Is it posible to run a single ring crank up front with 8 gears on the back without needing some sort of retainer on the front chainring ? would the rear mech keep the tension ok ?
Yes I believe you can. Ask Ededwards - pretty sure he runs that on his Vit T. Here's a picture from when it was at the Real Ale Wobble. Not very clear but it definitely is 1 x 8.
i run a 32 up front and 8 at the rear and haven't had any problem to date, i don't have a chain retention device or bash guard on the front either just a stripped down lx crankset. my chain line is set for the center of the rear group, sweet as anything on changing gear.