OK, so why Mahle / Clevite sell oversize rings then? It is the same fabrication system as the 2.7l?
So it might be but you are not comparing eggs to eggs.
The 2.7 litre engine is old style iron block design, the later V6 is newer generation of alum/alloy block construction.
For reasons of cost introduction, thermal and load stress considerations (amongst other reasons) the alum block design can have much more uniform construction which in turn leads to potentially longer engine life.
By virtue of the design a thin yet very durable coating can be applied to the cylinder bores by electronic flash fusion techniques which has excellent heat carrying capabilities.
This thin coating is about 0.010" thick or (0,025mm). Any attempts to bore it out to a new hole size would redoubtably mean breaking though the coating to the relatively rough parent block or leaving the section so thin that it would simply strip off in service with catastrophic results.
So some pundits might say well make up some cylinder liners and press those in!
OK!
To get the same heat propagation through the new liners as the fused original what would be the interference requirement need to be?
From my experience & engineering dictum it would need to be in the order of 0,004" or 0,01mm.
To get that level of interference "fit" on an alum block there would need to be a lot of heating of the structure to allow a scuff free install and even then using an industrial lube medium like Castrol Illoform would not entirely ensure a uniform fit. Even the activity of heating the block and pressing in of liners would no doubt cause block structure deformation and cracking risks.
That in turn would lead to high block scrappage on repair or high risks of in service engine failure.
I find it frankly hard to reason with this old fashioned lingering idea that today's engines can be reconstructed.
Many if not all cannot, and the trend has been around for a long time now. BMW have the distinction of introducing it (fused cylinder coatings) in their 7 series 4.4 litre V8 in the mid 90's, and its been commonplace with Asian manufacturers for about the same time if not longer.
MB has just caught up with the rat pack with the OM647.
Really those owners who buy this stuff in the "gah gah" moments at the point of purchase rarely ask what are the cost implications of ownership and service maintenance costs.
Need I state it is incumbent upon all buyers of vehicles (the 906 included) to know the service costs and ask yourself whether you can afford to own the rig and repair it when it goes 'bang" !
It called risk management!
Cheers Dennis