Bore Measurement Technique
 

Gentlemen,

I'm looking to measure the main bores on my case. The case in question, a 1987 930, has a bore diameter specification of 60.020 - 60.059 with the bearings installed.

My preference would be to mic the bearing shells out of the case, and add this to the listed spec above, and check the main bores. For example if I measure my bearings to be 0.500 mm thick, then I'd check my case and make sure the bore is 60.520 - 60.559. Is this an acceptable method?

Or is the preferred and correct method to install the bearings and check the bore with the bearings installed?

I only prefer method #1 as it seems to be a gentler process on the bearing shells.

What are your suggestions?

Thanks
Rich

I've always understood that the correct method is to measure the bores without the bearings and the through bolts torqued, and separately measure the bearings. I'll be curious to hear if anyone has different guidance.

Note that to do the above, you need to have a bearing installed in the #8 bearing web or the case won't line up properly for measuring. Since the #8 bearing has an ID too small to allow insertion of a bore gauge, someone gave me the tip to use a bearing from a 1600 VW type 1 motor. Luckily VW bearings are a lot cheaper than 911 bearings.

Thanks for the suggestion on the VW bearings, and your process on bore measurement.