Starter Issues...

[Bill VA]

Have a thread going on the MF section, but posting here to get a wider audience....

Recently replaced the solenoid on the starter for my formally trusty MF50 diesel as the thought was it was welded closed. With the new solenoid in place, turn the switch, nothing. Battery is good and fully charged.

Today, I bypassed the key starter switch with a momentary push button switch. From leg 'L' off the voltage regulator to the 'S' terminal on the solenoid. Keep in mind the solenoid is new and starter is almost new. The idea was to rule out the key switch and neutral start switch as the problem and see if the solenoid and starter would work as advertised.

Push the switch (range and gears in neutral and the fuel shutoff - off), the starter spins like a champ - yippie!!!!!

Let off the switch, the starter keeps turning - dang. Luckily the hot side of the battery wasn't cranked down and I quickly pulled off the cable to the starter.

Put the battery cable back on, no cranking (as it should be), pushed the momentary switch, starter spins great, won't stop spinning - again quickly pulled the battery cable to the starter.

Almost new starter, new solenoid. What the heck is going?

Again what got this going was a low battery and the thought that I had welded the solenoid via low voltage. Changed out the solenoid, turned the key and nothing. Today's effort was to bypass the switch and be sure the solenoid/starter would work, isolating the switch, but what I've got is a continuous running starter motor after initiating a start via the switch.

What do you think is wrong?

Thanks!
Bill

 

[Ragnarok]

I do know that low voltage can stick a solenoid...that or maybe the Bendix or fork hanging-up?

Did you remove the starter and strip it down and lube it?

 

[Steve@Advance]

Think there is probably 2 problems here.

The first, no start with the key switch, is either voltage drop to the solenoid, or a problem with the starter switch or neutral switch. Try the starter switch again witha volt meter on the S terminal. If you get a low voltage, like down around 9 volts or less, there is a voltage drop. You can add a relay down at the starter to overcome the drop. If no voltage, check back toward the switch, bad switch or neutral switch or bad connection.

As for the starter locking in and continuing to crank, that is a mechanical problem in the starter. The spiral on the shaft that the drive runs on, it pushes the drive to the end of the nose cone when cranking. The drive is going too far forward (missing thrust washer) or the shift fork is in backward, something causing the plunger to push too deep in the solenoid, holding the button it, holding the contacts in the solenoid closed.

Once the engine starts, it will kick out. But something is wrong inside the starter for it to do that.

 

[Janicholson]

The starter can stay cranking (without starting the engine) only if it keeps getting electricity. The only place it can get electricity is from the solenoid. The solenoid is either staying "ON" because it is jamming, or because it is still getting electricity in its coil. If you jump from the hot terminal on the solenoid to the S terminal with a screw driver, and it still stays cranking, it is a mechanical issue. But because it stops doing it when tha battery is disconnected, tltctrical sems more likely. Jim

 

[old-9]

First thing I would do is take the cable off the starter , hook up a light to the cable or solenoid so I could see what was going on. This way you are not turning the engine over. Then ,if it still showed the solenoid was energized, you can trouble shoot to see why. I would also make sure the solenoid was the correct one. joe ex electrician

 

[caterpillar guy]

Did you get the rubber flap that is there around the solenoid slug folded over or otherwise? If your working with a smaller wire it might just weld things up from not enough amperage carrying capacity or the solenoid is staying on.

 

[Andy Martin]

Or your push button is sticking.

 

[Case Collector]

If your schematic of the solenoid is correct once the solenoid is energized the contacts will close
and send voltage thru the 2nd coil and keep the contacts closed

 

[kevinthefixer]

(quoted from post at 18:49:04 08/27/17) If your schematic of the solenoid is correct once the solenoid is energized the contacts will close
and send voltage thru the 2nd coil and keep the contacts closed

I think if you look real close it shows both solenoid coils going hot from the keyswitch via the neutral safety, one coil grounds directly and the other grounds through the starter motor windings. IDK why they'd design it like that. I agree it's not the best diagram in the world. But it should still shut down when de-energized.

 

[kevinthefixer]

It does show the two coils in opposite polarity, presumably if the motor starts and over-revs the starter, or even if the keyswitch is released, the second coil should disengage the starter as the power feeds back into the first coil.

 

[used red MN]

I agree with Steve about the starter being held engaged by the starter drive coming out of position on the thrust spiral. But in order for this to happen the solenoid has to be the type that electro-magnetically assists the starter drive to engage in the flywheel. That mechanical connection works in reverse and keeps the solenoid contacted when the drive travels to far. So when you replaced the solenoid did a plunger fit into it or did it mechanically attach to an arm on the starter? If so what I found several times in Delco starters in the automotive field is that the snap ring that retains the drive on the armature shaft comes out of place. The snap ring once in the groove has an outside retainer that slips over it sometimes these break. I know you say that the starter is almost new but with mechanical things anything can break when least expected. So you need to pull the starter and verify all is in tach there. Now if the solenoid is not integral(attached) to the starter and has no mechanical connection all this jabber means nothing in your case.

 

[Steve@Advance]

Kevin, that's the way Delco starters have been forever. The solenoid has 2 sets of windings.

The first winding is grounded through the starter post. (That's why a Delco starter won't even click when the brushes are worn out.) That winding is the most powerful, as it has to overcome the plunger spring. Once the solenoid contacts connect, that coil drops out of circuit, the second takes over.

The second winding is just strong enough to hold the plunger in once seated. It is grounded internally to the case.

There are 2 reasons for this design. One is to avoid needlessly consuming battery amperage. No need to keep the more powerful coil energized once the plunger is seated. The spiral shaft drive keeps it mechanically engaged.

The second reason is to prevent the solenoid from overheating during long cranking sessions.

 

[Bob]

"It does show the two coils in opposite polarity, presumably if the motor starts and over-revs the starter, or even if the keyswitch is released, the second coil should disengage the starter as the power feeds back into the first coil."

Kevin, Kevin, Kevin! As a "fixer" this shouldn't have been the first time you've seen a starter solenoid with two coils, a "pull-in coil" and a "hold coil"! Typical starter solenoids are made like that.

You are reading WAY too much drama into this... the "pull-in coil" is in series with the starter and draws a lot of current /provides a lot of magnetism to initially pull the solenoid closed, then is switched out of the circuit once the solenoid contacts close. The "hold" solenoid winding remains energized as long as you are cranking the engine, and is able to hold the contacts close with a lower current draw than was needed to close them in the first place.

 

[Bill VA]

Both windings are powered by the battery? No chance the residual power from the generator is powering them? If battery only, then once the key is removed from the start position, the solenoid has to disengage. If that is true, then I've got some mechanical failure going on with the bendix? If the bendix, given the starter is nearly new and spins, can it be replaced?

 

[Bill VA]

Relay to remove the solenoid power from going through the switch and directly from the battery through the closed relay contacts. Control voltage for the relay can be low as it is simply opening a set of contacts?

 

[Steve@Advance]

Bill, the problem isn't the starter drive (Bendix) itself (unless it's the wrong drive, too long).

What happens is the shift fork, (that initially pulls in the drive), that is attached to the plunger, when the drive is spiraled out to the end of the shaft, the torque of the starter then holds the drive against the thrust washer at the end of the starter housing. That in turn holds the plunger seated in the solenoid TOO DEEP, which holds the button in the end of the solenoid (which makes the contacts that spin the starter) IN when it should have a little slack, just enough to release the contacts when power is removed from the excitation coil.

It's a little hard to understand at first, but if you take the starter apart and study each component, it will make sense. Somehow there is wrong geometry between the plunger, shift fork, and drive travel. It's not a real common problem, but can be a mind bender when it happens. Typically it is the thrust washer is missing behind the snap ring that holds the drive on the shaft, the wrong starter drive, or the shift fork is bent or has an offset and is in backward. If you can't find a solution, take the starter to a starter/alternator/generator shop. They have seen this before and will be able to spot the problem.

 

[Traditional Farmer]

I had a brand now solenoid on a Ford pickup (1989 model) do that with a brand now solenoid good battery etc.Went and got an old all metal tractor solenoid put it on the truck and its worked perfect ever since.I'd be looking at the solenoid even though its new the contacts can still stick.

 

[Janicholson]

Great answer. Well stated. Another example of real insight. Jim

 

[Pappy]

I had a similar problem last week. Put a new solenoid on my '88 Ford
F150 and it worked well for two days, then the next time the starter
motor would not turn off. Got the solenoid replaced by the dealer and
all is well again.