Common failure modes: W-series starter

Hi All!

One thing I noticed on this WD that I'm working on... is that it cranks really slow, takes lots of current to roll it over.  I've rolled it by hand many times, doesn't seem that hard.

I'm pretty sure there's something amiss in this starter.  It's stock 6v from what I can tell...  Are they series or shunt wound?

Are there any failure conditions or alignment situations that typically yield this result?

Actually, Don, I've got incredible current flow. I used 3/0 cable, direct bolted to the starter switch, the other bolted to a wire-brushed bolt on the block, and had it connected to an 8D battery with 6' of 3/0 welding cable...  hence why I asked about failure modes for the starter.  I thought that with 12v/1100A on tap, and a 5.8v drop on cranking was a pretty indicative of some other problem...

When the end bushings or bearings are worn, do they drag that bad (I wouldn't think so)... or, if it's series-wound, is it a quartet of brushes, where armature feed is on one pair, while field is on the other... or perhaps shunt, and I have a failed winding?

Is the WD starter, the same as a B starter?

Passing along some background info...

The drag problem can be very severe. Bad bearings will let the armature drag against the field coils. Field windings are mounted on the case and fed directly, not through the brushes. Armature windings are wired in parallel, and put the main current through the brushes. Starters also like to burn commutator contacts if stalled, particularly if over sized cables are used.

Bearings, brushes, bad internal wiring contacts, shorted coils are all problems. Worn commutator contacts let the mica separators poke up and lift the brushes. Older starters also suffer from solder joints gone bad at the connection between the commutator pads and the armature coils. This makes them turn slow for no apparent reason.

The main difference in starter models is nose piece, rotation, number of brushes and the type of bearings. Most of the cases of that time period are the same. There were really only a few basic models.

Dave, the advice above really separates slow cranking speed into two categories: current transmission to the starter motor and physicial problems inside the starter motor. If you have attended to all the current transmission needs, then the starter motor itself needs attention. Assuming that 3/0 cable is lighter than 1/0, I'd switch cables and make sure that you have a solid ground from the starter motor to the tractor - see if that cures the problem. Are you sure that you have a good starter motor switch? If all of these are taken care of, it's probably time for a rebuild on the motor. Do you have another similar motor that you know works well that could be switched into your WD? Good luck - starter problems can be really frustrating!

Gee Dave, I think your cable is big enough! Have you eliminated the starter switch from the mix? Odd as it sounds......it might be contributing to the problem, though the current drain you mention would say not. Sounds like it's time to get inside that starter!

Good morning, Doctor!

So how are those configured internally?  Is the earlier version carrying a bearing at the bendix end, and a bushing at the brushes?

I changer the starter bearings in my D-10 and it made a big difference, they are not that hard to change. The bendix end can be driven out and the other just run a tap it then screw a bolt in and pull it, or put a bushing on the bolt and turn the bolt pulling the bearing.

Here's what I did to solve the same problem you have: First I cleaned and lubricated all bearing surfaces, and when that only helped a little, I did what the experts recommended. That is, I cleaned out the spaces between the brush contacts on the rotor with a hack saw blade to remove the insulation and crude that builds a slight bump in the rotor where the brushes ride and often causes them to lose contact with the rotor and thus result in inefficiencies there. With good brushes and good springs to maintain this contact, the starter works like new. Over many years of use, the rotor surface pads will wear and the insulation between each pad does not, resulting in a contact problem.

Hmmm... great info, guys!  Looks like when I get home, I'll be dippin' the carb and yankin' the starter.  Think I'll pull off the tank at the same time (better starter clearance?) fill it with some bolts, and foam-rubber it into the tumber to clean the varnish and rust out.  Thanks!

well looks like most everything's been covered for ya, i rebuilt the delco starter on my WD and it is not a difficult job. a good cleaning, and new bushings and brushes and starter switch can do wonders...the delco starter for the WD has four brushes, four field coils, and is series wound as you described above, mine worked pretty good but it really pops off now, i would definitely use 0 ga. battery cables as a 6v starter draws twice the amps as a 12v starter

Well, I got it back... worked late at the office tonight, but took a few minutes to put it in.  It cranks better, but still not great...  My D17 cranks much better, as does my '48 B.  Turning it by hand isn't too hard... so I'm not sure why it's so 'cranky', but it certainly is.  I'll look into it more deeply tomorrow.