Hi all,new here,
I am building a 1955 engine to throw into my swing arm frame, I am confused about drive side roller bearing, the crank case has strengthening webs on drive side and roller bearing looks bigger than timing side bearing,I only have the outer race for drive side which reads Hoffman R325L also TH3 opposite to this, the measurment is 25x62x17mm,
I am looking for correct number for this roller bearing any help would be appreciated,thanks.
Normally MRJA 7/8 with a C3 spec.
B31 and early B32GS are the same.
In '54 the CB32 had a stepped crank pin with larger diameter next to the flywheel to be same as the 500GS
MRJA 7/8 spec:
Inside Diameter: 22.23mm = 0.875 (7/8) inch
Outside Diameter: 57.15mm = 2.25 (2-1/4) inch
Width: 17.46mm = 0.687 (11/16) inch
Seals / Shields: None
Clearance: C3
The later 350GS and the 500GS used the larger MRJA 1 1/8
It sounds like that is what was in your case, as it is the equivalent of the R325L so you may have a GS crank?
Does your drive side case have a bearing retaining plate on the inner aspect of the case retained by four hex screws and locking plates?
BSA service sheet 703 is useful for identifying bearings. The first image gives the BSA part numbers and the second page gives the standard bearing numbers for the BSA part numbers.
The R325L bearing is metric, the other 2 B31 bearings are imperial.. An internet search should help with suppliers and dimensions.
Thanks for info, my crank case does not have a plate on inner,engine number is BB31.11556 so not GS,
I am new to bsa b31s although been into motorcycles for many years,hence the need for information about this machine.
Thanks again for all info on this subject.
Julian is correct that drive side roller on B31 and B33 is metric with 25mm id, 17mm wide and 62mm od. But still c3 spec. The ts is the MRJ 7/8 with lip (same as GS). I've checked my spares box and only have the GS size for all three mains, all imperial!!
The DS is unlippe, TS has outer lip. I've used a single sealed ball bearing to minimise leakage into chaincase to suit belt primary drive option (there is a steel shim too).
I have ordered the T/S roller bearing which is a hepolite MRJA 7/8 C3,
the D/S roller bearing seems to be 24-724, 25x17x62 looking at bearing chart and as suggested by you guys, does it have to be C3 same as T/S,
I'm also having difficulty in taking out the clip holding outer ball bearing I've had it half out but can't quite get it to pull out any further, I don't want to damage casing,any hint on this?
I have checked this bearing on crankshaft for play and seems to be OK would you advise to renew this to ? Seems a no brainer while renewing other bearings,
Thanks
Quote from: Steve 80 on 10 Feb, 2026, 23:19 I have ordered the T/S roller bearing which is a hepolite MRJA 7/8 C3,
the D/S roller bearing seems to be 24-724, 25x17x62 looking at bearing chart and as suggested by you guys, does it have to be C3 same as T/S,
I'm also having difficulty in taking out the clip holding outer ball bearing I've had it half out but can't quite get it to pull out any further, I don't want to damage casing,any hint on this?
I have checked this bearing on crankshaft for play and seems to be OK would you advise to renew this to ? Seems a no brainer while renewing other bearings,
Thanks
I would replace the outer ball bearing as well. This locates the crank in the cases when the cush drive is fully pulled in and locked. I bought a Timken sealed version from Henderson Bearings (very helpful) I've removed the inner seal but left the outer to stop oil exiting into the chaincase. There is a thin shim that goes between bearing and case which stops flooding but I am after oil tight (NEB belt and dry clutch on this one). The circlip is a pain, flat blade first and then pliers and second flat blade to prise it out. Secret I was told is to use a modern clip with two holes for circlip pliers. Can't remember if it is same size as the hearbox circlip or rear wheel inner circlip off top of my head but the partlist should tell you.
If you have one of those little cheap screwdrivers that seem to collect in draws heat the end 1/8" and bend it to a right angle. This makes a really handy tool for getting behind these and o rings too.
Thanks Neil & Limeyrod for very useful advice, no doubt I will come across more problems in near future and will be asking for advice on certain topics from you knowledgeable guys.