How tight should center main bearing be?

[rand]

I'm re-assembling the L24 out of my Series 1 240Z and just tried dropping the crankshaft in.  It dropped in with a tiny bit more encouragement than I expected, but that center bearing was so tight that I couldn't turn the crank once it was in.  I pulled the crank back out to investigate, and that bearing came with it!  It was on so tight that I had to lightly hammer it off with the butt of my mallet to get it back off.  I assumed that the bearing would have just slipped onto the journal rather than needing to be forced like that. 

 

My crankshaft was ground down by 0.25mm, but I can't imagine why that would make the thrust surfaces tighter.  I measured the center bearing width and it came out to 32.12mm, but I have no idea if that's nominal or not.  I couldn't get a good read on the crank width at the center journal with my calipers.

 

This is my first time building an engine, so any advice is appreciated.  Is this kind of interference fit expected here, or should I send my crank back to the machine shop, or just order new bearings?

 

Thanks! See pictures below.

 

The box that my bearings came in.  These were provided by my machine shop.

 

Caliper reading on the width of bearing.  Notice that the back of the bearing is now scuffed up.  When I tried turning the crank one way, the bearing tab prevented it from rotating. When I tried to turn it the other way, the bearing just rotated with the crank and scuffed a little material off its back as it went.

[rand]

I just read ahead in my Tom Monroe book, and he says:

 

Quote

If, by rare chance, end play is under the 0.002 minimum, the thrust-bearing flanges will have to be thinned... To increase end play, thin the thrust bearing's front flange with 320-grit sandpaper on a flat surface. 

 

Looks like I'm just one of the rare unlucky ones.  Has anyone out there successfully sanded down the thrust surfaces on their bearings? Any advice? 

[rand]

For anyone who ends up with the same problem, here's an update:  I just talked to my machinist and he said that this is a common issue.  Apparently bearing manufacturers sometimes oversize the thrust surfaces with the expectation that you will be resurfacing and removing material from your crank during the rebuild.  This is usually indicated in the catalog, but apparently was not for my bearings.  You can get them down to size by laying a piece of ~400 grit sandpaper on a piece of glass, spraying some WD-40 on and sanding down the front surface until you get the clearance you need.

[TimZ]

Read through this thread a couple of times for some great pointers on exactly the part of engine assembly you appear to be venturing into.  The title is misleading - they start off talking about the Kameari tensioner and then spend the rest of the thread talking about how to properly assemble the engine.  Great advice from some really knowledgeable builders.