Stumped - Tight crank

[NateJD]

Deere guy here working on an 8N sidemount. My aunt got it hot and cracked the head and the block. She found me a used block and a rebuild kit and I got the sleeves in it. Valve train is in. Problem is with the crank. I can torque the front and middle main bearing caps and it's fine but as soon as I torque the rear cap it locks up so tight I can't turn it with a breaker bar. The crank has been turned .010 under sometime previously and I have .010 bearings. I reused bearings from the old motor. First I put all caps and bearings back where they originally were. Tight. Then I tried caps that came with the block then bearings in different places. Every combination I could and it's still tight. I used green plastigauge on the rear main and clearance is .0015, in spec but on the tight side. Everything I have tried is without other caps on, just the rear one. No burs on any bearings or crank. I'm at a loss on this one. Aunt is getting anxious cause the grass is growing. What in the world would cause this crank to tighten up like this? I'm about to order new bearings and try that based on what I hear here. Thanks for any help. Getting frustrated.

 

[Mdparrott]

(quoted from post at 16:48:04 04/13/16) Deere guy here working on an 8N sidemount. My aunt got it hot and cracked the head and the block. She found me a used block and a rebuild kit and I got the sleeves in it. Valve train is in. Problem is with the crank. I can torque the front and middle main bearing caps and it's fine but as soon as I torque the rear cap it locks up so tight I can't turn it with a breaker bar. The crank has been turned .010 under sometime previously and I have .010 bearings. I reused bearings from the old motor. First I put all caps and bearings back where they originally were. Tight. Then I tried caps that came with the block then bearings in different places. Every combination I could and it's still tight. I used green plastigauge on the rear main and clearance is .0015, in spec but on the tight side. Everything I have tried is without other caps on, just the rear one. No burs on any bearings or crank. I'm at a loss on this one. Aunt is getting anxious cause the grass is growing. What in the world would cause this crank to tighten up like this? I'm about to order new bearings and try that based on what I hear here. Thanks for any help. Getting frustrated.

Any chance that one set of bearings isn't .010, since you're reusing the old bearings? Mic the thicknesses and check.

I've heard of people turning one journal and only replacing those bearings.

 

[NateJD]

That crossed my mind too but all the bearings are marked .010 and the crank wasn't tight in the old block. Good thinking and I will double check for sure.

 

[Den N Ms]

NateJD.You have to use the main caps that cane with the new block,also the front main/oil pump that came with the block.

 

[ZANE]

You definately can't mix main caps from one engine to another. No matter what engine you have. Each main is machined for that particular engine and
not other will work.


Zane

 

[rustred]

as mentioned,.. caps have to be installed in there original position! caps and each block is one unit and line bored as suck. if u have things mixed up and cant get it figured out then you must line bore that block. to get the correct bore clearance. the undersize bgs. cant be a problem cause this would cause you to have excessive crank clearance on the turned crank, not tightness.
any time there is a block missing its main caps, its garbage.

and... the mains and rod caps are to be numbered if not done so to prevent mix up.

 

[ASEguy]

Rusted has it. The main caps will literally fit the other block, but will not work unless they are line bored to the other block. If you switch them back and it is still tight, then you need to have the caps all torqued to spec without the bearings and put a straightedge in the main saddle and check for saddle alignment. Max. is .0015. Also main caps MUST go back in same position AND same direction. I always scribe mine with an arrow pointing forward like the pistons. While we're at it rod caps must go back in same position (same rod) and direction as well.

 

[TheOldHokie]

(quoted from post at 19:48:04 04/13/16) Deere guy here working on an 8N sidemount. My aunt got it hot and cracked the head and the block. She found me a used block and a rebuild kit and I got the sleeves in it. Valve train is in. Problem is with the crank. I can torque the front and middle main bearing caps and it's fine but as soon as I torque the rear cap it locks up so tight I can't turn it with a breaker bar. The crank has been turned .010 under sometime previously and I have .010 bearings. I reused bearings from the old motor. First I put all caps and bearings back where they originally were. Tight. Then I tried caps that came with the block then bearings in different places. Every combination I could and it's still tight. I used green plastigauge on the rear main and clearance is .0015, in spec but on the tight side. Everything I have tried is without other caps on, just the rear one. No burs on any bearings or crank. I'm at a loss on this one. Aunt is getting anxious cause the grass is growing. What in the world would cause this crank to tighten up like this? I'm about to order new bearings and try that based on what I hear here. Thanks for any help. Getting frustrated.

You cannot use the caps off the old block on the replacement. I know you said you used the caps that came with teh new block but they may not be the correct ones and/or they may be in the wrong position.

Time to check the crankshaft for bend and the block bore for straight and round.

TOH

 

[NateJD]

Thanks everyone. Looks like it's off to the machine shop.