When I purchased my bore micrometer, it had set me back $80. This was a welcome $80 because the Snap-On version was selling for $400 and that was the same as a new pair of pistons. Unfortunately, an $80 more micrometer from China doesn’t come with instructions. Here is how I came up with my readings (please correct if you know a better technique):

Using my calipers, I measured the initial dimension of the head of the bore mic. There is a spring-loaded trapped ball bearing at the end of the mic flanked by two rollers. Once inserted into the cylinder, the ball bearing is compressed against the spring and moves the dial indicator. This indication is relative. It is important to measure the length of the measuring head first and then subtract the difference of the reading after inserted. This should give you the absolute reading of the ID.

Initial bore micrometer diameter = 3.2325″ or 82.1055mm
1 tick = 0.0005″ or 0.0127mm
Reading on dial gauge after inserted = 3.2305″ or 82.0547mm

After you get everything inserted, zeroed-in, and ready to go, begin by measuring inline with the axis of the cylinder when installed on the engine (the parallel reading). Take 3 readings for each cylinder at the base, center, and top. The top (where it meets the head) should have the most wear if there is any.

To take a reading with the bore micrometer, rock the device back and forth inside of the cylinder and observe the maximum reading on the dial indicator. The wheels should help keep it centered on the surface as you move it. I found it helpful to set the indicator gradations in the middle of the minimum and maximum variations. It seemed as if my cylinders were then either 1 or 2 ticks over, or 1 or 2 ticks under. It helped me keep track as I was recording the readings.

Once you are done with the 3 readings for the parallel axis of the cylinder, repeat in a 90° perpendicular direction. Record the readings and which cylinder you are measuring. This is important when you start determining total wear as the wear of the piston from that cylinder is subtracted accordingly.
Vertical cylinder parallel readings

1. Top (equal) 3.2305″ or 82.0547mm
2. Middle (equal) 3.2305″ or 82.0547mm
3. Bottom (equal) 3.2305″ or 82.0547mm

Vertical cylinder perpendicular readings

1. Top (equal) 3.2305″ or 82.0547mm
2. Middle (equal) 3.2305″ or 82.0547mm
3. Bottom (1 tick under) 3.2310″ or 82.0674mm

Horizontal cylinder parallel readings

1. Top (equal) 3.2305″ or 82.0547mm
2. Middle (1 tick over) 3.2300″ or 82.0420mm
3. Bottom (2 ticks over) 3.2295″ or 82.0293mm

Horizontal cylinder perpendicular readings

1. Top (1 tick over) 3.2300″ or 82.0420mm
2. Middle (1 tick over) 3.2300″ or 82.0420mm
3. Bottom (1 tick over) 3.2300″ or 82.0420mm

From the Ducati Workshop Manual, the specs for wear limits are as follows:

Max taper = 0.05mm

Max out-of-round = 0.05mm

To determine the taper of my cylinders, I took the value of the top readings for both the parallel and perpendicular measurements and subtracted them. This should give me the maximum taper of my cylinders.

To determine the out-of-round value, I subtracted the largest value of the ID of the cylinders from the smallest value. This should give me the maximum difference. Ducati specs the maximum permissable out-of-round value as 0.05mm.

Here is an RSS feed from eBay where you can see the internal micrometer (bore gauge) currently for sale. I got mine from a guy on here for around $75 and it seems worth it if you are going to do it right. It also helps justify spending money on replacement parts.

This is the kind of tool that it would be great if the Ducati community would share. You only need it once, and $75 is a lot to spend only to find out that you need to replace them anyhow. I may look into a shared tool repository. Maybe a map of local specialty tools on Frappr.