Got my son a rift zone jr and it has that weird and funky QR rear axle thing. Has anyone converted to a bolt in axle ? Looking at parts available on the Marin site, I don’t see a definite solution. I guess it’s a 135 dropout now , but can be swapped to 142 , long story short, I don’t like it and am also building 26 inch wheels for him.
I haven't done exactly that swap, but I've done something similar: to upgrade my wife's Rift Zone 1 from the weird proprietary axle to a proper thru axle, I removed the adapter things from the frame and installed a Salsa Deadbolt Ultralight thru axle, part # FS0011, which is 12mm Axle Diameter, 174mm Length, 1.5 Thread Pitch, and 20mm Thread Length.
The (adult) Rift Zone takes a 148 x 12 hub when you remove the adapters.
Extrapolating, if the Rift Zone Jr. takes a 142 x 12 hub without the adapters, you would expect it to take a 168 mm overall length thru axle. The closest Salsa thru axle I can see is part # FS0010, 12mm Axle Diameter, 167mm Length, 1.5 Thread Pitch, 20mm Thread Length. That's 1 mm shorter than I would expect but it'll probably fit just fine. Matter of fact, her bike actually has about 1 mm of thru axle sticking out of the side of the frame, so 1 mm less would have been perfect.
Doesn't have to be a Salsa part either; I just ordered that because the shop where I work has a QBP account so it was convenient.
And yeah, when I got in touch with Marin themselves, they were no help at all.