Peterh337
The first engine that had exhibited this problem was a Lycoming factory rebuild, the others were overhauled in the UK.
27/09
It is not a piston pin plug problem but one of cylinder becoming ridged at the lower end of the area swept by the piston rings, as the piston pin plugs pass over this step they have small chips removed this becomes very evident when the oil filter is cut open at maintenance checks.
The oil cooler thing mentioned above has a ring of truth about it as the lowest time engine that had this problem had it appear after just under 300 hours, the aircraft had been doing a lot of night training flights and the OAT was some times -15C or below.
The only positive thing to come out of this is that the customer support from the UK Lycoming agents has been very good, they too have suggested that this might be an over cooling problem.
Last edited by A and C; 6th April 2013 at 13:35.