Update:
Cylinder finally on. Pistons with rings this time. The oil rails needed extra attention since they are very thin and flimsy.
Oil control ring groove in piston only 1.5mm (height). I pinched one ring at first attempt a month ago. I had to order new rings which took time.
ORDER EXTRA RINGS WITH THIS KIND OF PISTONS WHEN ORDER THE PISTONS, JUST FOR SURE
I know now how to do next time.
All rings needed to be checked in bores so end gaps were OK. Recommendation to also deburr the ends so no hard burrs can scratch bore or grip into groove. I used a file and 1000 grit paper to deburr the corners of the gaps.
I should have filed the inner corner of the oil rails much more. The end of oil rails seemed to get stucked into the expander when enter the bores. Mike's billet block have wonderful beveled sleeves that make the pistons to slip in very easy. top ring and 2:nd ring.
The oil rings however needed attention since the oil rail did not enter that smoothly. If stucked into expander it will not squeeze together enough. First attempt when pressing block down, forced oil rail outside and it became pinched. Block off and waiting on the bench.
Today with new oil rail I took my time and wiggled the piston 2-3 so they entered the bores. Cyl block pressed downwards to pistons by its own weight.
I had a mirror to check oil rails during the process.
1-4 pistons were tricker to wiggle by hand. I found another way with a nylon screwdriver inside the wrist pin and I wiggled it forward backward and created heavy vibrations. Block with its bores just vibrated down over the pistons without hammer on it by hand.
FINALLY OK! Verified by rotating crank some turns and checked the oil film in all bores with all pistons at bottom center. No marks or bad sound...
I searched for one-piece oil ring when I pinched one. It was really tricky to test mount pistons in bores on the bench.
I hope this will help others with similar pistons and thin railsI'm sure that these thin oil rails will be much easier to mount if the inner corners of the ends are filed down in a good angle and make it impossible for the ends to hook into the expander and not glide in. The rail is not deep so it is not much in the groove keeping it in place when not completely compressed.
My other experiences of oil rails are, 736 OEM, 3 models of 836 (same type of rings), 900 67.5mm rings. All these just sank into the bores without any problems and no attempt to leave groove. The beveled sleeve did it by itself.
These newer type of pistons are different with the thin oil rings, tricky but possible whitch patience. see photos.
EDIT: As You can see I had only 4 cyl studs when mounting the cyl block. The inner 4, 2 of them with O-rings. Easier to do the rings without studs.
When cylinder was mounted and crank rotated some turns to verify pistons Ok and oil film in bores looked fine, the other studs went in and tightened.
