I had good experiences with Robinson pininions for my Summit,the catch is that the Summit although an 1/8th scale very similar to the Nero running the same brushless motor I have in my Nero now and a 5mm shaft and all.....ran MOD .08 and not MOD 1 like the Nero. I would almost guarantee you got a hold of a pinion that is "almost" the right pitch but just off enough to not mesh well. I have run Castle and Robinson MOD 1s and they mesh fine on the Nero.