Okay so I'm getting a 305 out of my buddies 90' camaro RS that has about 175k on it and sticking it in my 92' gmc 1500 (since it's coming from a 90' camaro I figured it would be okay to post here), and we decided to pretty much rebuild it before swapping it out with my current 4.3L and I was wondering if anyone could help me as to what main/rod bearing size I should get?

The original bearings seemed pretty scored and the engine has 175k miles on it so I wasn't sure if I should get undersized bearings or std? We also used 2k grit sand paper on the journals to get the grit in the middle off and shine it up some, although I doubt that would make a .010" difference Thanks for any help that can be provided, or explain the purpose of undersized bearings!

 

Take the crank to a machine shop. Have them tell you they will turn the crank down to, then you can order the bearings.

You can't do what you did to the crank and expect the engine to last more than a few minutes.

 

Oh, well what exactly did we do wrong? I was hoping we could just take out the crank and replace the bearings, didn't know it would be necessary to machine it since I took it out.

 

Crank journals are precision machined parts. If the bearing scored the crank, you won't be able to clean that up by hand. Sometimes you can get by with 0.001" undersize bearings with even, minor wear, but if you've already taken sandpaper to them, most likely they aren't properly round or straight now.

At least take the crank to a shop and have them evaluate it. They will have a better idea being able to measure it in person than we could from a distance.

 

Oh no I mean the bearings seemed a little scored, the crank looks fine. I only used 2k grit sandpaper a little to clean it, soaked up some carb cleaner with it and wrapped it around and rotated it a little to make it clean to examine it a little better.

I used a mic to measure it and all the bearings I see say like "std" or "0.010 undersize" and don't list the actual size so that's why I was asking.

 

dont do it 305 a crap just junk it dont spend money on it your best bet is to find a 350/400 the are better motors i think you should go 350 alot cheaper to make go fast then 400 and the 305 get worst when they are rebuilt

 

www.mortec.com lists the standard journal sizes.

 

Sorry for bumping up an old thread.

I am also interested in standard 305 crankshaft journal sizes and found this thread but the site is no longer available that five7kid mentioned.

Any chance of getting the information?

 

I'm glad the thread was brought up...
I'm rebuilding a 350 and the crank is already in BUT, since I know little about all this and my friend is leading the way I did as he instructed which was to use Scotch brite pads on the crank to "clean it up". There was no scoring of any kind but I did give it a decent rub down.
Was this a "no-no"?
It's a mild mod to the 350. Nothing extreme at all. Does that matter??? Probably not.

He's done a few rebuilds so I felt comfortable trusting him on all of the help and guidance. Do I have to tell him that I want to start over with the bottom end? It could be an interesting development in the friendship LOL

 

The main journal was 2.45 and rod was 2.10 if I recall as stock. That was a couple months ago I'm not sure if it changed any time between when they added roller cams or not.

And what I did didn't hurt my crank. The engine is still running strong after I worked out getting the right prom. I think I got like .001 undersized bearings though since the crank had ~180k miles on it before I got a hold of it. Of course what I think five7kid meant was that you shouldn't try and "machine" a crank with sandpaper. I was simply cleaning mine and it didn't hurt it.

 

You may also find when you need to get the crank worked on it's cheaper to just buy a re-manufactured crank kit than have the work done. Around here it's about $50 to $100 cheaper than having the work done.