I am coming round to thinking that they are overall a decent bunch of guys and I just had the monkey of the pack build the bike.
They're the same as every store - they want to sell bikes and them coming back with problems due to poorly skilled builders hits their bottom line. I dare say if the manager knows what's gone on, the guy doing the swap/change will be their most experienced/best builder and it'll be sorted so you're not returning again.
As you've probably guessed, the original builder cross threaded the pedal when putting it together, didn't notice/care (or have the experience to recognise it) and weakened the threads in the crankarm. When it went back they retapped the crankarm to get the pedal to fit properly, which worked but it was weakened so much previously that the threads have now stripped. The only real solution is to replace the whole crankarm. They obviously don't stock the exact replacement Suntour part so are fitting a compatible Shimano part.
I believe the rest of the Marasa drivechain is Shimano (9-speed?), some websites list the M361 as 7-8 speed but fundamentally it should be ok as 7-8-9 speed are generally compatible.
CRC do list it as 9 speed, so might be different conflicting information floating around about it. Someone else may have some actual experience and better knowledge of course...
@Saytan ?
@Jonny ///M ?
