Gearbox bearing clearances

I'm currently rebuilding the gearbox a 72 Commando 750 and have a questions regarding bearings I hope others can help with.

I have stripped the gearbox and removed all the bearings and given all the advise on this forum, I have decided to replace and have purchased the layshaft bearing on the drive side with a Hemmings type deep ball bearing with a fibre cage (6203TB ) which I believe has a C3 clearance as needed for gearbox and engine applications.

My question is related to the timing side main-shaft bearing removed from the inner timing side cover which is marked RLS5 but has no clearance marking, I'm assuming this bearing should have a C3 clearance ? When shopping online for this bearing from well known Norton suppliers and eBay, no mention is given of C3 clearance, so what's the deal, does this bearing need to be C3 clearance?

Steel bearing in alloy is normally C3 due to the interference fit, an older bearing pre ISO would have different markings, etched 3 circles, 3 dots are 2 possibilities. So have another look, I will check mine tomorrow.

Thanks Kommando, I checked the bearing I removed from the inner timing side gearbox cover and its marked RLS5'S, ITALY, C, K, SKF. I assume the C means standard clearance, I cannot see any other markings.

Looking at the other gearbox bearings I removed, the drive side layshaft bearing is marked 6203 2RS1, ITALY, C **, the rubber seals are missing but not needed and the clearance appears to be normal (C**). The sleeve gear has no markings at all but has a nylon cage.

I have already ordered a new Hemmings type layshaft bearing and a new premium quality sleeve gear bearing with C3 clearance. My only issue is with the timing side layshaft bearing where there seems to be minimal info as to the spec although I suspect C3 should be used.

http://www.nocnsw.org.au/technical/commando-bearings A very helpful link. I used it when replacing every bearing on my 74 Roadster. I was able to purchase bearings from where ever I wanted, as well as go with whatever manufacturer I chose. I was happy I found this info, as I had purchased bearings from a well known Norton parts supplier, that were made in China. After scouring the internet with the proper information at hand, I was able to purchase quality bearings from E bay, as well as a local bearing distributor. Hope this helps. Adios

The installed bearing has the markings hidden on the inside, I do have 2 Hoffman originals, both are marked V3 which is a vibration standard not clearance so they look to be CN.

Interesting that for the gearbox the list only mentions C3 clearance for the layshaft drive side bearing.

I guess this means I don't need C3 clearance for the sleeve gear and mainshaft timing side, which seems odd.

Would it be OK if I used C3 clearance for the three gearbox bearings or should I just use C3 on the layshaft bearing?

All info welcome

NORTSTER1974 said:

http://www.nocnsw.org.au/technical/commando-bearings A very helpful link. I used it when replacing every bearing on my 74 Roadster. I was able to purchase bearings from where ever I wanted, as well as go with whatever manufacturer I chose. I was happy I found this info, as I had purchased bearings from a well known Norton parts supplier, that were made in China. After scouring the internet with the proper information at hand, I was able to purchase quality bearings from E bay, as well as a local bearing distributor. Hope this helps. Adios

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The article is helpful. Thanks for posting.

I am rebuilding my '72s gearbox as well. That bearing on mine has England LJS/8C3 E BHP.