also interesting how many are drawn to these cars for their historic and somewhat primitive technology but immediately work to change the properties of the vehicle that drew them in the first place."
Well said, Vince M. That should be the quote of the year.

So has anyone pushed on their starter and gone for a ride today?

I have been using 12 volts for over 20 years, never a problem. I am beginning to think that starter damage is about elusive and inevitable as a broken crankshaft(which I have yet to experience) I think the fickle finger of fate is involved with both.

"So has anyone pushed on their starter and gone for a ride today?"

Yes, but my car is six volt, no plans to change it.

Thanks to all for the great input. Mine is a 16 with a starter added.

George, I'd like to see a photo or drawing of that 'idiot switch' that keeps the starter from engaging with the timer advanced. That sounds like an all around good idea.

Bill

I can't say much for 12V on a T. Mine is 6V. However, my wife has a '43 Farmall H tractor that someone had converted to 12V before we got it. Not long after we got it, I had to have the starter rebuilt. Coincidence? Maybe. It came back with a new bendix. After that, upon several occassions, the bedix would stick on it's "threads" where it spins out to meet the flywheel. The only fix was to pull the starter and physically "twist" it back with two pair of pliers until it popped back loose. Then, I noticed the rear plate (Back on the brush end) had a crack in it. It would still work so I did nothing. Finally, it quit. I found a starter in a junkyard and swapped plates. Fixed it for about a month, then IT broke. I was ready to convert it back. She let a guy talk her into "Modifying" the starter to take 12 volts. Don't know what he did. Solder a shunt in there or something? Anyway, it seems to be holding up, but we were putting a generator back on at the time (Alternator held the hood out about an inch and it could not be fastened on that corner), and a 6 volt generator and a 12 volt generator cost the same or close. I still wish she had gone with 6 volts, but it's her's and I let do with it what she will.

"So has anyone pushed on their starter and gone for a ride today?"

James, after installing a new 6v battery in one of my T's (and the largest cables I could get custom made for me at a battery shop) I could easily drive around with the key off until either the starter got red hot or the battery died - no need for 12 volts here !!! That's how I'd move the car around when there was no water in it and I had to move it.

Regards,
Garnet

"So has anyone pushed on their starter and gone for a ride today?"

Yes! I dug through the pile of crap in the garage and found my 23 touring car (I had a general idea where it was hiding!). It has not been run since I got home from the Centennial Celebration last July. I had done nothing to it except drained the water out of the radiator and disconnected the battery. I connected the battery, turned on the gas, stepped on the starter button and it fired right up (6 volts with magneto and coils). Pulled it out of the garage and cleaned all the junk out of the car. Went through and oiled and greased everything, filled the radiator, checked the oil and rear end levels and went for a ride. It ran great. Picked up the kids from day care which thrilled them. May take it out again tomorrow if I have time. Will definitely be taking it down to the Memorial Day parade on Monday, then over to a neighbors house to help him get his 13 speedster started. If I'm feeling ambitious I might even hose off some of the crud, or at least wash the windshield.

Dave S.

SETH,
Thanks for reading slowly. ;-]

The Bendix Gear and the Integral Inertial mass, when operating normally, is rendered almost inert for the first 1/2 revolution, [or what ever the Bendix takes to fully extend]. This means that a Bendix gear is supposed to extend and engage the ring gear with basically no rotation, not at starter RPM. Only when full engagement is complete is the gear yanked into operation and then the full torque [and current] is made available to the gears. This make the Bendix drive key and bolt very important.

As TIM stated, there is minimal damage due to this engagement process.

Then, RON,
Thanks Ron for the Technical Data. This is better than opinion any day.
I must agree with you Ron, that a magneto using 4 buzzers is a wonderful performer, [and one of Henrey's better developements for that era]. The faster we go, the hotter the spark. Just ensure that enough advance is available for high RPM ops due to the inherent coil lag.
As far as the laws of physics being repealed in OK, it is true. When the laws don't serve our needs, we just ignore 'em, ;-}
One old timer here has about 30 to 40 years on 12 volts with minimal problems.

Here, IMHO, is where we collectively stand on this issue.
If we choose to run 4 buzzers we need 12 volts for operation at higher RPMs. It has been well documented here in this forum that 6 volts is inadequate and the buzzers can't operate well in high RPM applications.

For distributers, it is optional.

For High performance engines, ie: Model A crank, high compression heads, etc, the choice of 12 volts may be either on option or perhaps, a requirement.

This has been a very enlightening and gentlemanly thread.

Regards to all,
Noel

I am using an A crank and a High compression head, so I OPTED for a 12 volt system.

BTW,
Has anyone determined the cranking RPM of a starter??

Noel

Noel
The original Ford specification is 150 RPM.
Ron the Coilman

Data according to Murray Fahnestock in his repair articles, the Ford starter has a free running speed of about 2400 rpms. Has torques somewhere between 14 and 16 ft/lbs. and draws between 175 and 225 amps. Draws about 100 amps free spinning and if the Bendix gets jammed can take up to 600 amps or whatever ever the battery can supply.

The Bendix has 10 teeth, the ring gear has 120 teeth, so the ratio for spinning the T motor is 12:1 for the starter motor.
The Bendix gear will disengage at approx 200 to 300 rpms as the motor starts or tries to start, that is the famous "rrrrreeeeeeinnng inng inng" sound when the Bendix disconnects and the motor is still not started....we all know that sound

For me, no 12-v battery needed or wanted in my Fords, just have a rebuilt starter, good fat cables and clean connections, and cleaned and good shape foot switch, and a proper Group A 6-volt battery in good condition, and you will be happy with the results.

Dan

Noel
We were originally talking about using 12 volts on a stock Model T starter and it's affect?
I would agree with you about using 12 volts for the coils if you have dysfunctional magneto (remember I wrote the original analysis of this problem), but that is not a SUMMING UP justification or analysis of the problems using 12 volts on the starter.
Must be something about petroleum migrating into the water supply affecting Oklahoma science? grin.
Ron the Coilman

Prolly!
Noel