OK. on square channel cut across the bolt hole on the mating face of the big end cap and the slight step to the inside edge.
I was thinking of deformation purposes in regards to the ovalness bore
due to stretching
1. The channel cut does not present a uniform reduction in material, because the dowel goes through it. You can see the dowel hole and everything.
I do not think that the engineer would want to contend with that. So It can be inferred that the deformation is so small ACROSS this area that it is trivial and so the engineer decided that adding the dowel in that spot will not affect the ovalness of the bore. Notice that tension on the caps will not appreciably increase the diameter of the bore acrros at this point because it is perpendicular the load. I Notice that Mr.G said the rod is 38mm across and 37.82 up and down. So I can only assume that the deformation is being controlled not
at where the mating surface is but through the actual hoop of the cap
If you look closely you can see the outer edge of the mating surface is slightly higher than the inner edge (the side nearerst the bore).
I think that when this is bolted down, the higher outer edge of the mating surface forces the outer fibres of the hoop
into compression. So they are essentially pre-loading the outer "fibres" of the hoop itself into compression. When the connecting rod is on the tensile stroke, this pre-load counteracts the tension. So the diameter in the vertical direction does not grow as much.
This is how I think it works..
THe actual channels now.. I wonder if they are for a measuring instrument such as a feeler gauge or something to check how crushed the big end is upon assembly?