Fighting bro pinions

is there anything special about fighting bro pinions?

pitch? depth? diameter?

Some background

I built for a mate into a wells some FB 16:1 and he’s got one of those comfortable molded grips. He didn’t have a specific FB pinion for me.

Shimmed quite nicely, pretty standard bearings into a wells box. No shims under the bevel, it’s a s low as it goes. The bearings sit in, not tight, not loose…pretty normal.

First build I noticed that the motor height was about half contact with the bevel. I didn’t like it. It was far too tight, it went to the field and shagged the pinion… no surprise.

Take two…he gave me another pinion, seems to mesh ok but not perfectly and again, half contact…

Hours later I’ve swapped the grip for a stock grip, dropped in my old wells bevel and still the best I can get is a poofteenth more contact with the bevel, seems excessively stiff.

It’s a sticking point for this build…no decent pinion height == now pew pew and I just need this wretched thing off the bench

The first thing before shimming is to set the pinion in the right place on the motor shaft… easy on a Gen8 style where the motor cage is connected to the gearbox when it is out of the blaster… a Gen9 you have to screw the hand grip to the gearbox, then trial fit the motor and keep shifting the pinion until it meshes right with the 1st gear with the 1st gear shimmed properly. If you need to use any more than one of the thinnest shims on the first gear, you need to move the pinion closer to the motor on the shaft (or back the motor out) or you may run out of room to get the last gear (sector gear) in the right place.

You can work the other way too… shim the gearbox completely, then (Gen9) screw on the handle, insert the motor and adjust it to the correct position of the pinion to first gear… you may have to pull out the motor a few times to get the pinion in the right place on the motor shaft.

A whole lot of trial and error… but fun when it is done :+1::grin:

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Are your bushes flush with the gearbox surface ? If not then you can file them down to allow more clearance so you can get the correct pinion height.
Otherwise try a few different brand pinions and gear sets, they are not all the same.
Btw there is only one correct motor pinion height, the back of the pinion must be flush with the outer edge of the bevel gear.


Well I’m on the same page as you two and above echos my many many build actions to date…

@Calcifer wells m8, think V2 but shimming is second nature to be and usually no more than 30mins including a run in.

@Rattler, I had had that bushing flush thought also. The bearings he has sit a little lower than the stock wells bush.

I might put a filed down bush in that hole but I really dislike doing that sort of thing but I prefer that to grinding out the box

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Well you have no choice unfortunately.
I have had a few gen 8 style nylon boxes that were the same and it’s a pita.
There is also a possibility that you will have to file all three bushes down on that side, because you have moved the bevel it could rub on the the gears if you don’t move them all equally.

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well…pinion height done…and TFFT…

file fit, repeat and repeat and repeat…feels like i’m repeating myself here…

i took about 0.2mm of the bushing and just finished the lab psu fed find the sweet spot game…

0.2mm definitely means i have to reshim but i’m not terribly meh about that. i don’t really see shimming as any great problematic task which is why this motor height pickle only on this blaster has been shitting me to … well… murderous rampage…

now…being unable to use his bearings on one side of the box…i can see him really liking that but at this stage i’d rather not just so i don’t need to take down the other bushings.

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