Measuring bearing clearances

[chilly460]

In the past I’ve had machine shops measure clearances and I’ll assemble, figured I’d learn a bit and bought a Fowler bore gauge and working on mains on my ratty 352.  I’ve used a dial bore gauge before without much issue, checking cam bearing and lifter bores.

Issue I’m having is on several of the mains with King bearings, I’ll see say .0026 near the parting line, move around 1/2” around the bore, see .0019”, move another bit and see .0020”.   I’m seeing .0020 of variance on the rear main.

Issue is I havent used a .0001” tolerance dial bore before so not real confident it could even be this far out.  I can repeat the numbers within reason though so don’t feel like it’s technique, although I’ll say using this dial bore take a steady hand. 

My question is has anyone seen that much variance in a bearing clearance?  I did check for any crud or burrs on the bearings and main bores. 

[blykins]

Always check 90 deg to the parting line for vertical clearance and then move across the feed hole and check for taper. 

When you turn your gauge and measure near the parting line, you should see much bigger numbers.  Main bores should be perfectly round with no bearing in them but bearings have eccentricity built in.

[chilly460]

Will do

[blykins]

Make sure you zero your bore mic in both directions as well. 

[RustyCrankshaft]

I'd also say, that all of the Fowler stuff I've had in the last few years is questionable on quality and I have seen some repeatability issues. If it's off a couple tenths and all the numbers are in an acceptable range I wouldn't get panicked over it, but the repeatability is something to keep in mind. For measuring bearings I usually use a Mitotoyo or Sunnen, makes me feel more warm and fuzzy about it. Or maybe that's because I put my coveralls on inside out again?

[Ranch]

If you are on a stand you might want to roll the block over to keep the bore gauge so the anvil and plunger are always reading in a vertical plane.  This kinda makes gravity your friend ....JMO