Problem with BB gearbox spacer

When we attached our two BB gearboxes to CIM motors, one made a loud skreeching noise.

Upon examination it turned out that the black metal spacer that goes between the CIM motor and the pinion gear was ~ 1mm too long. A quick trip to the bench grinder fixed the problem, and the gearbox runs smoothly now.

What is the dim of the spacer now that you cut it down by 1mm?

Will anyone who has successfully run the CIMs with the BB 56mm trans please measure their spacers and post the dimension on this thread?

If we get some good data, we can perhaps have FIRST or BB send out an all points bulletin with the news to check your spacers for the right dimension.

Joe J.

Hi all,

The spacer I checked on one of the gearboxes did not have a 5/16" or 8mm keyed bore. Instead, it was much smaller, almost around the 1/4 or 9/32 range and would not fit on the shaft. I had to drill it to 5/16" and trim the key slightly to fit eveything in. I don’t have access to the internals of that one any more, as putting it together and not having the thing seize or grind terribly (was not a spacer issue - appeared to be small manufacturing flaws causing everything to align in only one orientation) was a two hour ordeal!

The QC on the gearboxes seems pretty interesting to say the least. I hope they hold up under use. :o