machining a split part and trying to measure it

Ok so i feel really dumb asking this question. Several of us are stumped on this one.

We are machining a split pump that has larger bores on the inside than on the ends. The end bores are too small to reach through to measure the larger internal bores. There is a .030 gasket that goes between the halves. I would normally machine each half to the radius dim including the half the gasket thickness. The probe in the machine is checking from the split line face down to the bottom of the bore. We are taking that number plus the gasket thickness to come up with the bore dimension. The issue is that the CMM does not agree with us. In fact the CMM says the bores are .010 too large. the small bores measure small when we do the math on the halves yet when you put them together and take a hard measurement they are perfect. Again i cant get in side to check the hard measurement. This is making me feel like an idiot. lol. any ideas of what Im missing

Might just be a matter of language, but you want to cut the small bore halves to exactly the radius, but shallower by half the gasket thickness. If you actually cut them to a larger radius, then they will indeed be too large.

Maybe Reprorubber. https://www.mscdirect.com/browse/tn...ugwuXycQQNJpsVTy4Bycvzlr7M6ndDi4aAmnLEALw_wcB

You should allow half the gasket thickness.
Could you reach in there with telescope gage?
Caliper check up at the split line should get you close enough to know if the CMM is right.

Try a dial bore gage:

Bore Gages Series 511-with Micrometer Head

put it inside and assemble the housing around it.

if you want to check the radius of the segment, you could use gage pins and a height gage to check what your cmm is telling you.