04/03/12

12V Model T Starter Conversion

As originally built the starter was made to deliver the proper torque from a 6V source.  Converting to 12V increases the torque as well as the no load RPM.  The first thing that I noted was a 6V starter operating at 12V really slammed into the ring gear.  However there are a lot of T drivers out there running 12V with no serious consequences.  Enter the culprit.... the snout bearing.  The babbit on mine was almost non-existent. This allows the starter shaft to flex away from the ring gear causing the gear mesh to be reduced. Take this to the extreme (mine) and the gears can jump and chip.  Now if the motor 'kicks back' because of too much advance plus the added torque of 12V.........the shaft bends and things go down hill from here.  My shaft was bent over 1/10" out of round. 

A quick trip to Chaffins Garage for parts ($45.00) where Dave straitened the shaft and I was ready to rebuild the starter and convert to 12V.  New starter gear (one piece), bendix parts, bolts and keepers and a used transmission bushing covered most of the new stuff.  Dave had found that there was a bushing with the proper I.D. to fit the Bendix shaft but required the starter snout to be bored out to fit.  I took the bushing to a friends machine shop and had the bushing press fit after the hole was bored. 

So far after three weeks it's working fine and sounds like a good running 6V starter on 6V.

The following article is from an Email by a friend who kindly shared his experiences with me.  So I include his comments here with his permission.

Instructions

I used 2 #10AWG stranded insulated wire to make connections.  This is equivalent to a #7 wire but easier to handle and to get.  It is pretty close to matching the copper bar normally used to "wire" up starters.  Take a good look at the field connections as they are for the 6 volt configuration.  The current comes into the terminal on top and splits, going to the left 2 coils and the right 2 coils.  At the bottom of each pair of coils, a soft wire cable goes to one of the 4 brushes.  These 2 brushes are opposite each other.  The other 2 brushes go to ground.

I cut the left coils, loose from the terminal, as can be seen in the picture.  I also cut the brush connection loose from the right set of coils.  Save this.

So now there are the right coils connected to the terminal, and the left coils connected to one brush.  Connect the bottom of the right set of coils, where the brush used to be, to the top of the left set of coils, where the terminal used to be, with 2 #10 insulated wires in parallel.  This is kind of tricky.  Strip the insulation from a few inches of a # 10 wire, peel off some of the strands and use them to wrap and tie the wires to the bar from the coil.  Saturate these connections with a rosin core solder.  A 150 watt or 200 watt soldering iron will be needed for this.  If you don't have one, borrow one or buy one.  Don't try to use a torch, the oil soaked frazzled insulation will not put up with a torch.  I then wrapped the connections with electrical tape as best I could, partly for cushioning and also to not have shorts.

Next, using 2 #10 wires, make a new cable for the other brush, which used to be on the right coils.  Put the lug from the saved cable onto this new cable and attach it to the bottom of the left coil at the same point as the other brush cable attaches to.  Make sure the lugs will reach the brush holders when the starter is reassembled.  The original brush cable was wrapped with electrical tape to control possible short circuits

What has been done, when you get this far, has been to change the field windings from a series/parallel connection to a full series connection.

The pictures show where fishpaper has been shoved between the windings and the frame and the pole pieces, to help the aging insulation.  It is important the coils do not short to the frame, and shoving this extra wiring into the coils could aggravate the antique insulation.
 

Conversion Schematic Diagram