Originally posted by Keyser:
Piston to Bore Clearance
Standard
0.012-0.022mm (0.0005-0.0009in)


Keyser,good info to post. I hope a lot of people copy this stuff. Maybe Lance could put it in a help section.

One note: The above clearance should be
-0.012 to +0.022mm. Yes, that's negative clearance, as in interference. This clearance spec is only valid when measuring the piston with the coating. The target coating is about 0.010mm per side. Now, when we talk about standard pistons at the factory being Grade 1, Grade 2, or Grade 3, that measuring is done before the coating is applied at the supplier. Mahle in this case. The factory is actually building to a clearance of about 0.018-0.042mm ignoring coating. (Yes, I know it's not exactly 0.020mm larger but that's what they build several thousand engines to everyday)

The clearance with coating is really for reference but once the coating is applied, you can't truly measure the piston diameter. It can still be useful and sometimes it's all you've got.