: Do I need a new crankshaft? :( pic inside



smooththg6969
05-30-10, 06:45 PM
Well I have been going through an old northstar motor I have . Im doing an halfcase reseal and the head gaskets. upon removing the half case and visually inspecting the crank I noticed it has some some grooves worn into it. The oldschool side of me / shallow pocket side says to take it to a machine shop and let them polish it for me. But a voice deep inside of me says get a reground crank with oversized bearings. I just lost at the moment and wanted you guys opinions. pics below

http://i125.photobucket.com/albums/p70/smooththg69/Picture012.jpg

http://i125.photobucket.com/albums/p70/smooththg69/Picture005.jpg

http://i125.photobucket.com/albums/p70/smooththg69/Picture013.jpg

Submariner409
05-30-10, 08:04 PM
GM does not want you to grind the crank and GM does not supply undersized bearings. See if Clevite or FederalMogul has a .002" undersize bearing set and have a shop polish the journals.

Really, that journal, if it mikes to tolerances, is fine to clamp in a new bearing shell.

Wait a minute..........Is that the crank journal or the outside of a spun bearing shell ??

dkozloski
05-31-10, 03:32 AM
A Northstar crank is not regrindable. The journal radii are cold rolled. This cannot be duplicated in the field. If reground the crank will surely break at a journal from fatigue.

Polish the crank by wrapping strips of 400 or finer wet or dry paper with a little solvent on it around the journal. Wrap a piece of clothesline around that and work it back and forth by pulling on the ends of the clothesline. More important than the fine grooves you have in the journals is the dimensions and roundness of the journal. A good automotive machinist with a set of mics can tell you all you need to know.

Submariner409
05-31-10, 11:29 AM
dkoz, Take a hard look at his pictures and see if you don't get the impression that's the outside of a spun bearing - there are even indications of the shell welded together.

I may be missing something, but the journal edge radius looks all wrong.

smooththg, Send some pics of the other journals.

smooththg6969
05-31-10, 05:20 PM
Its the journal Sub, thats some solvent residue that came out of one of the oil holes that I believe your referring to. I try and post more pics later.

dkozloski
05-31-10, 07:49 PM
dkoz, Take a hard look at his pictures and see if you don't get the impression that's the outside of a spun bearing - there are even indications of the shell welded together.

I may be missing something, but the journal edge radius looks all wrong.

smooththg, Send some pics of the other journals.
That crank has rolled radii on the journal that makes it look undercut. That's why you can't regrind the crank. The rolling has to be redone to prevent fatigue cracks and nobody is setup to do it in the field. Welcome to modern motors.

Submariner409
05-31-10, 08:28 PM
Well, hell.............I was looking at the weird discolored patterns on the journal............ In that case he could just polish the journals with crocus cloth.