I had my 1950 239 flat head head rebuilt by a guy in town here, bored .020 over, turnd crank .010 under. he put it together (short block)
Got it in hooked up starter and it would bearly turn over with a new 6 volt battery. Put 12 volt to starter and it turned over a little better but it drained down too. Ok pulled out all the plugs put some 3 in 1 oil down cylinders, let sit over night, cranked it over with plugs out and it seamed to turn over ok. Put 12 volt to starter and it turned over good, pretty fast.
Put plugs back in and same issue, will not hardley turn over. Took starter to shop and they checked it and said it was fine, nothing wrong.

What do I look for now??

 

3-in-1 is not "engine grade" oil, don't use that. Your engine is going to be very tight with new rings, tight bore clearances, tight new rope seals, etc. It sounds like your starter may be weak, but if you get the battery all charged up, fuel in the carb, etc and fire it off, it will loosen up noticeably in 10 minutes' running. It will still be tight until you get it fully broken in, which could take 1,000 miles. Best thing is to drive it, not idle it in the garage. Did you re-use the original cam? Are the lifters new or re-surfaced? If any of the valve system is new, you want to get it up to 1500 RPM for at least 10 minutes right away, to break in the cam/lifter surfaces. You need the higher RPM to sling oil up onto the cam.

PS if there is a warranty on the motor, you should report this situation to the shop ASAP, and follow their advice.

 

Are your battery connections to the starter and solenoid clean and tight?

 

Both replies above are spot on. I'll ask if the battery cables are large enough? Or are they common off the shelf stuff designed for low displacement engines starting on 12V?

 

Thanks for the feedback.

Size "o" for cables, only 4 new vales and seats. ORG cam and lifters used.
I'll double check grounds and connections. I'll contact shop tonight see what they say.

Thanks

 

The rope seals especially can be very tight until they get worn in and soaked thoroughly with oil.

The other thing is that it's getting colder out. Typical pre-assembly lube gets to be like 90wt when it's cool. Spinning it with the plugs out until fresh 10w30 gets into the bearings will help.