Main Shaft High Gear Bearing

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Main Shaft High Gear Bearing

Postby Martin.S » Sun Nov 18, 2018 2:08 pm

What is so special about this bearing - NU205 M.FAFNIR?

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Re: Main Shaft High Gear Bearing

Postby Mick D » Sun Nov 18, 2018 2:36 pm

Hi

See here for specification - alternatives may be available:

https://www.ahrinternational.com/FAG_nomenclature.shtml

Regards Mick

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Re: Main Shaft High Gear Bearing

Postby Ozmadman » Sun Nov 18, 2018 2:38 pm

Martin.S wrote:What is so special about this bearing - NU205 M.FAFNIR?

Its a special size and runs directly on the gearbox output shaft with no inner race. If you try to use a normal RU205 bearing without the inner race provided with it is 1mm too large across the rollers and will not fit (I have one so I know!!) They are expensive and you can either buy one from club spares which be be identical to the original one or one from simply bearings (Like I did) which is a slightly different design but similar price. There is no way around it, if you need one you will have to cough up about £80 as far as I remember. here is a picture of both types
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Main Shaft High Gear Bearing

Postby Mick D » Sun Nov 18, 2018 3:08 pm

Hi Paul

I always understood bearing identification was a fixed standard and as such all NU205 bearings would conform to identical dimensions, in this case the diameter to the inside of the rollers being 31.5mm, is this the diameter of the gearbox shaft?

Out of interest, are you able to tell me the make and number of the bearing with the smaller dimension?

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Re: Main Shaft High Gear Bearing

Postby Ozmadman » Sun Nov 18, 2018 5:45 pm

I will have a look later when I can fish it out. This bearing is RNU maybe the R is relevant?
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Main Shaft High Gear Bearing

Postby Mick D » Sun Nov 18, 2018 5:51 pm

Hi Paul

'R' is the designator for a bearing supplied without an inner race.

The 'M' on the original indicates a machined cage, (brass), as opposed to the pressed metal one in your replacement.

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Re: Main Shaft High Gear Bearing

Postby Martin.S » Sun Nov 18, 2018 7:17 pm

This is looking good, My High gear is in good nick apart from the bearing track, this track measures 31.95mm diameter.
Looking at the SKF site - a NU205 ECML has a inner bearing piece and this has an outer diameter of 31.5mm, so I'm thinking I could grind 0.45mm off the high gear and use this bearing without its centre. Grinding 0.225 ( 9thou) of the radius might remove the case hardening, I wonder how much to have it Nitrided?
Lambretta's appear to use these bearings and are only around the £20 mark.

IMG_20181118_134552.jpg
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Re: Main Shaft High Gear Bearing

Postby Mick D » Sun Nov 18, 2018 8:04 pm

Hi

I'd pay the money for the real thing rather than faff around with the gearbox - it'll be cheaper in the long run.

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Re: Main Shaft High Gear Bearing

Postby Ozmadman » Sun Nov 18, 2018 8:11 pm

Mick D wrote:Hi

I'd pay the money for the real thing rather than faff around with the gearbox - it'll be cheaper in the long run.

Regards Mick

But he needs a good output shaft which may only be found in a s/h box??
Paul
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1974 Yamaha RD250B US Model 6 speed

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Re: Main Shaft High Gear Bearing

Postby clanger9 » Mon Nov 19, 2018 12:52 am

If you can find a solution for output gears with a knackered bearing track then Lightweight owners will be very grateful! Decent output gears are getting hard to find...
1966 AJS Model 14 250 CSR "cafe racer"
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