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154 Posts
Discussion Starter #1
Hi all, it's been a while since I've been on here I'm still racking up the miles, and continuing to evolve my 955i tona.

This time round it's the suspension linkages; I took them apart to check them out and the rollers disassembled themselves all over the garage floor. They were dry as a bone, apparently lubricated only with dust, the counterfaces were also corroded and fit only for scrap. I still need to pull apart the linkage axle on the swingarm but I'm not expecting it to be much better. Interestingly, the linkage axle on frame is fine; I replaced all these components about 20k miles ago and fitted grease nipples so I've been able blindly pump grease in once a year.

The correct replacement bearings would be HN2020, full complement, drawn cup needle rollers but, hell, these are expensive and I'm likely to need 4 of the things. Standard needle rollers won't do it; because the bearing are essentially fixed, they are loaded on only a small arc of their perimeter so as many rollers as possible are needed to be crammed into the space to share the load over.


Plain bearings: ideal for high load, low speed applications. Maintenance free, particularly using ptfe solid lubricant.
(I have some experience here; I design industrial bearing systems).

I'd like to be using INA bearings; EGB2020-E40 look ideal but the minimum order quantity is 100. Which, even at 70p each, blows the budget. GGB DU bearings are readily available however so that's what I'm going with. Unfortunately the O/D of the roller bearings, 26mm, is unusual. You could say it's an odd OD. 😁

There are two common problem with plain bearings: the first is that they can be susceptible to sticktion. This might be a big problem with suspension which requies a lot of very small oscillating movements. I wont know whether this is going to be a problem until I fit the bearings and they have worn in. Then it'll be obvious as chatter and harshness from the back end. The second, and it's one which DU bearings seem particularly susceptible to, is wear. Although the system will be sealed and bearings will bed in and should develop a good counterface; I'm concerned that they may not last long. This all depends on the loads which it's subject to; usefully all the loads here are directly related to the rear shock. Can anyone help me out with some detailed information here?

Am I right in thinking that the stock spring rate is 13.4kg/mm?
So, what's a typical load / typical travel at the shock? For that matter; what's the maximum travel?

I know the approximate static load; roughly speaking it'll be half the bike plus passengers (allowing a little more as the rear suspension will be taking all the pillion's weight)
Total static load: (200kg+75kg)/2 + 60kg ~ 200kg = 2000 N

What about in motion; what's the average shock movement, or what's the average shock load? Am I going to be a long way out assuming that the average dynamic loading is going to be half the static and that this will occur half the time?
Average dynamic load: 2000N * 0.5 *0.5 = 500N

There's a lot of assumptions there (and, as they say, I'm in danger of making ass out of... you know the rest) but the resulting bearing pressure is total average load distributed over the projected bearing area:
bearing pressure: 2500/(20*20) = 6.25 N/mm^2

This is absolutely tiny! GGB suggest that the bearing will last in excess of 10^8 cycles. (assuming that there's one 'bump' every meter; that's 60k miles.)

So: now I need to get some sleeves machined to take the housing from 26mm to 23mm (plus or minus a gnat's pube) then put it all together and see how it works. If this is a good solution then, if anyone is interested, I can put a kit together of all the bits so the problematic rollers can be eliminated from the linkages.

Additional bearing geekery......
The roller bearings seem to be specified on their stated fatigue limit. If the shock has 50mm travel then the peak load is 670kg, 6700N. A standard needle roller has a fatigue limit of 5400N but a full complement has a fatigue limit of, coincidentally, 6700N.
Theoretically, the standard roller's shouldnt ever wear out. To be fair; my bearings were working fine, despite the failure of the seals allowing them to gradually grind themselves to rust.

154 Posts
Discussion Starter #2
So, all of the roller bearings in the H section linkage are knackered so all will be replaced with plain bearings. The long sleeve is also marked but, as Triumph want £50 for it, I'll get a new one machined up.

The housings will need to be sleeved for the new bearings; down from 26 to 23mm. More machining.

Wish me luck; firstly in getting everything pressed together and then, the moment of truth; seeing whether everything moved freely and without squeaks...
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