Jens,


The ring end gap for full size engines is 0.0065-0.0115 times the bore diameter.
This can be seen in [link=http://www.kb-silvolite.com/article.php?action=read&A_id=32]this Keith Black web page[/link].

Our methanol fuel engines that generally run at a lower temperature should have the gap set at bore X 0.0080, or smaller.

For a 27 mm bore of a typical 15 cc (.91) engine, this means a gap size of up to 0.216 mm is OK.


But I was talking of too small a gap, causing the ring ends to butt together, as the ring heats to operating temperature, causing increased ring friction, wear, overheating and possibly breakage.
If the ring gap is smaller than the bore X 0.0065, or 0.1755 mm, in the case of 'our' 27 mm bore engine, butting could happen.