Hi Greg many thanks for the comments please have a look at my last comment issue 18 regarding Paul richardsonMust be more to this...........The height of the pins in relation to the cam plate would still not cause it to jump into gear unless the pin was not engaged at all. Are you sure the two selector forks are the right way around, the blade one meshed with the double gear on the mainshaft at the rear and the slotted one sitting over both 1st and 2nd sliding gears on the forward lay shaft. Something in the gears themselves must not be engaged with the selector forks to cause this problem.