Smoking ground cable

[WarEagle]

Finally got the rebuilt 300 back in and hooked everything up. Try to start it and the negative ground cable at the block starts smoking and the starter is slooow. Had the starter checked, its OK, battery OK, cables are 6 gauge (cleaned contacts, bolt and used dielectric grease). Block is also grounded to the steering column bracket. Getting spark at plugs so ignition system is good but it won't fire.
Could rebuild tolerances be that tight to slow the starter, or do y'all think its electrical? What else can I check?

Thanks

[WarEagle]

I just checked the voltage to the coil and it's only 6.43 volts.

[Mancar1]

Sounds like a bad connection. Make sure your ground cable is clean and has a good connection. Also check the block to body ground strap. It is also possible you have a bad battery.

[1972hiboy]

the coil voltage it correct if you have points. If all those things you say are checked good. I would double check you got the firing order right. It could be a tight new engine but that might be excessively tight if its really bogging the starter down that much. If the cable is smoking its moving alot of juice and getting hot so that starter is working insanley hard. double check all your connections but make sure your firing order is right. if the firing orer is right then try backing off the distributor timing a bit and see if that makes it easier to crank the engine over.

[WarEagle]

I am using points. I double checked all connections, cleaning them and using dielectric grease. Firing order is right (153624). I'm getting spark, but it doesn't fire up. Moving the dizzy doesn't seem to help it turn over better. Would a thicker gauge cable help? Both to starter and to ground? Both are 6awg.

[1972hiboy]

are they the same cables you had before?

[WarEagle]

Yes Same starter too. All worked fine before the rebuild. The machine shop sold me the block, crank, rods, pistons, rings and bearings. Of course, the crank turned easier before the pistons were installed. It was harder to turn after all was bolted up but I just figured cause it was new. The pistons were marked .030" and they said the block was bored to match. If it wasn't, do y'all think that small a difference (.030" piston in a stock cylinder) cause enough friction to slow down the starter?

[1972hiboy]

.030 differnece in all cylinders I would think lock the engine up entirely

Can you rotate the motor with a breaker bar and socket? just for fun have you tried hooking up a charger to the battery for a bit then tried to start it?

[sargentrs]

Block is also grounded to the steering column bracket.

You might want to move that ground strap. Mine have always been from the block straight to the firewall. You can see it in this pic (forget the red circle). It's the place to the right of the red circle above the pedal bracket nuts. You can see where the white paint was under the strap.

[WarEagle]

.030 differnece in all cylinders I would think lock the engine up entirely

Can you rotate the motor with a breaker bar and socket? just for fun have you tried hooking up a charger to the battery for a bit then tried to start it?

I can turn the motor with a breaker bar, but it is tough. I have charged the battery and even tried to start it with the battery charger at 80 amps (jump start mode). It doesn't help.


I did have the ground strap at that same spot you show, but felt the metal was too thin, plus the bolt started getting loose from over tightening. Is the bracket not good?

Thanks for all the diagnostic help !!

[tbone6]

Is your battery negative connected directly to the engine block as well? If not, start there. 6 ga. might be a little light but not by that much. Go grab a ground strap (not a cable) from Oreilly or Auto Zone, and eliminate any doubt.

[WarEagle]

Is your battery negative connected directly to the engine block as well? If not, start there. 6 ga. might be a little light but not by that much. Go grab a ground strap (not a cable) from Oreilly or Auto Zone, and eliminate any doubt.

Yes, negative cable goes right to block. Thinking about adding one from the block to frame also. I'll get a strap for both.

[fmartin_gila1]

Way in the past when I was working as a fleet mechanic on these particular pickups & trucks, ensuring a good ground path eliminated a lot of weird problems that would crop up now and then. I always went directly from the neg term on bat to the block first, then block to frame, then block to cab, and frame to box or whatever was on the back. Number 6 is marginal for a new or tight engine, 4 would be better. You might try to crank it with a set of jumper cables as an extra load path until it loosens up a bit. Just leave the wiring you now have installed in place and jump from the bat + to the solenoid and bat - to a good clean bolt head on the starter.

Fred

[WarEagle]

Way in the past when I was working as a fleet mechanic on these particular pickups & trucks, ensuring a good ground path eliminated a lot of weird problems that would crop up now and then. I always went directly from the neg term on bat to the block first, then block to frame, then block to cab, and frame to box or whatever was on the back. Number 6 is marginal for a new or tight engine, 4 would be better. You might try to crank it with a set of jumper cables as an extra load path until it loosens up a bit. Just leave the wiring you now have installed in place and jump from the bat + to the solenoid and bat - to a good clean bolt head on the starter.

Fred

That seemed to help a little bit. I was thinking how to get some of the load off the starter and realized I could take out the spark plugs to relieve the compression. The motor is cranking longer, 5-6 seconds before the battery weakens, so I'm going in the right direction. That's even with the charger on the 80 amp starter setting.

Another question then arises....How soon could the motor turn easier? I would think a couple hundred miles? That's a lot of cranking time!

Also, the battery is rated at 850 cca but tested at 683cca and 12.71 volts. Battery Source said its still OK but would replace it for $31. (kinda contradictory, huh?) Should 683 be enough for this situation or should I trade it for a fresh one?

Thanks

[1972hiboy]

you load test a battery by loading it by half its cca reading for 10-15 seconds. it shouldnt drop past 10 volts. so you should have loaded it to 425 and held and checked the voltage reading. id say you battery is fine. in fact it seems like maybe your readings are to good. loading that battery to over 600 amp and it didnt drop the voltage at all? something is going on.