The Stovebolt Site Forums The Shop Area Engine Shop Starter - '49 GMC

So I've got this '49 half tonne I bought last year, and I have yet to turn it over. I had previous starter troubles, and now I've gotten another. I've tested this starter on the bench, and when I have it on the bench, it'll turn and spin really nice when I jumper a battery to it.

This is the puzzler though; once I bolt it into the truck, it shorts. Doesn't even turn a little bit. I'm not using the truck wiring, this is just with a pair of jumper cables, one to the terminal, one to ground it. I've tried it so many times now. Shorts everytime.

Is there something I'm missing here? I appreciate your advice and insight as always.

Matt

Is the engine stuck? Can you turn it by hand? There could be bad bushings in the starter that lets the armature drag on the poles when under load. The drive may be engauging before the motor starts to turn.

What do you mean by "it shorts"? A "short" is a term meaning short circuit. In other words the electricity is getting to ground before it completes the circuit to where it should be going.

Sorry, a little more information that I forgot to mention:

The engine turns freely by hand, a full 360 degrees.

When I say it shorts, I mean the terminal crackles, or sparks, and sort of fizzles. Same behavior as when you simply short the battery.

Like I said, it doesn't really make sense to me. I'm quite experienced with circuits and wiring, so having it short like that is puzzling and extremely frustrating.

Is there anything I should be trying, something I may have missed? Thanks for the quick replies by the way.

Take the starter off the truck and bench test it.

Read for resistance from motor terminal on starter relay to motor frame. You should get 1 meg ohm or better. If very low - 1 0r 2 ohm I would check and ensure cable lug at motor is not touching motor

I'm a little confused. Do you have a battery in the vehicle? If so, it should be a 6 volt positive ground. Are you using jumper cables from another battery and possibly crossing polarity with the battery thats in the vehicle? If you have no battery in the vehicle, its pretty hard to get enough amperage through most jumper cables to crank a 6 volt. If you have light jumper cables, its quite likely that it will only sputter at the clamps. I use 4/0 cable with 500 amp welding clamps for a jumper cable on 6 volt.

tclederman - I have bench tested the starter per the service manual. I even have a growler and it tested fine on that too.

crenwelge - I have tried it with the battery in the vehicle, and with the battery on the floor with a pair of jumper cables. It is a good, 6 volt battery with a full charge. Yes, I did hook it up with a positive ground. You might be right about the amperage though. I'll try it again this evening, no jumper cables, battery in the truck. The battery cables in the truck, should they also be at least 4/0? I thought perhaps it was a bad ground, but settled on a short due to the sparking. I'll update with my results soon as a get in the garage.

Thanks!

Well, I kinda feel dumb now. It's one of those things you always read, and you just look at it, looks good, must be good.

Bad ground somewhere. I took off all the ground straps, and the battery cables, and got everything to nice bare metal. Terminals too. What do ya know, it turned over. Seems I've learned, once again, to always check the basics first.

On the bright side, I heard it turn over for the first time today! It sure did put a grin on my face!

4/0 is actually overkill, but it is what we have at the shop for our 18 wheelers. 2/0 is enough for 6 volts.