Rear hub difference RM250A/B/C

[micko]

Apart from bearing sizes is there a difference, are they all magnesium ?

[LWC82PE]

They are all aluminium as shipped on the bikes from factory. There were optional magnesium rear hubs for the 76 and for the 77/78

To convert the 76 hub to use 17mm axle use bearings  KOYO DG1742RSC3 - 17X42X13  (they are only available with a seal on one side)
To convert 77/78 hub to 15mm axle use bearings  SKF 361202 15x40x11 with a 2mm shim or machine out the hub to use the stock 76 bearings which are 6302   15X42X13

[micko]

Thanks for the info

[211]

some of the very first RM A series used the left over RH/RN parts bin and I have seen a few with the tel tail 400000 part number sand cast into the hub (inside)
keep your eyes out for that one