I have a 1970 built fast back and Ive just stripped the forks. The steering head bearings are the later type non adjustable but not sealed as they have a soft fiberous top washer that is soaked in lubricant. Maybe someone has done a conversion and sealed bearings seem preferable to me but when I check all the parts books for this type of bearing on later models 71on, they all have a tube spacer and mine does not. Do I need it?
If you plan to use the later…
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If you replace with the…
If you replace with the original cup and ball type bearing there's no need for the spacer, if you replace with the taper roller type you need the spacer to prevent excessive loading on the bearings.
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Steering Head bearing / spacer
Hi John and Alan, Thank you for your replies.
First of all I should say I am no engineer so I'm just applying some schoolboy maths to this subject. I have now done a little research based mainly on your initial comments and have found the following: Clearly I do need a spacer tube. The overall length of my headstock is 162 mm Inc bearings. In the current setup ( with no tube inner spacer) there are two non-adjustable non sealed for life ball race bearings with two inner race shims of 0.370" situated one at each end. Thus giving 0.720" step overall difference between the headstock length, including the flush bearings, to allow the yokes to 'Float' on the inner bearings. Taking the bearing dimensions for the 6025 2RS ( SKF) id 25mm, od 52mm, d 15mm, this would mean that the overall length of the tube required would be : 162mm minus the two bearing inner race depths at 15mm each. Thus 162mm minus 30mm Equals 132mm. John, the RGM tubes measure 134.5mm and129mm. Following your thoughts regarding allowing for an abatement gap for the outer bearings the fitting the 134.5 tube would make for a gap of 2.5mm split between both bearings. However I would have though it could be better practice to have both outer races fully home and use the shims to create the necessary extra inner bearing overall length ? As an aside I have discovered that Andover Norton do a bearing and tube spacer kit using sealed for life non adjustable bearings Part No 13.1768 for 68 -70 750 Commando but do not give dimensions so I have emailed their technical dept and asked for said information. Thanks again for your comments which are most helpful. Cheers Robin
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The bottom...
... race will be pushed home into the bottom housing by the weight of the bike. The load on the top bearing is almost (completely?) entirely radial so it doesn't matter if there's a space beneath the outer race and the housing. In my view it would be a mistake to try to get the "exact" length of spacer tube as it's likely to impose an end loading on the bearings.
I would fit the 134.5mm spacer tube.
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Whats the point of having a…
Whats the point of having a spacer with taper rollers ?.
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You would have thought the…
You would have thought the bottom race should be the bearing to be fully into the housing, I certainly did think that until I took one apart. If you look at the 6205 2RS setup the opposite is true. The headstock for this arrangement has the top housing at 15mm depth, just the right amount and no more, the bottom housing has a depth of 20mm allowing the bearing to float around by 5mm up or down, where it actually sits is determined by the length of the tube between the bearings but it never goes fully into the housing. I was told why this is the case once but its lost as I never wrote it down. In 40 years the top bearing on my 74 has never shown any movement, its still firmly in the headstock so I just accept the force from riding the bike never overrides the fit of the top bearing so it never moves, the tube adds the bottom bearing fit too so its two bearings that have to move.
Robin, try to measure the gap between the 2 inner lips that stop the bearings going in too far, the tube needs to be longer than this even if only 1mm longer. If it needs to be longer than 129mm then get the 134.5mm but be prepared to shorten it if one of the bearings sits proud of the headstock. The 6205 bearing will be 15mm dead on which saves you installing them to see where they will sit. If the AN one is 132mm then that would be perfect.
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I'm with Ian.
Ian is 100% correct. The bottom bearing takes ALL the axial weight, while top and bottom races share the radial loads equally. If it were the top one there would have to be a substantial retainer to stop the bearing being pushed out by a bump in the road!
As for Roberts taper rollers, these are normal ball bearings we are talking about here, not taper rollers Robert.
Regards, George.
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Yes I can see what you mean…
Yes I can see what you mean Ian, though to me the general idea of outer bearing races not fully in their housings still doesn't quite fit right in my mind. It would work for sure, but how about this scenario. Where I live there are plenty of pot holes and speed humps. If the suspension were ever to bottom out before recovering, would the top bearing, now having all the load in reverse, and the 'Shock' slide hammer effect not push the bottom bearing out and the top bearing in, to the extent of its available travel? If the inner race spacer tube is at a zero or factionally oversize fit with the outer races fully home in their housings then there should be no opportunity for any horizontal load on the inner race? My thoughts are that the whole design brief of a non adjustable roller bearing is for the outer race to be solidly fixed and the inner to revolve within it and any movement either radial or horizontal of the outer trace will damage the housing.
Happy to be told I'm wrong ~(;0)
It will be interesting to see what the dimensions of the Andover Norton Kit are, as it is a kit, I would assume they are a matched set..
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Just seen your further…
Just seen your further comments guys which opens it all up again. I guess the variables here are the type of bearing used size wise. Also clear now that a gap is ok or even desirable.
One thing no one has commented on are the two 0.37" shims that give the original ( incorrect ) set the clearance needed..?
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The dimensions of the…
The dimensions of the Andover Norton Kit are
Bearings 52 x 25x 15mm as expected and the tube 133.6mm which would seem to agree with all your comments.
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Hi George, I know we are…
Hi George, I know we are talking balls !! (we often are).. But Alan (third post) has stated that a spacer is needed for tapers, just interested where he got that ? and the reasoning. Thinking of fitting rollers to the under-steering Atlas.
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Just to finish, It turns out…
Just to finish, It turns out that whomever fitted the roller bearings used the shims from the previous adjustable ball and cap bearing and without a spacer. So I'm glad I took it down for a look.
Many thanks to all you knowledgeable guys who commented, now I have a plan for replacement.
Robin
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"though to me the general idea of outer bearing races not fully.
... in their housings still doesn't quite fit right in my mind"..... - wheel bearings are exactly the same - one outer is held in position by the screwed retainer, the other is free to find its own position. When you tighten everything down the bearing INNERS are held in the correct relative position.
TBH I've often wondered whether the bearing retainer is actually necessary as the shoulders stop the outers from going anywhere although I accept there could be some sideways motion and the bearing housings would probably wear. Not ready to test this out myself of course......
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There's quite a lot of…
There's quite a lot of earlier discussion on this back in the forum archives. One oddity relates to taper rollers. The Commando has coarser threads than the Dommie so taper rollers aren't as easy to fit. Also there are allegations that the ball bearing setup is not suitable for axial loads. But of course they are, provided such loads are within their rating. Which, apparently, they are.
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On the replacement fitment…
On the replacement fitment side of things:
Having now removed the existing bearings I find that both top and bottom abatements in the frame tube are 14mm depth. So both 15mm depth bearings when pressed fully home will protrude by 1mm at each end.
2 x 14mm from 161 = 133mm so the theoretical length of the spacer tube between the inner bearings with nil clearance is 133mm. The Andover Norton kit is supplied with 2 x sealed for life Ball Bearings and 1 x Spacer tube of 133.6 mm. That would appear to be the perfect size, preventing any horizontal load on the inner bearings..
Although I have been unable to get a conclusive answer on whether to use the two shim/washers, which sit one on the outside of each inner bearing, I shall try this as it gives slightly more clearance between the bottom yoke and the frame tube which is tight and should not affect the bearing set up.... probably..?
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There is...
... some discussion of the Commando setup in the NOC Commando Service Notes which may be helpful.
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If you plan to use the later 6205 2RS sealed ball bearings then yes you need a spacer, but not necessarily the later spacer but a special one as on RGM's site as your headstock is likely not the same as the later one.
Spacer to go from Featherbed to Commando bearings
https://www.rgmnorton.co.uk/buy/spacer-to-convert-dominator-to-commando-type-steering-head-bearing-067604_2226.htm
Later spacer
https://www.rgmnorton.co.uk/buy/steering-head-bearing-spacer-commando_2225.htm
The dimensions for both are on the links so you can check which would suit your headstock, the spacer should space the 2 bearings so one is not fully home in the recesses so that the spacer is holding the bearings apart.