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help me fix the bearings in my freewheel. I need to know the number of ball bearings top and bottom in my shimano mf-hg20 freewheel, and what size are they?

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Take a ball to a bike shop and they will be able to tell you the size. Generally, with new balls, the race will be full with about 1/2 ball space left. With used (worn) balls the rule is a full race minus 1 ball. Never jam a race completely full -- there should be 1/2 ball space minimum. – Daniel R Hicks May 27 '13 at 18:30
(Though in a pinch you can run a bearing short 2-3 balls, though wear will be increased.) – Daniel R Hicks May 27 '13 at 18:31
Are you really replacing bearings in the freewheel itself, or in the hub to which the freewheel is attached? If it really is the freewheel says "You also will need about 100 1/8" bearing balls for most freewheels". But it also says don't bother unless you really have to. If, as I suspect, it's the hub, do you know the model number of that? – armb Jul 1 '13 at 8:48

According to

There are thirty-eight 3.0mm inner steel ball bearings used in the inner bearing assembly

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Pus "twenty-eight 3.0mm steel ball bearings used for the outer bearing assembly". So he needs 66 total. Plus a handful of spares, because the chances of putting 66 ball bearings in place without dropping a single one on the floor is small.... – armb Sep 3 '13 at 12:07
I'd need at least 20 spares. – Daniel R Hicks Oct 2 '13 at 11:58

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