1800 Cold-Cranking Amps from (2) Optima 6-Volt Batteries (39 LaSalle)

[Scott Anderson CLC#26068]

A related thought, doesn't change anything previously written.

Towards Bob Schuman's comment regarding the (yes, absolutely go with the heavy duty switch not a light duty) electrical switch.

I don't know how much time you've had in this world of OCD (Old Car Disease) so apologies if it's redundant. Hoping that this might be helpful, while my car has a heavy duty switch, it's located in the engine compartment.Sorta seems logical enough, right above the battery (which in my car again is in the engine compartment not in the interior compartment like yours.) But if this is an opportunity for you to install such a switch, or if you have one also located there by the PO, I've found over time that the engine compartment location is less than ideal. It means that each time I switch the power off/on, I have to raise the hood. In my case, given my hinges are geriatric on a good day I'd really rather not burn what remaining material they have in them. Also, it would be nice to be inside the car where I could lock the doors and have one barrier to an unauthorized person switching it on to steal it.

HTH,
Scott

[Glen]

The grounding strap on the brush plate is only necessary if it is not properly grounded.  That seems to be common when the starter is restored and painted.  The plate is grounded by contact to the body of the starter and the body is grounded by contact to nose which is in turn grounded to the engine block.  If those contact points are painted then the only ground is the bolts that hold the starter together.  Those two bolts do not have the necessary cross section to allow full current flow when starting the engine hence the slow cranking. 
If the paint is cleaned off in all the contact areas the starter will run properly without the extra strap. 
Rust can also cause this problem

[Jay Friedman]

Glen,

Wouldn't you say that compared to grounding the end plate, there still is a bit of voltage loss when grounding through the body of the starter even in the best of circumstances in an old 6 volt system?  As Doug Houston mentioned in his 2007 posting, Oldsmobile in the late '30s saw fit to ground the end plate directly rather than rely on grounding through the starter body, so there must have been a good reason.

[Caddy Wizard]

Jay and I have been acutely aware of the need for proper grounding of starter to engine, engine to frame, battery to frame and engine, etc., in 6v applications.  For years now we have been very careful about ensuring that there is no paint between the various parts being grounded to one another.  And still, adding this auxiliary ground strap to the commutator end plate makes a huge difference.  Maybe it shouldn't.  But it does.  I theorize that the reason it does make such a difference is that since we are only working with 6v to start with and the electric motor in the starter needs a minimum of a certain voltage to energize it and turn over, even a small voltage drop due to internal losses at the various grounding interfaces in the starter itself can make a difference between good performance and poor performance.  Whatever the theory, Jay and I know that even when everything is perfect, adding the aux ground strap helps and does so in a noticeable manner.


Jay, I hope you don't mind that I am speaking for you as well...

[Jay Friedman]

Art, for once I'm (figuratively?) at a loss for words!  No, all kidding aside, I don't mind at all and agree totally with what you wrote.

[Glen]

The problem did not exist when the car was new.   Cadillac would not allow that to happen.  Sometimes people over restore their cars and create problems like this.    The current carrying capacity of a conductor is dependent on the cross section.  By that standard, the body of the starter has a cross section probably as large as the battery cable.   
My post was to make all aware of the cause of the problem so they could fix it.
It is your car and you can modify it if you want.   

[Caddy Wizard]

I've owned lots of 6v cars and I haven't "over-restored" them and created a cranking problem where none existed before I touched them.  Some cars are happy and some not.  I try to make them all work properly (and be "happy" cars).

Again, whatever the cause and for whatever the reason, this extra ground strap does help the performance of a 6v starter motor.

[dochawk]

Isn't brighter headlights, as opposed to starting, the usual reason for a 12v conversion?

[Caddy Wizard]

Some go 12v for lights, some for AC, some for modern radios, some for starting issues.  6v works very well.  But it won't power AC systems or most modern radios.  And many times folks get frustrated with old 6v cars in poor shape because they have the wrong battery or the wrong battery cables (skinny ones like used on 12v cars) or the engine is out of tune (and harder to start). So they take a shortcut and switch to 12v (although that creates other issues, usually).  I really like to keep 'em 6v and do the best I can to make the headlights and taillights as bright as we can manage with 6v (fresh wiring helps, as do good grounds, new bulbs, cleaned and polished lenses, etc).  For me, I get pretty good results and am quite happy with 6v.  I've only converted one to 12v (and that was for AC).

One little technology that you see in 6v cars that has sort of gone away is the use of a Fresnel lens in the taillights to focus the brake light/turn signal light directly backwards and allow it to appear quite bright for a good long distance as seen from behind.  So owners of the old ones should pay attention to the orientation of the lamp socket when doing a restoration of the light assembly, as it can put the wrong filament in line with the Fresnel lens portion of the taillight lens if you install the lamp socket upside down.  Very subtle, but important.  I wrote a tech article about this in the "49 Times" several years ago...here it is...http://www.1949cadillac.com/a-tail-light-tale/

[Caddy Wizard]

Here is a short video showing just how well a 6v car can start!  The video shows my 51 starting from stone cold and the car starts within a second or two.  This car is still 6v, with a rebuilt starter, an auxiliary ground strap on the starter, excellent cables, clean grounds, an Optima battery, and a PowerGen 6v alternator (to keep the battery topped up very well).  The engine is in great shape, the Carter 2bbl carb has been carefully restored, the choke works well, it has Pertronix 6v electronic ignition module, and the timing is right on the number at 5 degrees advance at idle. 

Really, it starts as easily as a brand new Chevy or Cadillac with fuel injection.

https://www.youtube.com/watch?v=ZSOc7BrHBr4&feature=youtu.be