But if it only is an issue when it's hot, by the time he has it out to bench test, it would seem it may have cooled enough to turn. Would a shop that can test it be able to actually check any factors that would be sub par even when cool and that would indicate likely failure when hot? I'd still look to just jump across the solenoid to see if it cranks when hot.

 

Good point - Screwdriver test is MUCH easier on a F-body where the terminals are easy to get to from the top due to the log manifolds. Ram horn manifolds make that a challenge. Headers might allow you to get to them depending on the pipe layout.

Extra wires added and hooked up in advance for a diagnosis is smarter here. You do not need anything huge, just some small wires about the same guage as the purple "S" terminal wire. One connected to the battery lug on the starter and the other connected to the tiny "S" terminal. Leave everything else in place. When the car is hot and not starting, you can make sure it is out of gear then short the 2 wires together (Use a remote starter switch if you have one). If it does not crank, the starter has a bad solenoid at a minimum.

 

I agree with POST#22. You can set up a remote starter while the engine is cold so when it does not work you have another way to 'bench test' it. But the possible flaw in this is that the wires you are going to use have also been heated up just like the wires that may be heated up so much they can not work.

I have driven cars with issues like this up on my wood ramps so I can slide under car and get the starter off in relatively quick time and bench test it while it is still hot. Yes...this isn't one of the most pleasant jobs I have had to do. But sometimes it is needed to be done. Working around and with parts that are HOT.

I also see validity in the timing be way too advanced causing it to not want to crank up when hot. I guess I read into the first post that the starter was not even wanting to engage and try to crank the engine.

DUB

 

[QUOTE=DUB;1597481720.... I guess I read into the first post that the starter was not even wanting to engage and try to crank the engine.

DUB[/QUOTE]

thats how i read it......no cranking at all. OP is that true?

 

As an alternative, a set of jumpers. One lead on the S terminal and the other on the bat lug on the starter (e.g. red on the S, black on the lug) Then to crank just touch the other ends together. BUT note, the free jumper clamp on the lead off the Solenoid S will be hot - touch it to any metal on the car and it could short. Touch it to the other jumper clamp and the starter will certainly crank when cold and may crank when hot if the solenoid is the issue. If going this route, I would keep the free clamp on the hot side covered with something non-conductive except when you intend to touch the two clamps together to see if the starter cranks.

Also note these may need to be real jumpers, i.e. with heavy cables, not skinny booster cables. Since you're looping up one cable and down the other they'll add a lot of cable length between the bat and starter so they need to be low resistance. The cheaper booster cables may have too much resistance when looped like this and cause too much voltage drop to allow the starter to crank even when cold.

 

Electrically hot and temperature hot wire absolutely, .....thick wire? not required. It either cranks or it does not crank. The temp of those added jumper wires is insignificant. There is not a lot of current draw for the solenoid so GM used a skinny (hot temperature exposed ) purple wire for it from the factory. You can too. The exercise is to see if the problem is excessive resistance in the starter control circuit OR a problem in the starter itself. If you crank with the jumpers, you have excessive resistance in the control circuit. If no crank, the problem is in the starter.

 

I'm no expert, but you may have more than one issue that you are dealing with that is causing the starting problem.
I'm collecting parts for my 496 and probably over researching each part and componant that is going into the build.
1. My research told me to stay away from the mini starters as they don't do well with heat soak and that nothing works better than a good OEM type starter with a heat shield.
2. I had a battery ground cable that looked to be in good condition, but was heavily corroded under the insulation and was not conducting well. It may help to conduct continuity and resistance checks on your ground cables.

 

The set up proposed though is to bypass the solenoid contacts which route the battery directly to the starter. Maybe I used the improper terminal reference to the solenoid. I assumed that from an earlier post noting the S terminal that that was the terminal with a lead directly from the battery. If not, then which ever post on the solenoid comes directly from the battery is what the jumper needs to be attached to - or just go to the battery if they are long enough (my set is).

The current draw then through the jumper to the starter is significant. I have seen on multiple occasions people trying to jump start a car with booster cables and not get it to crank. But when I hand them my set of true jumper cables the car will crank without a problem. Likewise, I've seen situations without a crank on a single set of cheaper cables be able to get a crank when two sets of cable are doubled up. I learned this when playing with cars in my grandfathers garage when we couldn't get the flathead in a 32 Ford Roadster cranking over. It was a 6 volt system which draw twice the current 12 volt systems do for the same power. So trying to boost it with charger set to boost on 6 volts required heavier cables. And I saw it again in the oil field trying to start small diesel generators off our car batteries. This is a case where size may matter.

It is not an issue of heat. It's and issue of wire resistance due to the combination of higher resistivity (a cable half the diameter has 4 times the resistivity) and length (a set of jumpers may be 10' long and this setup will run out one and back through the other - so 20' maybe). Couple that with hundreds of amps used to crank a starter and the voltage drop in the cables can become factor. Making a short hop from the solenoid isn't a big deal as it's just a few inches. So a small cable can manage it for a short time, though it's going to get hot really quickly. It's also the reason why a steel screwdriver of moderate size can work even though the resistivity of steel sucks compared to copper.

Lastly, note that I said in the post the test "may" need good cables. My concern was that this could be tried and result in no cranking and lead to decision that it's a bad starter when it was actually the solenoid failing due to heat. If this is tried and it doesn't crank, I'd recommend trying it again with heavier cables or a double set (though that would become awkward) before scrapping the starter.

 

Nice post. Supports the issue of ministarter concerns which, though we use them in small planes, we are very disciplined in how we use them. 10 seconds cranking at most then rest for minute. We're dealing with carbs in small planes and on these older vettes. They don't start on the first spark plug that fires and so put a lot more stress on the starters. Your comment about corrosion inside the cables hits on the issue cable resistivity issue. Corrosion breaks down the ability for current flow to use all the strands as it's difficult for the current to freely move between strands. Add to this an elevated temperature, 100 F increase in the wire will raise the resistance over 20%, and you can again get an excessive voltage drop on the cable.

 

You are confusing the control circuit with the cranking circuit. The control circuit is only a small electrical signal in the purple wire from the key. If there is a lot of resistance in the control circuit (neutral safety switch, bulkhead connections, old patched up wiring, corrosion), the solenoid will not have enough juice to pull the plunger in. The solenoid does 2 things - it pulls the starter gear in to mesh with the flywheel AND once it finishes that, it sends the big power to the starter motor from the fat red battery cable attached to the solenoid. The starter motor itself will not even begin to try to turn the engine over until after the plunger in the solenoid pulls all the way in. The starter motor is not powered at all until the plunger is pulled in by the control circuit. That's when the starter cranking motor gets energized from the big red battery cable. A large amount of amp draw will occur only after the key signal is successful first. Not enough juice in the control circuit, no solenoid movement, no big power draw and no cranking.

 

I am not doubting your research....but your observation is the first post i have ever read with anyone say anything bad about ministarters..... mostly with headers the full size starters even with heat shields just don't stand a chance with the collector being right next to the starter. my experience with hi torque mini starters has always been good and always solved the problem.

now i suppose if i had a failing mini starter and replaced it with a full size starter and heat shield i would be singing about the glory of full size starters and heat shields

 

Here's a really EASY test:

Connect a jumper cable from the starter frame (or a bared portion of the front starter mount, if it is still installed) to the negative terminal on your battery. Then try to start the engine. If it starts (when it would not immediately prior), then the ground circuit for the starter is KAPUT! Whether it is a 'rotten' wire inside the insulation, a bad solder/crimp joint at a terminal, or poor contact between a ground wire terminal and mating surface doesn't matter. Success with that test is telling you that if you find the fault[s] with the starter ground circuit, the problem will be fixed.

So, is running a jumper from battery negative to the body of the starter too much to ask?

 

All I know is that when I turn the key, I hear a loud click, but nothing turns

 

What I did with the remote starter is that I hooked up the bat wire when cold, and also installed a 3" jump wire with the purple wire.After heating everything up, I put the second cable of the remote on the jump wire, and still got the same result, click click click, No rotation

 

As a lawyer once said to me during a deposition, I'm asking this question with a smile on my face and joy in my heart , have things changed from 40 years ago when my mud soaked brother started the his suburban with a screw driver to jump from the solenoid's battery cable to the starter battery input? My understanding back then was that it was the spin up of the starter that drove it to move the shaft forward so its drive gear could engage the flywheel. Was that incorrect? Likewise on small aircraft engines today (which haven't really changed since the 1940's) I know that if it cranks and doesn't start that the starter will stay engaged with the flywheel behind the prop. It doesn't pull back because of a control circuit. It won't disengage until the the engine actually starts. But I haven't dealt directly with starters in a long time, so if they have changed it's good to know. Likewise, if I've been wrong in my understanding for 40 years, well that's good to know too. Thanks,

 

vince vette 2....

You weren't wrong 40 years ago, either.

 

Not quite - The starter motor does not rotate at all until well after the bendix gear is meshed into the flywheel ring gear. The bendix rides on a shaft that has a helix ground into it so the bendix rotates as it slides forward as it meshes with the ring gear. If the key is released and power is taken away from the control circuit, the solenoid spring will retract the bendix gear from the ring gear.

Open up a starter. There is a plunger piston inside the solenoid. The electrical magnetic field in the outer part of the solenoid causes the plunger to move forward like a piston in a bore. The plunger is connected to a lever so that when the plunger moves, the lever pivots on a fork which slides the bendix gear into the flywheel. Once the plunger reaches the end of its stroke and the gears are meshed, the last part of the stroke strikes a button in the end of the solenoid that makes an electrical contact which sends power to the big windings in the electrical motor. The electrical motor then turns, and the engine cranks.

The solenoid was a marginal design from the beginning. It just barely works even when everything is cool. GM had design issues many years ago and the fix was a softer solenoid spring to help the solenoid plunger pull in under hot conditions. The resistance caused by heat affects the performance of the electrical windings. Lots of heat and you get the click, but no movement of the plunger piston.

Age, corrosion, taped connections, neutral safety switch, ignition switch, harness bulkhead connections etc also affects the conductivity of the wiring so the plunger does not have enough juice to pull in. Heat stresses the solenoid and the old wiring resistance on an old car adds to the problem.

The screwdriver across the terminals works because it bypasses all the electrical resistance in the harness. Full battery power from the big battery lug to the tiny "S" terminal allows the strongest magnetic field possible in the solenoid. That allows the solenoid to do its job and pull in the plunger piston in, and all the rest works after that.

Bottom line - Adding a relay only helps if the screwdriver across the terminals helps the engine crank. The relay just takes the place of the screwdriver.

 

Well this is fun, at least I'm learning something. Thanks for explanation. It encouraged me to dig up the circuit, which I’ve added to this post.



Note - screwdriver not original equipment

The first thing I note then is the goal would not be to jump from the S post to the starter via the M post. That would simply give a low resistance alternative path to running through the two windings which have relatively high resistance due to the typical small wire sizes and long windings used on solenoid activation coils. It may well just allow the current a path straight to the starter motor and not actual the drive mechanism (I’ll use the GM circuit schematic terms). Further, as that circuit is hot only with the ignition in start, there would be no voltage at that point unless the key was held in start.

Instead, the jump required is from the B (battery) post to the M post. I’ve conveniently added in a screwdriver to the circuit to show this. Note that not only will this provide power to the starter motor, but it will also energize both the pull in and hold in windings by feeding into the pull in winding at the M post and then out to ground by joining to the hold in winding at the S post. The only difference at this point is that the pull in winding won’t de-energize because there is no 12+ V on the starter switch side to oppose the 12+ V now coming from the M post.

So getting back to the OP’s issue, at this point I see a couple possible scenarios once the screwdriver, jumper cables, remote switch or whatever links the B and M posts.

1 – The starter motor does nothing. Then it’s the motor that has failed when hot because once there is 12 V to the windings it should spin unless there is some switch not shown in this diagram which prevents it from spinning if the drive mechanism is not engaged.

2- The starter spins but doesn’t crank the engine. Then there is something wrong with the pull in and/or hold in windings that shows up when they are hot. This could include a bad hold in ground since, I assume, it takes the power of both windings to move the drive mechanism.

3 – The starter cranks the engine. Then the windings and the starter are working, so the issue would have to be upstream and heat related.

This is all based on looking at just this one schematic. So, if there’s more to it or I just misinterpreted what's there, always a distinct possibility, then I’m open to further education.

 

Screwdriver needs to short between "S" and "B" as I am describing it. "M" has no voltage at rest so it will not help anything. You want to pick up full battery power 12V from "B" terminal and send it to "S" terminal.

 

If the problem is that the solenoid is not closing the motor contacts, which are designed to transfer hundreds of amps to the starter motor, then the only way the starter will crank is because those hundreds of amps are transferring through the pull in winding which I doubt it was gauged to handle. Alternatively, it could avoid that by having a relatively high resistance. But that means it will restrict the current enough that the the starter won't crank due to the voltage drop across the pull in coil winding.

I apologize, but I don't see the point of that jump. Jump the battery straight to the starter and it will either spin if it's good on not if it's bad or, I'll add, if its ground is bad, in which case neither the pull in winding or the starter will kick.