Bootmachine, I ran exactly the same pinion combo ( black and blue gears ) and found that after three tanks, they had worn the teeth into knife edges that were so sharp, I cut my finger pretty good on them. I switched them out for the steel 'welded on' pinions from the rally set up and I have run them for gallons with no problem what so ever. I think the ali that is used in the pinion options is very soft and just wears away very quickly.