Morning all,

My crank was ground 0.030 under at some point. Found the last full set of 0.030 under conrod bearings in existence it looks like. Put them on, everything good until bearing #5. Anything past finger tight torque on the nuts seizes the whole motor. Ordered new plastigauge to investigate this one but was it common to grind 5 journals to 0.030 under and leave the #5 journal original? Haven't had a lot of time recently to tinker, back to back to back weddings and work travel but would that be a realistic scenario or do I have a bigger problem to address?

Alex

 

I'm guessing this is a six cylinder engine?

 

Sorry, yes. 226H

 

It was sometimes a practice to turn all mains or cons and vice versa, but to just turn some of each is a very poor practice, and was probably performed by a midnight machine shop.

 

You are using assembly lube....right??

Some long cranks can have a very small bend in them, so try mounting #6 and then come back to 5 and see if it clears up. Is the thrust bearing on #5?? that could also be binding a bit until you smack the crank back and forth a few times. My guess is you don't own a mic??

 

Hopefully get some more data when I plastigauge.
Yep, lube isn't the issue. I can spin the motor plenty fine with #5 on but not torque near spec. It's when I get above 15-20 lb ft that the whole motor locks up dead. Even tried rotating the motor every 5 lb ft increment to make sure nothing was binding but no, hits a very hard limit and stops dead.

 

I havent heard of leaving one journal stock, but I have heard of a box of bearing shells having a set or two of the wrong size shells in it. The shells are usually marked on their backs.

 

Thought of that. Swapped it out with another bearing I bought from Egge 0.030 under..same problem. Unless two bearings were both mismatched on separate orders from separate shops, I think the issue isn't the bearing being wrong in the box.

 

Ok, here's what I would do. Remove the crank and bearing inserts and then torque down the bearing caps and check the ID with an inside mic. Also mic the crank journals. It could remotely be a line bore issue.
You can also compare the torqued down cap ID with the new and old bearing inserts.

 

If you still have the old bearings check to see if they have sizes marked in their backs ?

 

Alex, You need to pull the crank and mike all the journals to see what you have. Chevrolet is notorious for grinding one journal odd on new engines if they have one journal messed up in the manufacturing process. The previous rebuilder of your engine may have done the same thing. The only way to tell what you have is to mike the crank.
Mark

 

Are you putting in new bearings without turning the crank?

 

It could also be the rod needing resized if it seizes like that. If it's out of round even slightly, you'll have problems.

 

Everything turned perfectly when I took it apart but the old bearings looked a little on the worn side (see rebuild log for pics) so I got NOS bearings. Plaque on the side of the motor says crank 0.030 under. I'll start with the plastigauge tonight and identify if I don't have enough clearance.