Oberon Clutch slave leaking

[Capo]

Have a look at this, the pushrod etc. is a different colour also notice it is surrounded by a thick black line as is the feed on the crank pin journal.
The only way for oil to get in there is if there is a hole in the shaft.

[Dukedesmo]

But does not the shaft end, exposed inside the casting with the oil hole above it (as per the pic), whilst the 2 'O' rings are in the thick portion of casting on the outside of this hole?

Meaning that inside the hole the pushrod is exposed at the end of the shaft and the oil pools around the rod whilst the shaft rotates and the rod moves in and out when operated.

Also the shaft is narrowed along much of it's length (ends are obviously a good fit in the casting at the slave end and the bearings at the clutch end) so that there is a good gap between rod and shaft and so the rotation of the shaft, therefore the small pool of oil serves as a 'feed' to run into the shaft, up to the oil seal at the clutch end and so supplying the inner bearing with oil?

[Capo]

Originally Posted by Dukedesmo

But does not the shaft end, exposed inside the casting with the oil hole above it (as per the pic), whilst the 2 'O' rings are in the thick portion of casting on the outside of this hole?

Meaning that inside the hole the pushrod is exposed at the end of the shaft and the oil pools around the rod whilst the shaft rotates and the rod moves in and out when operated.

Also the shaft is narrowed along much of it's length (ends are obviously a good fit in the casting at the slave end and the bearings at the clutch end) so that there is a good gap between rod and shaft and so the rotation of the shaft, therefore the small pool of oil serves as a 'feed' to run into the shaft, up to the oil seal at the clutch end and so supplying the inner bearing with oil?

I think your right, the O rings seal in the case not the bore of the not bore of the shaft as I had thought. There is also a radial hole in the shaft on the clutch end to allow the oil to escape, possibly the centrifugal force of oil escaping from this hole, induces flow from the other end.

[utopia]

Well, that was interesting, and quite fruitful too.
I'm glad I asked.

From the beginning of my discussions with Capo, I had been convinced that there must be a oil supply to the little needle bearing in the clutch end of the shaft bore.
Furthermore, because of the position of the adjacent seal, the oil supply had to be along the shaft from the slave end.
I was also convinced that there had to be both an oil feed and also a bleed/drain hole of some sort.
....but I could see neither.

The penny began to drop when Tim outlined the feed path through the slave end bearing, pointing out that the pushrod o-rings seal on the casing, not the bore of the shaft.
So that was "in" but there had to also be an "out".
I scanned ebay pics of secondhand shafts but could spot nothing there.
Imagine my pleasure when I then noticed the little radial hole clearly visible on the cross section drawing that Capo posted.

To complete the circle, there is also the issue of where the oil goes after it exits the little hole.
This hole looks perilously close to the clutch basket splines.
Hence it is close to being masked by the nearby bearing.
In any case it is too far outboard to exit inboard of that bearing ..indeed an exit path into the clutch case looks more likely .. not good on a dry clutch motor.
So I reckon this hole must line up with a short void between the bearing and its (outboard) seal, and then the oil exits this void through the bearing and into the inner crankcase.

I'm not entirely convinced that centrifugal force is the sole or main driving force for the flow .. though it probably contributes.
So too, but more so I would think, would the static head from the little oil gallery above the bearing at the inlet end.
I kinda suspect that there may also be some sort of surface clingy effect (Coanda ?) going on, and maybe some general creep when the rod moves in/out or spins a bit.
Its also worth considering that some flow from the oil gallery might take place while the bike is parked up.
But then again, the sidestand tilts the wrong way for the oil to go far before having to go uphill.

Anyhow, must say, this is one of the joys of a good forum.
Ta.

[Dukedesmo]

I've never noticed the radial exit hole in the clutch end of the shaft but I suppose there should be something or the oil in there would be as old as the bike and eventually get gummed up in the bearing, causing it to seize and defeating the objective.

I've also often wondered why the narrow section of the rod (inside the shaft) is in a 'rough' finish, obviously it doesn't run on anything so doesn't need to be machined smooth so I assumed it was purely a cost thing? but maybe the roughness also encourages the oil to stick to it better, allowing the feed to be more effective?

The 'O' rings sit in the case to stop oil leaking out onto the slave cylinder area (though you'd hardly know if a little leaked) but, presumably also stops chain oil/crud from potentially contaminating the oil?

If you think about if the 'O' rings were in the bore of the shaft then what would stop the pushrod from spinning with it due to the friction? and if it didn't then the 'O' rings would be worn away by the shaft constantly riding on them?

As it is the only contact between shaft and pushrod is through the little bearing which is precisely there to prevent rotation, although there will be a small amount of drag through both it and the accompanying oil seal.

Otherwise the primary drag is from the pressure plate through the bearing so as long as the bearings are good then the rod won't spin. If it does then the slave cylinder won't last long, which is what the Evo slave cylinder bearing was claimed to help in the event of the rod spinning - although I would think that at the point the shaft is spinning the slave's days (even with a bearing) are numbered.

I don't know how common the rod spinning is but Ducati saw fit to put an anti-spin pin/attachment on recent models, so it must happen sometimes? but I'm certain neither of mine spin - if they did then they'd be going at up to 5000 rpm (clutch runs at around half engine speed - depending on primary drive ratio) and I would imagine the slave would start to get very hot, very quickly and wouldn't last long?

For that reason it's worth changing the pressure plate bearing regularly - they're not expensive so good insurance. I've also changed the inner bearing in the shaft on both of mine even though neither was causing any problem, again they are cheap enough and easy to fit (also need the oil seal) but, be warned the old one can be an absolute sod to remove as you can't get a purchase behind it due to the shaft behind it being the same ID as the bearing. The one in my 916 came out fairly easily but on the Monster I had resort to die grinder/small chisel and then pick out the pieces, I soon started to regret starting the job.

Plus, if you do change it be sure to fit the oil seal with the 'lip' pointing inwards (I now use reading glasses when fitting small parts!) or it'll leak oil into the clutch. That said I don't know if wet clutch bikes have the seal as it would be OK, indeed probably preferable to let the oil pass through the clutch?

The oil seal is also the reason that the pushrod should, ideally be removed from the slave end as pulling the 'O' rings through the seal could damage it, so always best to remove the pressure plate from the rod first and then pull the rod out from the left side. It might need some 'persuasion' to separate though and be careful that if you run the engine with no clutch (enjoy the silence on a dry clutch bike!) that unless the rod's in place oil will come out of the shaft.

[Capo]

If the static head was 25mm, this equates to 0.0361 psi or 250 pascals for water, for oil it would be less.
This would hardly be enough to drive a viscous liquid along 10 inches of shaft through relatively small clearances
I have seen first hand where with a static head of 4 feet, the friction of the connecting pipework was great enough to prevent any flow what so ever.
The rod itself will act as a positive displacement pump each time the clutch lever is operated

[jerry]

My oberon Slave has no ANTI SPIN pin ,,

would putting a ceramic bearing in the clutch throw out improve anti spin ??????????

also went for a ride today and the NEW seals were visibly drip leaking after 20 miles so I went home ,,bugger relegated to 113cc scooter ...

going to bring both slaves with me to UK later this week ,,one will go to Oberon for new seals and a check up and the ducati one , i will get the tool needed to open it and see why a refurbed unit is leaking ,, i suspect it was not torqued up enough when reassembled ??

[utopia]

Originally Posted by Capo

If the static head was 25mm, this equates to 0.0361 psi or 250 pascals for water, for oil it would be less.
This would hardly be enough to drive a viscous liquid along 10 inches of shaft through relatively small clearances
I have seen first hand where with a static head of 4 feet, the friction of the connecting pipework was great enough to prevent any flow what so ever.
The rod itself will act as a positive displacement pump each time the clutch lever is operated

If I get a 10 inch length of small bore tube, fill it with oil and then prop one end up on a 25mm block, the oil will have no trouble at all running out of the low end of the tube.
I would say there's more than enough pressure.
After all, we're only after a dribble, not a flow as such.
Also, I wouldn't exactly call the pushrod a "positive" displacement pump .. at best it drags an indeterminate amount along the shaft each time it moves.. as I mentioned before.
But no matter how much oil either of these mechanisms shift, in my judgement they will both have significantly more effect than the centrifugal forces in the bleed hole.

[utopia]

Dukedesmo ..
1) I don't know exactly where the reduced dia is along the pushrod (didn't even know it was there as I've never had mine fully out) but maybe it acts to form a chamber to "grab" some oil and move it along the bore of the shaft and into the wider-bore section more efficiently than if it were just being dragged along on the pushrod's plain surface ? In which case the pumping might be a little more "positive displacement" than I suggested earlier.
2) I have been coming to the conclusion that, as you say, the pressure plate bearing is worth changing as a matter of course .. mine's been there for 25k miles. I don't think I'll bother with the internal needle roller though .. there's no load on it to speak of anyway.
3) I hadn't thought about it from the point of view of the seal but I was thinking that its probably best to remove the pushrod from the slave end also, because doing it the other way, in the event of the o-rings being damaged there is a chance, albeit a small one, that they might pop off the pushrod and become lodged in the wider bore of the shaft.

[Darren69]

This has been useful. Now I'm thinking that maybe my slave isn't leaking after all but the outer o-ring on the pushrod may have failed instead. Further investigation is necessary. Its difficult to tell if its hydraulic fluid or oil by the time it has dripped through the chain run. I will have to pull the slave off again and take a closer look.

[Dukedesmo]

Originally Posted by utopia

Dukedesmo ..
1) I don't know exactly where the reduced dia is along the pushrod (didn't even know it was there as I've never had mine fully out) but maybe it acts to form a chamber to "grab" some oil and move it along the bore of the shaft and into the wider-bore section more efficiently than if it were just being dragged along on the pushrod's plain surface ? In which case the pumping might be a little more "positive displacement" than I suggested earlier.
2) I have been coming to the conclusion that, as you say, the pressure plate bearing is worth changing as a matter of course .. mine's been there for 25k miles. I don't think I'll bother with the internal needle roller though .. there's no load on it to speak of anyway.
3) I hadn't thought about it from the point of view of the seal but I was thinking that its probably best to remove the pushrod from the slave end also, because doing it the other way, in the event of the o-rings being damaged there is a chance, albeit a small one, that they might pop off the pushrod and become lodged in the wider bore of the shaft.

Here's a picture of a pushrod, as you can see it has a reduced diameter for much of it's length. Being 8mm where it sits in the bearing/seal and the LH case but only 7mm in the centre portion.



Obviously done this way for a reason as it would surely be cheaper to leave it at 8mm for the full length. As above the 7mm section isn't polished, it doesn't need to be as it contacts nothing but I wonder if it also contributes to moving or holding the oil?

The 'O' rings are quite thick (as you can see by the grooves - I think 6mm ID?) so I doubt they'd come off inside the shaft? but they will pull at the oil seal so best not to pull the rod through.

I have heard of pushrods breaking (probably because the bearing failed?), usually at one of the 'O' ring grooves -they may still work but cause all sorts of havoc so worth pulling it out now and again to check?

The bearing (at least in the dry clutch) is the same as those on the belt pulleys, costs less than a fiver so worth changing occasionally, of course wet clutch bearings should have an easier life but less frequently seen so I would definitely change if the clutch was apart.

The needle roller in the shaft is, as you say not likely to wear but worth checking if you're in there and again they are cheap but tricky to remove.

[utopia]

Ta .. that clarifies things.
Clearly the reduced central portion is maximised along the length, perhaps suggesting that the aim was to maximise the volume of the oil-holding void and hence ensure a more reliable supply of oil to the needle bearing.
This further leads me to suspect that the hole in the shaft is merely an air bleed, its only purpose being to "allow" the oil to flow rather than to "cause" it to flow.
I say this because there is no point in exhausting the flow from the hollow shaft .. indeed the aim would probably be to retain as much oil in there as possible.
All somewhat conjecture though.

The rough finish on the central part of the pushrod will be there, as I'm sure you realise, because its the finish left from the turning operation, after which only the end seal and bearing surfaces would have been ground.
It may contribute to oil movement but if it does I would say that its probably a happy accident rather than an intended design ploy.


The only outstanding element in all this of which I am still a tad uncertain is the detail of the case/bearing/seal arrangement behind the clutch where the bleed hole in the shaft is.
If anyone has a pic of this I would be interested to confirm my reasoning that the bleed hole must exit between seal and bearing, thereby allowing the oil to flow back through the bearing and thence into the inner crankcase.

[Luddite]

Originally Posted by Mr Gazza

In order to simplify the question to Luke or Craig, does anyone know offhand what the length of the Oberon spacer piece is? From memory it's about 10/12mm long.

Found it! I couldn't see it for looking last night. The Oberon spacer for the CLU-116 is precisely 10mm long. This would make sense as I believe the pushrods went from 325mm to 335mm with the introduction of the new-style cylinders.

Hope that helps.

[Dukedesmo]

Originally Posted by utopia

It may contribute to oil movement but if it does I would say that its probably a happy accident rather than an intended design ploy.

Quite possibly and obviously it would be an unnecessary cost to grind it but oil should stick better than it would to a 'polished' surface. Indeed when I've removed mine there has been quite a coating of oil on it.

As for the bleed hole, I don't recall seeing one and if there is one it must be a fair way back from the bearing because there's quite a length of shaft inside the clutch with bearing being in the end, as per these pics;

[Capo]

Mines nice and polished