Inliners International Forums General Discussion Electrical GMC 6V verses 12V Identification

I have a GMC 6 cylinder engine from the 1950's? The engine is complete with starter, generator, and ignition. How can one tell if the engine came from a 6 volt or 12 volt truck? Thanks

One way is to check the Delco Remy tags on the gen and starter for part numbers and then cross ref them at a friendly parts store. Often times the tag also said 12 Volt right on it and that would be even easier for you. All else fails run the starter off a 12 v battery and jumper cables. If it spins pretty quick it is 12 volts. If it spins like it wants to go into low orbit it is probably 6 volts.

If you can read any of the printing on the coil they usually say 6 volt or 12 volt, or "use with external resistor" which is a 12 volt coil.

Any idea what this engine might have come out of?

The 6V starters ground (1#14) the sol. to actuate it. The 12V ones have 2 (#14) contact posts, one is fed + 12V to actuate it & the other feeds +12V to the coil during the start processs.

Simply run up the Gen. & see. A 6V will put out 11 volts, a 12 will put out around 16.

The coil should be marked, but it doesn't matter if you use a 'ballast' resistor.


Good luck.

In addition to those methods mentioned above, you can read the build date on the head casting, 6 volt engines ended around '55, but that's not entirely cast in stone. The generator, if Delco, will have a red oval tag if 12 volt. There are very few solenoid starter 6 volt GMC engines (228-302) out there, but they are out there. Flywheel ring gear is 139 teeth if 6 volt, or 168 teeth if 12 volt.

Thanks for the replies.

The truck was a stripped 1954 or earlier dual wheel flat bed. The engine is a 302 with a front center mounting plate (foot) but has studs slicking out on the sides in front which I presume is for side engine mounts. Carb is a Stromberg 2 barrel. Block casting number states 1955 or newer.

Starter has lever actuator on top with linkage going across the bellhousing. There is no solenoid. Is this the setup for a floor mounted starter switch?

So I guess the truck had an engine swap and the engine has 6V electrics? I’m trying to plan ahead when I install the engine in a 1937 chevy sedan.

The 6V starter, flywheel & clutch assembly will be okay unless abused in mass. Remember it was designed for commercial use and worked well for decades here in America hauling heavy loads.

The 6V coil will be ok too. Just use the ballast resistor like the 55-59 trucks had.

The rest make 12V as you wish. Most use the 'one wire' alternator.

Good luck.

John, I think he's gonna have touble running the big truck clutch assembly on the stock 302 in his '37. That bellhousing will be too big I'll bet. He'll need to snag a smaller bell housing off a 228-270 for an 10-10 3/4" (+/-) clutch assembly would be my guess. The 302s came with an 11 1/2" clutch assembly and a bigger bell housing for the Clarke 5 speed transmissions. So I don't think that will work for him in my experience.

The early 11.5" clutch will fit in the smaller engine bellhousings. True, the early clark bellhousing was a little larger on the top to clear the clutch. However, you can either grind a relief in the bellhousing or pre-compress the pressure plate when the clutch in installed. BTDT. The later bellhousings are much, much larger. It will be obvious which you have.

Thanks again for the replies.

So my plan is to put the 302 into the '37 chevy sedan and change to open driveline. The '37 has complete running gear, I also have the drive train from a '57 car with 6-cylinder including 3 speed OD, a separate saginaw 4 speed, some '61/62 1/2-ton PU bellhousings/flywheel/clutch parts, as well as the 302 bellhousing flywhell and clutch.

I'll use the '57 car rear axle which I believe is nearly a bolt-in to the '37 and the saginaw 4 spd or maybe the 3 spd OD. Not sure what bellhousing/flywheel/clutch combo I need but I certainly have lots of parts.

I guess this post should be moved to the drive line form?

Just e-mail 'Gearhead' he has photos & all the info.