TOPIC: Bearing Sizes / Undersize Mercury bearings?

I am rebuilding a Merc 500 Serial number 1599010. Having purchased bearings from two reliable sources I'm still having problems. I have put a micrometer across the new bearings and they are definitely imperial, although not genuine Mecury parts. However they will not fit properly. I fitted one of the needle roller bearings to the reverse gear but it was tight going in and once in I could not fit the shaft. Having measured the original bearings they are between 003" and 005" undersize. Is this common practice by Mercury to prevent anyone fitting non genuine parts?

they are precision ground bearings. military specs. and yes a few thousands smaller. you have 2 choices get your bearing with GB prefix or machine the gear out a few thousands.

Hi Dave

Many thanks for the info. I decided to get GB bearings rather than try and hold the gears in the lathe. I presume this only applies to the needle roller bearings (including drive shaft) and not to the ball or taper roller bearings.

I think only needle bearing and not all of them. check on the bearing for ####'s.