Frustrating start problem

[rivcokid]

My 31 roadster is becoming more and more unreliable - so much so that I'm hesitant to take it out. Here's the issue: Sometimes it simply won't start on its own - by that I mean when I touch the starter rod, it sounds like the battery has been removed. Absolutely nothing happens. I can touch the rod 100 times and get the same result, but 2 days later, I can come back and it will start as usual. There seems to be no rhyme or reason to when it does this, except that I noticed it being much easier to start this morning with it being 95 degrees out. Anecdotally, it seems like the colder it is, the worse the problem.

When the car is in one of its "don't start" moods, I can start it with my jump pack with no problem - it starts right up with the 12-volt jump pack. I don't have to do anything to the car other than hook up the jump pack.

I've checked the battery both when the car will and will not start, and it is always good - 6.1 to 6.3 volts, and it will and won't start no matter where that number lies.
I've checked and rechecked the cables and connections, and there are no issues there. I have a secondary ground.
The starter spins very strongly - it was just rebuilt several months ago.
The generator indicates 7.2 volts.
I've removed and checked the starter switch and it looks fine.
There is a fuse on the starter and it is fine too.

In short, when the car works, it runs beautifully with no problems. When it won't start, it won't do anything until I hook up the jump pack - hence my hesitation to take it out now. There is no indication when it will change from wanting to start to not wanting to start.

Anyone have any other ideas? Thanks (again) in advance!

[Jim/GA]

Have the battery tested. Take it out, take it to an auto parts store and ask them to test it.

[rivcokid]

I have - it's fine. This is the second battery I've had also, since the first battery turned out to be bad for another reason. The problem happened with it too.

[Big hammer]

Dead spot in the starter motor? Starter motor brushes? You have stated the starter switch looks good, but thats where I would start ( no pun intended) after retesting the battery

[Marshall V. Daut]

Even though you write that you checked the battery cables, your problem is a classic poor ground description. It's a willy-nilly situation where for some unfathomable reason, the starter will turn over fine for days and then not respond at all unless allowed to sit for a while. Such intermittent go/no-go battery issues like this can often be traced to a poor ground where the positive strap is bolted to the frame. A secondary battery cable might not be able to overcome a poor ground here because it doesn't go directly to the positive battery terminal. The center crossmember directly beneath the ground strap must be shiny clean down to bare metal on both sides in order to provide a good, strong ground. Such a clean ground is more critical in a 6-volt system than a 12-volt. Remove the ground strap and sand/grind/scrape away all paint and rust from the crossmember, and then try again. I have had this same perplexing issue happen to me, too. I find that in our humid Iowa weather, I need to clean that grounding point every two years or the same thing happens to me that you're experiencing. I suppose smearing some dielectric grease on the bare metal would help reduce this rusting and oxidation beneath the ground strap.
I assume you have the correct 00 gauge 6-volt battery cables and not some auto parts store off-the-rack 12-volt cables?
Marshall

[Marshall V. Daut]

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By the way, the next time this happens, turn on the headlights. If they don't turn on or are very dim, you're back to a grounding issue. Check the ammeter needle to ensure it discharges when the lights are turned on. If the headlights do turn on and are bright, press the starter button. If the lights go out or immediately go super dim, there is still a grounding issue. The lights should only slightly dim when the starter rod is depressed, assuming the battery is good and charged up. Learn to use your ammeter as a troubleshooting aid. Henry put it in the spartan instrument panel for a reason!
Marshall

[Marshall V. Daut]

Here's another "By the way" comment to your initial posting. The fact that a 12-volt jump pack will easily turn the starter over is yet another indication that there is a grounding issue in your car. There is enough juice in that start pack to bridge a weak grounding point so that electricity flows the way it should. If the problem were a weak starter, bad switch or anything else, using a 12-volt start pack would most likely not help much, or if it did, the engine would turn over slowly. But you say that when using the jump pack, the engine starts right away. To me, that further re-inforces a poor ground.
Marshall

[David in San Antonio]

@RivcoKid - Sorry, I have no suggestions, but boy do I feel your pain. My Wretched Roadster had a baffling intermittent problem.
I think Hell might be a place where sinning souls are punished for all eternity, but just intermittently, with no apparent pattern. It's that intermittent factor that really causes suffering.

[Herb Concord Ca]

check the height of the copper button on the starter, forgot how high it should be, someone may know.

[stickshift]

I agree with Marshall 100% sounds like a grounding issue. When I got my truck, I had the same issue. It made a world of difference when I replaced both cables with heavy duty battery cables I ordered to fit from an Ebay store. They were twice the thickness as the ones at the auto-parts store. You can get them in any length and in either red or black. Even if you use an ohm meter and it's zero ohms, under a load you can lose amps which is what cranks the engine. In my case, the starter turns twice as fast with the heavy battery cables instead of struggling.. By the way, the fuse on the starter is only for accessories and ignition.

[400A]

I agree 100% with Marshall, but in the "for what it's worth" column I had the same issue a few years back. I cleaned all connections twice and made sure the ground was super clean. Changed the battery and starter. Same issue. In frustration and as a last resort I changed the battery cables. That solved the problem! Afterwards I slit the insulation off the negative cable and even though it looked fine on the outside, the copper was badly corroded under the insulation. You just never know ......

[rivcokid]

@ Marshall - Your explanations make the most sense I've heard! I did have grounding issues in the very beginning, and the fact that my jump pack works immediately every time further reinforces it. I'm going to get my wire brush out and give that cross bar a good once-over (both sides) and tighten that bolt down real well.

Thank you so much for your well-reasoned and patient explanation (I'm still new at this)!

Thanks to all the others too who confirmed what Marshall said!

[jerrytocci]

Your problem is intermittent. I suspect an electrical connection issue effected by the temp and/or humidity. Good luck

[Patrick L.]

You say the engine turns over fine when it doesn't start. check the voltage at the points when stationary and while cranking. It should be battery voltage and will flash while cranking. The primary cable is kinda famous for going bad and grounding where they screw into the distributor. If you don't voltage at the points [ when open] [ should be no voltage when closed] just keep working backwards to the coil and the terminal box to find the problem.



OK, never mind. For some reason I thought the engine spinning and not starting.

[Gene F]

Dead spot on starter. When it happens, have someone hold the button down with their foot, and you tap ont he starter case with a hammer. Or take the cable off, and put an ohm meter on it. Corrosion CAN happen under the insulation.

[rivcokid]

@Gene - thanks. Will try that too.

@Patrick - Thanks also. Will be playing with it this weekend if it's not too hot.

@Jerry - thanks. I'll need it!

[Marshall V. Daut]

To check if there is a dead spot in the starter, turn the ignition key off, put the transmission into third gear and get behind the car with your back against the rear of the body or spare tire. Then push against the car so that it budges forward a bit. Or get it to rock back and forth. It's easiest to do this in third gear. Budging the car forward will advance the crankshaft, flywheel and the starter's Bendix gear, moving the armature away from any dead spot. Then try to start the engine.
I'm not sure, though, how a dead spot in the starter would occasionally keep an engine from turning over, yet after waiting a while as the poster writes, the starter works again. I am suggesting the above test just to eliminate the starter as a possible cause of your intermittent trouble. I'm still betting on a weak ground as the culprit.
Marshall

[rotorwrench]

I would want to know if the armature in the starter was well tested during the rebuild. A person needs to growl them out and then test each segment of the commutator for shorts or opens. Dead spots in the armature are a real possibility as are dying spots in the battery conductors. If you use a cut off switch then that can be another source of trouble.

The bendix only engages if the starter spins so the best test is the growler and commutator test set. A person can pull the starter and test it in various locations but there are four brushes and no load on it so it may still rotate in that case.

[California Travieso]

[QUOTE=rivcokid;
Will be playing with it this weekend if it's not too hot.[/QUOTE]

Rivcokid,

Better get started early. It’s going to be 100 degrees Saturday. I went to Costco this morning for gas and to return some stuff I don’t need, and it was 95 degrees by 10:30 am!

David Serrano

[burner31]

Sounds like you've checked most things.
But have you looked at your junction box connections and behind you instrument panel at the connections there.
I had a similar issue...turned out to be a bad connection behind the instrument panel