Norton wheel bearing NM.17721, aka 4203 (2003)

Anonymous

Guest
Anyone have a substitution for the deep-groove double-row wheel bearings (1 fore, 1 aft) NM.17721, aka 4203 in a double-sealed version? I understand there may be a substitution that is 1.5mm wider. Thanks!
 
Joined
Sep 30, 2003
Messages
4
Re: wheel bearing

Thanks DynoDave! Yeah, I'd run across the Old Britt's page and that's helpful, and for now I've decided to take your approach; I bought new single-row sealed bearings from a local bearing supplier as they're not expensive, if my double-rows test out OK I'll repack and go w/ 'em, otherwise I'll go to the sealed ones, Old Britt's prices aren't too bad and I've got the equipment to do the mod.

dynodave said:
This link show the mod for putting in the wider sealed double row bearing....
http://www.oldbritts.com/wheel_upgrade.html

I haven't yet felt the need to try it. Grease the stock bearing every time you change the tire and you should be fine.
 

Anonymous

Guest
Re: bill

OK, thanks Bill! Both the 5203 and 5203-2RS are 17x40x17.5 vs. the 4203's 17x40x16, thus being 1.5mm wider than the standard bearing. So, the mod would have to be performed to "both ends" to get 'em to work, but w/ the 5203-2RS you'd have a sealed bearing.

bill said:
try a 5203 at your frindly bearing house

bill
 

Time Warp

.......back to the 70's.
VIP MEMBER
Joined
Dec 3, 2012
Messages
3,593
Anyone have a substitution for the deep-groove double-row wheel bearings (1 fore, 1 aft) NM.17721, aka 4203 in a double-sealed version? I understand there may be a substitution that is 1.5mm wider. Thanks!

5203, I machined 0.055" off the spacer (removed material from both sides)
Now a 2RS bearing is available off the shelf, any time, any where but at a hunch being 60 this year it won't be me fitting the next set of bearings. :D

Norton wheel bearing NM.17721, aka 4203 (2003)
 

Time Warp

.......back to the 70's.
VIP MEMBER
Joined
Dec 3, 2012
Messages
3,593
I machined a couple of alloy spacers to pull the bearings in with a long bolt.

The hub was warmed in the oven.
The threaded collar side pulled in until seated followed by the offside.

I measured around the same as the OldBritts website at 0.056" difference at the spacer top and bearing shoulder in the hub but elected to take 0.055'" off the spacer tube.
When the double row bearing is pulled in with that alloy spacer it is contacting the inner and outer race of the bearing and will stop when it is in full contact with the hub spacer even if there was a 0.001" air gap under the outer race.
I personally think that is the safer option and of course the stock 4203 bearing comes no where near seated in the hub.
I double checked by fitting the front axle and a spacer, torqued to check the bearing rotated smoothly.
It is possible to fit wheel bearings (not taking into account possible hub expansion with braking heat :D ) and they go from smooth running to notchy when the axle torque loads the inner races and the outer is retained in the hub bore.

Perhaps there is some merit in running C3's for the extra 0.0005" clearance for that same reason.

Norton wheel bearing NM.17721, aka 4203 (2003)
 

Ron L

VIP MEMBER
Joined
Feb 27, 2004
Messages
3,111
Country flag
Re: bill

OK, thanks Bill! Both the 5203 and 5203-2RS are 17x40x17.5 vs. the 4203's 17x40x16, thus being 1.5mm wider than the standard bearing. So, the mod would have to be performed to "both ends" to get 'em to work, but w/ the 5203-2RS you'd have a sealed bearing.
There is a European made 4203-2RS that is 17X40X16 available. Walridge Motors (Canada) has them for $54.40 CD$.
 

madass140

VIP MEMBER
Joined
Nov 6, 2011
Messages
2,121
Country flag
why modify your hub when the standard 4203 is readily available? doesnt make much sense to me
 

Time Warp

.......back to the 70's.
VIP MEMBER
Joined
Dec 3, 2012
Messages
3,593
The hub is not modified in any way Don.
The hub is over bored depth wise from the factory with a long inner spacer, some measurements and 2 minutes on the lathe reducing the spacer width and done.

It is almost like it was mean't for a 5203 bearing, no comment on one 4203 for $54.

It is nothing new and the OldBritts article goes back to 2002.

https://www.oldbritts.com/wheel_upgrade.html
 
Last edited:
Top