I'm in the process of rebuilding a 355 for my brother's Camaro. We got the block and crank back from the shop and ready to assemble. My question relates to plastigage vs micrometer. This is the engine's second rebuild (Rebuilt by GM 4000 miles ago before previous owner got it, sat 6 years, so we are rebuilding it before using it). The crank has been ground a total of .030" on both rod and main journals. I have not officially measured the journals or the bores the correspond to. My question is whether I should mic them (I know I SHOULD but I dont have a mic) or just plastigage them before final assembly. I know plastigage isn't necessarily accurate, but I also noticed +/_ .001 bearings aren't readily available for 030" over bearings, so is there really anything I could do about adjusting clearances to the additional accuracy of a micrometer, or am I pretty much stuck with the clearances I end up with anyway?
What would be the consequences of clearances being a little tight/loose?
We want this engine to last a while.

 

IMO what you should do is get a fresh used cam, there's no sense in going 30 under when a good used, straight cast crank is so cheap. A quick polish and you'll be in business.

The measuring, whether with PG or a micrometer isn't to measure if you need a +/- .001 bearing, it's whether the clearances are in the acceptable range, if it's off either a little more has to come off or the crank is toast (or needs even more undersize)

You're stuck with what you end up with

 

But rather than used........... a New Cast "Steel" Crank is $170.oo
http://www.summitracing.com/search/?...ankshaft&dds=1
and a 4340 Forged Steel unit is $540.oo whether it's a 1pc or 2pc... 3.48"or 3.75" stroke
http://www.summitracing.com/search/B...U&mbid=HP50R44

When you consider what all the parts and machine work is worth, why should you worry about the crank now?

Are you planning to spin it high? or throw juice at it?

 

dont let all of that scare you a stock crank with .030 rods and mains can actually be stronger and more reliable than a stock std. rods and mains if machined with a large fillet radii. You will be fine using plastigage just make sure that the clearances are good. If its on the small side you can remove the top coat on the bearing for clearencing some times that can be enough and will not hurt reliability ive done this myself many times. If its on the larger side then that can pose a problem with oil pressure but if the work was done at a good machine shop you should be fine.

 

I'm gonna try to get my hands on a micrometer and bore gauge, but if I can't I will plastigage it and try to get the clearances as close to the tight side of the spec that I can. Ive read plastigage usually reads too tight. Then I'll spin it by hand and make sure it doesn't feel too tight.
It's probably never going to see Nitrous or a supercharger or anything.
Just a set of heads, a street cam, and carb and intake.

 

Fillet may be improved depending upon the machining but journal overlap certainly isn't. IMO there really is no reason to even run a 10 under crank with how cheap a stocker is nowadays.

 

well, we're not replacing the crank unless we have to. It's already machined and ready to go.