I have assembled my first engine, 383CI, after brought back from the machine shop. The first 6 pistons went in, torque to spec engine still can turning by hand, but when the 7 and 8 pistons installed, it's can hardly turn over even though with 24" bar. Is this normal because the assembly is new or it should still can turn by hand. Thank you

not normal. take it apart and look for a problem. normal break-over torque for a new short block with stock components should be in the 30-35lbft range.

I put a 318 together once and had a similar issue. Seems that somehow the bottom oil ring rail got folded over on #6 as I was putting it into the block ... And almost seized up the whole works

Look for scoring in those last two cylinders you installed !!!

Make sure the rods are oriented correctly on the piston and not binding.

I've had this happen to me too when I didn't install an oil ring correctly.

You said 7 and 8 . Did you turn it after you put one in before the other ? Normally you are turning it some after each piston installed . I hate to say, that if you needed to ask the question, if it was normal to be so tight, you probably should have someone experienced helping you ! There are so many possible errors could have been made. Is a bearing cap mixed up with the wrong rod, or cap on backwards ? Did you check the bearing clearance ? Also check the side clearance between the rod caps.I don't know your knowledge level . There are a tremendous amount of things that can go wrong in an assembly process ! Also machine shops can make errors that can cause a problem . I once had a big block that seized every time I tightened one of the connecting rods. Come to find out, they machined the rod bore crooked, and it was pushing the bearing out the side of the rod bore.

As mentioned there could be a lot of different things causing it. First loosen the bearing caps(both main/rod) and see if you can move it. If not then you need start disconnecting piston rods to find where the problem is. When you had the block bored did you give them the pistons? Sometime there are slight machining differences that the machinist needs to take into consideration when boring.

If the crankshaft rotated easily by hand before installing any rod and piston there is really no need to loosen the main caps during your trouble shooting, remove one of the last two pistons and rods and see if that free the crank up, if not remove the other one and see if you can find the issue
It is ill fitting or a twisted ring probably
Good luck Lets us know what you find, that will help others on here now and in the future

If it's bearing clearances on just that journal, it may have left some marks.

has the thrust bearing been seated? dave ss/ea #1355

make sure you didn't put a rod cap on backwords.

Agree, or the rods could have been installed into the pistons backwards. That would have the chamfered edge to the insides with the square edge biting into the crank on the chamfered outer edges of the crank.