186 Piston size of 94 mm. How much oversize is this? .010 .020 .030 .040. 060 ?

Probably needs to be measured a bit more accurately.

The most common over-bore size for the 186 was 0.060", this is 3.685" which is 93.599 mm.

Next size up is 0.080" (a lot less common) this is 94.107 mm.

Also, piston to bore clearance also has to be factored in & the piston measured at the correct position on the skirt at 90 degrees to the gudgeon pin.

Dr Terry

Edited by user Sunday, 14 August 2016 4:45:16 PM(UTC)  | Reason: Not specified

I wonder how you're measuring that. As Terry said, where and with what you measure it is critical. The bores are usually worn to an oval, and truncated as well so it can be deceiving.
Having said that, .080 is getting up there for a red motor. You can have them sleeved, and maybe you would for an original engine out of an original car, but it's a fairly large investment for a transplant engine. I've heard numbers around $100-$120 per hole.
Better to wait for a standard bore engine to come along, even if they are rare.