Crankshaft will not rotate

[TechNova]

you sure you got your crank back? Check the crank with a mic.

 

[Erik the Awful]

I haven't seen one yet that didn't have the main caps marked, but this is GM, so there's probably some weird ones floating around out there.

That does look awfully dry. Did you put any lube on the bearings?

If it's lubed, I'd take the caps back off and check each journal with a dial indicator. Or take the crank to the machine shop and have them check it for straightness.

 

[brian c lindsey]

are you sure you got your crank back from machine shop, not hard to get them switched

 

[Hipster]

I haven't seen one yet that didn't have the main caps marked, but this is GM, so there's probably some weird ones floating around out there.

.

I don't know whether it's a year span or based on which foundry kind of thing but the pic of the cap on the 91 block I posted has no indicator for which journal it goes on. This was not the first one I came across so there's some out there. I don't exactly remember but wanting to say the other one I had the issue with was also an early TBI block.

 

[Postmech]

It sounds to me they gave you a different crank like Brian said. Most machine shops will stamp on the crank the amount they grind off the crank . Like M .010 R .010. Check that the bearings match the crank.

 

[Armalite15]

The only suggestion I have that I didn't see mentioned is the possibility of the main bearing set being for a crank with an oversize thrust. Not common but it happens, if you have the oversize (width) bearing that might explain why it will spin before you torque it.

OK reading is hard see you used same bearings, I'd say they may have given you wrong crankshaft as well.

 

[L31MaxExpress]

OK Hoss, I been working on these trucks and others for the last 40 plus years and that includes time as a GMC service tech, a Chevrolet tech, a Peterbilt service tech and an International service tech
I have yet to see an engine that did not have the caps numbered from the factory. Caterpillar, Cummins, Detroit Diesel, International/Ford all number their main caps as does Chevrolet/GMC.

The main reason that the caps are numbered in the first place is that when the blocks are cast they must be machined to size which includes line boring and then disassembled so that the rotating assembly can be installed.The numbering of the caps prevents the issue that the OP is having on the assembly line, Hoss.

NONE of my small blocks have ever come from the factory with numbered mains.

 

[L31MaxExpress]

One other possibility is that he did not properly seat the thrust bearing with a deadblow. Thrust bearing misalignment will cause the crank to be difficult to turn when the caps are torqued.

With the main cap bolts snug but not torqued, take a rubber dead blow and smack the crank foward and backwards with moderate force. Then torque all the caps.

No deadblow, use a 2x4 and a ~2 lbs hammer. Use the wood to soften the impact preventing damage.

Always use acetone and a lint free rag to clean the block, caps, crank, and bearings. You want everything super clean and to handle those parts with clean gloves. Even a small bit of debris can distort the bearing in the bearing saddle. With the bearings oiled with engine oil and the thrust bearing properly seated you should be able to spin the crank with a single finger. If you cannot you need to find out why. Otherwise you will smoke a bearing or bearings very quickly and possibly destroy the crank or block.

 

[thinger2]

You either have a bearing in seriously cockeyed with crap under it or,
They bent it when they machined it.
Easy to do.
And it doesnt take much to make it bind.
Its either that or they gave you the wrong crank.
im gonna go with they bent it

 

[VIKING_MECHANIC]

The main caps have an arrow stamped/cast in to them indicating the proper orientation. The arrow points to the front of the engine. The caps are also numbered 1 through 4 with 1 being at the front of the block.

Also the bearing locating tabs in the cap must be on the same side as the ones in the block

I know that the arrows point to the front of the engine but in my case I didn't see any numbers stamped on the caps. So I stamped them and the corresponding spot on the block with the same number.