Hope this is not in the wrong forum, but I think it is.
How difficult should a crankshaft be to rotate when the bearings caps have been torqued. I am building a motor, and after torquing the main caps, the crank does not rotate in the manner it should. I inherited this motor as a project for a friend and I am not sure if all the parts are right. Thanks for any response!

 

Just to clarify a little, this is a v-6 motor i'm building for a friend. it has a new crank and new bearings. the motor was pulled because the previous owner ran it out of oil and spun a bearing. the block has supposedly been checked by a machine shop and everything is within tolerances. so why won't the crank rotate.
does anyone have any ideas?

 

Do you have oil on the bearings?

Did you check the clearance between the crank and bearings?

If you don't do either it could be too tight and then it will not turn.

Another cringe moment here.

 

"Do you have oil on the bearings?"

The engine is disassmebled. I haven't checked clearences yet, but I will be getting plastigauge today to make that check. I did have assembly lube in the bearings at one point, but I have cleaned it out to check clearances. I have just never seen a crank so difficult to turn in a new motor.

 

use a bearing lube or heavy weight oil on all ther bearings. put some lube on the cyclinder walls as well if you have the rods bolted to the crank. if the rods are not attached, it should turn over by hand. if the rods are on, a wrench should turn it pretty easy. plastigauge should be 1-2 thousands.

 

ok, here's the deal. i have checked the bearing clearences. all are within specs. i cleaned all plastigage off of the crank and bearings, lubed up the bearings and crank real good with assembly lube, put the crank in and torqued it to specs. the crank will not rotate at all. i even tried with a breaker bar on the snout bolt. i don't know what else to do!! anyone think the center line of the block might be off. what else can it be???????

 

well, after much despair, i called the dealer to verify the pn on the bearings and sure enough, they were the 0.005 oversized bearings. the dealer must have screwed up and gave the guy the wrong bearings. just goes to show that you should always question the parts guys to make sure you have the right parts.

thanks for the replies!

 

glad to see you got the bottom of it. easy fix in comparison to some other things that could have been wrong.

:-)

 

Someone care to explain to me how the clearances were in spec with the wrong oversize bearings installed?

 

Same question. Bet the bearings were undersize rather than oversize also.

 

This poses a very good question! Book states clearances should be between .001 and .0014. I know the torque settings were correct and I know what the plastigauge scale readings were. Maybe someone with more experience can chime in here. I haven't got a clue.

note: the bearings were in fact oversized, not undersized. If they had been undersize, the crank would have rotated OK. I think my logic is right here?

 

I guess the logic is undersize refers to the crank journal diameter, and the nomenclature for bearings follows along.

So, if you grind the crank .010 smaller to clean it up, the journals are under or smaller than they were, so the inside diameter of the bearing must also be under or smaller than normal size. Generally this is referred to an an undersize bearing. Of course, the outside of the bearing shell is the same size so the bearing shell itself is thicker than standard size.

If you measured with plastigage and found clearance on all 4(?) mains, you my have a bent crank. An outside possibility is that a couple of main caps are interchanged or even one is reversed. You could possible still have correct clearance on plastigage but main bores are out of line.

Try loosening one main cap at a time, then check if crank will turn. You should find the offending main that way.

My $.02

 

I think you have it backwards there. Nomenclature for a crank and bearings don't follow along.

If you grind a crank .010" to clean it up, the crank will be .010" under than factory/new. This would require an over sized bearing to fill the gap. I personally have never seen undersized rod or main bearings

 

Good point. I guess it depends on where you look as to how they are labelled:

Clevite calls them oversize bearings for undersized journals, but GM Parts refers to them as undersize bearings.

You're right about not finding bearings with a bore larger than standard.

 

It sounds to me like your main sadles need to be line honed and need to check that the crank is bent or not. Also Plastigage is alright to use but if you have everything checked out on the block and it is with in spec I would recomend checking the main sadles with the main caps on and torqued to spec with a good quality bore gage and checking the crank journals with a set of outside micrometers and the diff. in size will be your running clearance.