The Stovebolt Site Forums The Shop Area The Electrical Bay Slow cranking on a 248

I know I have been posting alot but Im new to this age of truck and need alot of advice!

I have been working on a 1947 GMC 248 for a few months now and its just not cranking the way I think it should.
I understand that 6v systems dont crank very fast but Ive got my new truck hooked up to it and every time I engage the starter it only turns over maybe a turn, sometimes not even that much. Even with the new truck turned on and running about 14 volts it just doesnt turn over very well. I dont know much history on the truck but what does it sound like to you guys?
Poor Connection?
Weak starter?
Something major in the engine itself?

Thanks in advance

Check for proper ground.

Yes, I have considered that may be the issue, I just have the negative jumper cable clamped onto the frame. Should I ground it on the starter?

Make sure large enough cables, jumper cables frequently don't make enough contact to carry the load. Hook negative cable directly to starter bolt. Did the starter work before? Getting starter rebuilt is a good step in the right direction, dragging innards from worn nose bushing is hard to diagnose, worn brushes are easy to replace, overworking a worn starter is a good way to death.

Ed

Still a 6 volt starter? Be very careful jump starting with a 12 volt system. You should not leave the 12 volt battery hooked up for any extended time. With 12 volts the starter should spin fast. If it doesn’t you probably have a starter that needs a rebuild. Negative lead to engine block, pos to the pos battery terminal. If you have a 6 volt battery installed only use 12 volts for 15-20 seconds at a time or you may explode the 6 volt battery. Don’t ask me how I know. Wear eye protection.🛠

GMC......Positive ground?

Have you made sure the engine isn't fighting a rusty spot in one or more of the cylinders or some tight valves? NEVER, ever, assume anything when trying to resurrect a long-dead engine. If you haven't been soaking the cylinders in penetrating oil and you've made sure the engine turns freely by hand, stay away from the starter. Drop the inspection cover under the flywheel and use a short pry bar on the flywheel teeth to turn the engine by hand until any tight spots go away. This might take some time. While you're at it, remove the valve cover and soak the valve springs and stems liberally to avoid problems with sticky valves. Those GMC parts are scarce and ESSSSSPENSIVE- - - - -don't damage them by trying to force the engine to turn past a tight spot! My favorite rust buster is KROIL.

www.kanolabs.com

Jerry

Did 1947 GMC trucks have a positive ground system?

Rick

Yes they did, but the starter will crank the same speed on either polarity. The charging system and the ignition system will have problems if the polarity is reversed, however.
Jerry

When waking up an old engine, I always make sure that I can turn it by hand before I use the starter. Also sometimes I remove the plugs, squirt some oil in the cylinders and spin it over with the plugs out.

First: do as truckernix describes (and, also clean/set the removed plugs - and check/set ignition-points - and clean the rotor tip).

Then: might as well go back to step 1, and step 2, and step 3 (checking "electricals" first):

1. Check the condition of all battery and ground cables/straps
- good/clean cables/sheathing and ground-straps (no corrosion showing from within and covers/sheathing)
- correct gauge (00 to 2 gauge) for both the cable (battery to starter) & the ground straps (battery to frame, and frame to clutch-housing or starter bolt)

2. Check/clean/protect all battery-leads/feeds connection-points (coat with a copper-impregnated anti-corrosion grease)
- battery to starter connection for "hot" lead (negative for "power-lead" is preferable on a positive ground USA GMC)
- all ground-leads connection points (strapd/cables from battery to frame, and frame to clutch-housing or starter bolt)

3. Connect the battery leads (preferably for positive ground system)
- negative battery "hot" lead to the starter "power-in" fitting/connection-bolt
- positive ground battery ground-lead/straps
(battery to frame, and frame to clutch-housing or starter bolt; or, battery to starter bolt))

Crank using a good battery (6v preferred - 12v OK for short cranks)

If the engine cranks poorly/slowly, and the battery is good: the next suspect a probably a tight engine (or, an old/worn-out starter).

Other likely culprits:
- bad carburetor (with old/unclean gas)
- bad valve lash/gap settings

Thank you for all the insight, where is a good place to find a starter rebuild kit?

Anything beyond changing brushes and bushings and a general cleanup is probably best left to a rebuilding shop. Machining the commutator, undercutting the mica between the commutator bars, and changing field coils requires tools and equipment the average hobbyist probably doesn't have unless his name is Denny! If the commutator isn't badly worn, a quick shoeshine with medium-grit sandpaper is usually all that's needed.
Jerry

Where would I pick a set of brushes and bushings? Everything looked to be in pretty good shape when I cleaned it all up. No play in the main shaft or anything.

I'd start by checking with the local NAPA store, and ask for the oldest guy in the place, the one who still knows how to read a paper catalog. GM starter brushes and bushings were pretty universal from one car line to another- - - -at least up until the heavy duty commercial stuff got involved. Some of the online resto-ripoff places would probably be my second choice. 6 volt starters had a larger diameter armature shaft- - - -5/8" on the drive gear end VS 1/2" for 12 volt starters. I'm not sure if the rear bushing would be different size- - - -measure it with a dial caliper or a micrometer.

Even a little bushing wear can allow the armature to drag on the field coil pole shoes, so inspect the armature and pole shoes closely for drag marks.

Jerry

I'm with Hotrod on taking it to a starter repair shop. I enjoy fixing everything that I can, but those starter guys know their stuff and are not outrageous in pricing.Their goal is to be able to fix your starter for less than what a new one costs.The last thing I want to happen is to be dead in the water with a halfway DIY fixed starter.
Carl

Fortunately, there's a 2nd.-generation electrical shop owner close to me, a guy a few (but not many) years younger than I am. He's got a BIG store room full of core starters and generators he inherited from his father, plus new old stock parts from the 1940's and 50's. If he ever retires, I hope he's trained somebody younger to take over the business!
Jerry

Good advice all round, especially that about finding a starter/generator repair shop in
your area or sending it off and letting them do the rebuild. Simply cleaning up the
commutator and replacing the brushes may work for the short term, but a complete rebuild
will put things back to the way they were meant to work coming out of the factory.
I would say this about a 6v starter: There is absolutely no reason that it shouldn’t start your
Stovebolt engine if all is in proper working order. I.E., engine free and tuned, all
connections clean and tight, good battery and 6v starter in working order.

Because of some generous members here on the forum, I was able to get Old Blue back
on the road this summer. Also enough parts were salvaged to assemble a generator for
my ’54 and put a spare on the shelf for future mishaps.
Although these are pictures of a recent generator rebuild, much of the internals may require
the same attention for a complete rebuild, be it starter or generator.

A potted or wrapped coil can have damage to the insulation. Once the coil has been
checked for shorts or opens and determined good, it can be re-wrapped.
http://www.pbase.com/dennygraham/image/167974930
The lugs are often damaged and need to be replaced. This is almost always a must with
the starter contact lug, which gets burned from arcing. A soldering iron is not hot enough to
handle the job and a small micro-torch works best.
http://www.pbase.com/dennygraham/image/167974931
CAUTION: Care must be taken to keep from overheating the coil or solder joint when using
a flame. Here a heat sink is applied to the pigtail of the coil of this generator coil. A copper
starter contact lug requires a lot more heat and a much larger heat sink.
http://www.pbase.com/dennygraham/image/121814064

If you do decide to attempt a rebuild or wish to have your starter rebuilt, I would suggest
contacting Ken Warner at Classic Generator in Midlothian, TX. I’ve used his parts kits
for years and would highly recommend him.
http://www.classicgenerator.com/
Denny Graham
Sandwich, IL

Ginpole- is it not turning over enough so as that it won’t start?
My gmc is still 6v/positive ground and they do turn slowly, when compared to any 12v vehicle.

***If it turns over slowly and is right on the edge of starting or not starting, a good tip I learned is to press the starter button first and then once it’s rolling over turn on the ignition switch. That lets it turn without the back pressure of it trying to ignite until it’s rolling and ready.

I have never had cranking problems with 6v negative or positive ground, after following the advice I posted above.

Nonetheless, a good-condition starter is a pre-requisite.

Take care of all of the above - it will crank nicely for many years.

Right on Tim. But you just can't convince some people.
Denny Graham

Has there been any effort to determine if the engine itself turns freely? If not, we're arranging deck chairs on the Titanic for the best view of the iceberg! Even a freshly rebuilt starter in 100% condition isn't going to help until the engine is able to turn. Getting less than one turn of the crankshaft even with 12 volts applied doesn't sound too promising. Two pages of good advice isn't going to substitute for a couple of hours of hands-on work!
Jerry