why does the 45 turn over so hard?

It could be higher compression. If you were to check the compression that might give some better idea why it does this. Could be a weak starter, poor ground, or a bad or undersized cable or even a timing issue. Some say you know the timing is right if you have the engine at operating temp and run it to high idle, then back of all the way, it should backfire once or twice.

Just a thought, 

Edited by Jacob (WI,ND) - 29 Jan 2011 at 8:35pm

I would have to agree with ctucker and jacob on it being an electrical issue. Bad grounds will cause major issues with 6 volt systems. Another thing that happens with these old machines is the starter and ground cables get replaced with 12 volt cables. This is a no-no. The smaller cables won't let enough current get to the starter and will cause hard starting. If it was my machine I would clean all connections. Pull the starter out of its hole and clean the hole and the backside of the starter. Use electrical contact grease on all of these surfaces to ensure a good electrical path ,especially on that single jam nut/bolt that holds the starter in place.  Ron

After all these years if something was to tight I would think a problem would have developed other than hard starting. I assume this has been a working tractor since it was overhauled.

The hard to start hot sounds like my CA was before I found out about the battery cable size requirements of 6V vs 12V. 6V needs a minimum of 02 gauge with 00 being best. Cables for 12V are typically 04 to 06 gauge. To do the same work, a 6V system will require twice the amps as compared to a 12V system because you have half the volts. More amps need thicker cables.

Gerald, not according to Ohm's law. If the only change is volts, load staying the same, amps will drop.

I learned about ohm's law about 56 years ago. Hasn't changed yet. I learned about motors a little later. The starter is a series wound motor and its current when stalled (as when power is first applied) is limited temporarily by inductance of the windings and the wiring, but soon (in a couple millesconds) is limited only by resistance and with 12 volts applied that current will be twice what it was at 6 volts.

The torque applied to the DC motor shaft has several variables affecting it. There's the current, torque goes up proportional to current. More current, more torque. Torque goes up according to the number of turns in the armature that are in the magnetic field from the field poles. More turns, more torque for a given current. Then until the field poles saturate there's more torque from greater field current. Since in the series wound starter motor the field current and the armature current is the same, more terminal current means more torque. Current is reduced when the armature is spinning to generate a counter EMF called back EMF, voltage in the armature windings that opposes the flow of current in the armature to reduce the current. Which reduces the field current and the back EMF so the effect is less in the series motor than in the shunt motor.

The series motor has a useful characteristic of being nearly constant torque so the load determines the speed and a series motor with enough power (usually long about 2 or three real horsepower rating) with no load will reliably self destruct by turning so fast it throws the windings out of the armature slots. That constant torque is why small tools use a series winding for high speed, why starter motors have been series winding for most of their history, and why trolley and locomotive traction motors are series wound. These can all work with shunt wound except that the shunt wound (or permanent magnet field) motors tend to have a constant speed characteristic and if slowed by load they drop the back EMF and drastically increase the armature current. That would make the trolley climb a hill as fast as staying on level track, but would work at pulling the power plant to its knees.

The AC induction motor is considerably more complex and because its shaft speed is set primarily by the AC frequency, and the shaft load is usually set by the shaft speed, its power tends to remain constant with varying voltage and so low voltage makes it demand higher current. But its operating voltage for a constant frequency does not vary 2:1 except for very small motors.

Yes, doubling the voltage and holding the power constant takes half the current, but almost always that holding the power constant requires rewiring or rewinding the load device to change its resistance and that's true of an AC motor with reconnecting paralleled windings into series windings.

Both AC and DC motor operation is complicated by saturation of the magnetic core which tends to happen on shunt wound DC and all AC a few percent above the rated name plate voltage, depending on how conservative the design is.

Gerald J.

I don't wish to hijack this post but I have a question. My thomson B has a rebuilt motor with aluminum flat top pistons. They were all I could find at the time. It cranks real hard. The starter was rebuilt but it didn't help and it has a new 6v battery. I did find out that it will crank easier with the ignition switch off (distributer ignition). Why is this?  You can crank it over and hit the switch and it just about stops. It has new cables but maybe not big enough.

Amps = 1000 X kw/volts    Ac starter windings 2.4 kw  2.4x1000=2400/12volts=200                                                                                 (                    ) /6volts =400 not a very smart man just one who gets by scratching his head alot.   Thad ark. ignition load and timing advanced trying to light it off.

Another way to look at it can be compared to modern automotive electrical applications. Last time I checked, a fully loaded Suburban held the record with 28 modules all consuming 12V. When any programmable module has to be reflashed (programmed) it's key on engine off. 28 modules typically will run the battery down to the point of no start in about 10 minutes. That same Suburban has a 140 amp generator. If it were using 6V, the current use would easily double. Where we gonna put a 300 amp generator, and how much engine power is it gonna use?

Why is it when you whip out the correct formula  someones  feelings get hurt and they make a wise crack about knowledge?

A 300 amp 6 volt generator is going to take the same shaft horsepower as a 150 amp 12 volt generator or a 75 amp 24 volt generator. And fit in the same space if properly done. If I was to do a 300 amp 6 volt generator/alternator, I'd use the same wires as I did for the 24 volt, I'd just hook four wires in parallel in the 6 volt winding but use the same winding space with the same packing factor.

Gerald J.

Interesting I have never seen the service factor on a starter.  Insulation on a number 2 wire will handle 200 amps but not 400 amps.  welding lead is expensive!  Interesting thing about tractors centrifigual advance is they are all in at 800 rpms.

Edited by mlpankey - 30 Jan 2011 at 6:37pm

Pardon me I thought the question or post was on  a Allis Chalmers wd45 with a delco remmy 1111 series distributor . Maybe he should ask on the Johny popper forum.   A engine requires more spark advance at higher rpms or to be timed for the highest rpm.

Edited by mlpankey - 30 Jan 2011 at 8:54pm

I really dont see part throttle response being a issue on a tractor nor is it on round track and drag race engines which throttle seams to be operated the same ,at least when I am in the seat of either one of the three. I ran the advance locked out and total timming on the pulling tractor as I did when racing.