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What is the best way to determine if a case needs to be bored for oversized main bearings?

BOBC:

The best way is to torque the case and measure with a bore gauge.

Short of that, look at the saddles and run your finger nail over the surface. If you feel raised areas, that's a good indication that it needs attention.
Look for numbers from the back of the bearing being pounded into the saddles.
If the bearing falls out( is not tight) when installed, that also is a good indication that it needs attention.

Hope this helps
Dietmar

Bobc,
Just as Dieter states, checking with a bore gauge shoud be done, but even if the bores check round and to size, I also like to install boring bars that are set up to the current dia. for both the mains and cams. This will determine if the bores are concentric. Even on new cases, I have found on rare occasion that especially the center cam bore can be what I refer to as "swayback", meaning that it has dropped out of concentricity. It is far more common on cases that have gotten hot. Typically, the hotter thay get, the worse the condition becomes. Also, while the case is torqued together, inspect the center bearing saddle seam by shining a bright light from the other end.....if you see light coming through the seam, stop there......get another case.
Mike P.
Peak Performance Racing

what is the stock diameter so I can figure out if my block has been bored?

Roger:

Check you messages

Dietmar

Great points by everone. Note: the usual clearance on mains is .0025. If the bore is out of round just .001, that's 40% of the clearance gone.

Sorry, couldn't resist....

You can tell the case is bored if it is sitting around restlessly. This is common during the off season, especially the couple weeks just before the first race.

Ughhhhh. True though....