[Goat-Racer]

The accuacy is important, but the DBG is not "measuring" the diameter of the bearing bore, it's only telling you the "difference" in diameter between your zero (crank pin) and the bearing ID. Having a DBG that reads down to ten thousanths is nice too.

The bigger problem is that the tiny litle hard ball at the tip of the anvil and plunger, combined with stiff spring pressure behind the plunger can literally dig a trench in the bearing and give you a false clearance. It's not always much, but if your on the edge, it can bite you. They work fine for measuring the hosing bore in the block itself because the iron is hard enough to not be an issue.
Just be careful.

[ANDYA]

I recetly purchased a Central dial bore gauge. It's made in the US and reads to the 10 thousands. When I received it I took a 2-3" Starret mic, opened it to 2.500 and zeroed the bore gauge inside it. Then I opened the mic exactly .002 and rechecked with the bore gauge. It read exactly .002 so I figure it's accurate. The biggest PITA is trying to zero the bore gauge inside the mic as it takes a little practice.

[ry57pont]

thats a good idea, i just had my etalon 2-3" cal'd i will use that as my standard. Thanks - RB

[Goat-Racer]

I have a soft jaw hobby vise that I use to hold the mic when setting the dial bore gauge. Spend some time and get the feel.
What you learn when you start chasing ten thousanths (.xxxx") is that temperature and personal measuring techniques are really important. Then you have to step back and realize that your really splitting hares at that point and you need to give yourself a window of tolerance. It's a fun challenge!

Here are a few pics of the two Mitutoyo dial bore gauges that I use. The "511" series (bright finish) was a $100 ebay deal, while the "545" series (black finish) was a new purchase that a buddy and I split to ease the pain. Way more spendy, but still half of getting a basic Sunnen gauge setup. You can see how the 511 series, like most of the inexpensive gauges out there, has a very small steel ball at the end of the plunger (between the two guide wheels). The 545 series has a very gradual radius on the end of the plunger, and has about half of the preload spring pressure behind it. It glides over the bearing surface without leaving a trench behind.

Hope this helps!

[440GP69]

Also "not a huge deal but if you wanna be anal" make sure the lill ball or anvil is facing up so gravity has no effect on your measurements and measure the bearings 90 degrees from the parting lines meaning straight up and down as this should be where your tightest clearance is fyi
I Want a Gage that measures all 5 mains at the same time to see how straight the mainline is, yes you can use a machinest straight edge and feeler guages but i want a more advanced tool but i also want a hand held sonic tester so i guess i can keep on wishing LOL