How can you use a 13 or a 14 T pinion on the same WCP SS Gearbox?

It seems that changing the pinion size would require changing the position of the driven gear, or they would not mesh properly. How does this work?
I tried contacting WCP by phone and email but can’t reach them.
We were planning to buy couple of gear options to experiment with. Are we missing something that will prevent us from doing this?

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Iirc, once you get smaller tooth counts on pinions, the center distances arent always what you would expect. If you look at the drawings or assembly guides for the gearbox, it should show you the mounting hole options. I believe, 13 and 14 are the further away holes on the snowman little mounts, and the 11 and 12 are the closer.

Where you mount the CIM motor is a double hole slot for one of the bolts used to hold the CIM in place. The inside is for 11T/12T and the outer is 13T/14T.

See my attached picture.

As a note since we used these for several years, be aware that during competition if you use the 11T/12T slot a hard hit can cause the bolt to pop out to the 13T/14T position and cause major issues with driving. Take care!

So are the 13 and 14T pinions “close enough” to work. It just seems a little dodgy. It seems like the optimal distance is not the same for the pinions using the same snowman hole. Am I missing something?

Tooth profiles can be adjusted to give proper gear mesh with the “wrong” pitch diameter. See how the 11T and 12T CIM pinion tooth profiles compare. The comparison is similar for 13T and 14T, at a larger pitch diameter.


That is what we were missing. Thank you.

I would recommend using either 13 or 14 tooth pinions with these gearboxes. We used them last season with 11 tooth pinions and had all sorts of problems with them binding and/or the cim slipping into the outer mounting bolt hole. This year we used the 14 tooth pinions, which forced the cim mounting bolt into the outer part of the double hole and kept everything tight. This eliminated the slipping issue and we didn’t have any problems with them in either of this year’s competitions.


Definitely be aware that the 11/12T can wear out that slot and the motor can slip to the 13/14T side which will cause a lot of issues. We took hose clamps one year and strapped the motors together so that they were held to the 11/12T side. Not ideal, but works if you need to use that size.


I’ve seen this happen too and it’s a huge pain to fix when it happens. I’d be curious how many others have had issues with these sets of holes.

Can’t you just place a little piece of something to fill the gap in the slot that will be held in by the screw head? A little finicky I’m sure to get everything placed and aligned but should address any issues with slippage.

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Two different things going on here. Normally using a different tooth count gear will require a different C-C spacing. Hence the butterfly slot in some gear boxes. You can also engineer the tooth profile so a that different tooth count gears share the same C-C. If you look on the VEX web site for CIM pinions the ones with special spacing are noted. Using a regular 13 tooth pinion with 14 tooth spacing will turn out badly.

Vex/WCP 13T pinions are designed for use with a “standard” (20DP) 14T C-C spacing.

From their CAD download:

That’s a possible fix, but I could see that making servicing more difficult. The hose clamp was very quick to add/remove as needed.

Correct. Those are not standard 20Dp gears. Like the kind you would get out of the Martin catalog. I suspect the gears would work poorly if you tried to use the WCP 13T gear with the standard 13/xx C-C

This is a not uncommon trick in racing transmissions. It lets you slightly vary the ratios by changing one gear without changing the C-C distance.