VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 48 motor won't turn

I have had a 48 motor rebuilt. Sat it in the frame and turned it with a bar. Quite firm but it did turn.Put head on without plugs.Drove oil pump with power drill and oil came up to head. Fitted starter motor and fresh 6V battery. Will not turn. Fitted 12V battery and it turns well enough.
What do I do now? Continue on and start it with 12V and hope that it loosens up or do I pull the motor and have it all checked over again?
All suggestions welcome;
Terry H

If the starter isn't up to par,battery cables too small,battery of smaller capacity,battery low on charge, or poor connections its not uncommon for a fresh rebuilt engine to not turn over with 6 volts.Years ago some of the mechanics made them so tight it was necessary to push the car to get it started.This was before 12 volts.
After runnig at a medium speed for a while you should notice a marked improvement - except it will still turn over hard when hot....After about 1000 miles it will be back to normal.
If you do let it sit and run keep engine speed well above idle so as to throw the oil up on the cylinder walls.

Gene, I remember back in the 50s a new Chevrolet came with "Break in" oil and it was run 500 to 1000 miles as I remember, also was used for a "rebuilt motor" What was different about the break in oil than regular motor oil, was it the viscosity? Was this supposed to seat the bearings and rings better? I was wondering if I should consider using a different oil in a new overhauled 53 powerglide engine.

the original break in oils were just a good #10 oil.They wanted a "thin" oil to be used for better flow to the tight places.In the later years the oils were fortified with anti-scuffing agents tc. to prevent damage during break-in.
Probably the best break-in oil today would be the new 5W-20 oil that some makes recommend for all service.
Yes- early on we changed oil at the first 500 miles as per factory...actually in the dealership that I worked at they recommended it at the first 350 miles -for both new and freshly overhauled engines.
In the '70's the factory recommended leaving the oil in for the full normal oil change interval (3000 miles) as the oil contained "special break-in additives"...if it was changed sooner a can of GM "EOS" should be added.It is an engine oil supplement that contains the additives.Still sold by GM today and recommended for fresh engines and new camshaft installations.