Clutch release bearing K series

[Ozzy]

Could somebody explain this for me please. I have recently had the CRB replaced under warranty. Caterham have admitted there is a problem with the CRB, but won't say what. Also, no sign of a remedy from them. What concerns me, is that this may fail again after a short time, outside of warranty. I have just read an interesting article in low flying by John Vine concerning preload tension. What is preload tension? If I understand this correctly, he's fitted extra springs to push the bearing carrier against the clutch plate fingers, in which case the bearing is constantly rotating. Having spoken to several other people, they are adamant that the bearing should sit about 5mm back from the fingers when the clutch is not depressed, ie not rotating when not in use. However, reading the article suggests that these extra springs apply downward pressure on the pedal, which would push the bearing forwards into contact with the fingers. Any thoughts would be appreciated, as this could be an expensive problem a few weeks outside warranty.

 

Still Shaking

[shn7]

Ozzy,

 

I think it's simply a case of conflicting views and who to believe. From what I know/have heard some CRB's fail after a few k miles and others go on seemingly indefinitely. I err towards the view that it should be in contant contact with the clutch cover springs and therefore rotating all the time the engine's running. Part of what sways me to this is that on so many sevens with the clutch pedal up there's a continual clatter from the CRB. As soon as some pressure (pre-load or foot) the noise abates and all is quiet (well relatively speaking).

 

Now in a tin top I've never heard this CRB clatter so can only draw the conclusion that in these installations there is some pre-load buit in.

 

So there's my 2d worth. I'm sure others will agree and dis-agree.

 

Steve.

[Colin Mill]

Hi Ozzy

 

I had a really good look at the CRB while I was putting the car together as I'd seen a thread here about the pre-load. All my previous experience had been with cars where the CRB comes clear of the release fingers so I was very sceptical about the whole thing. However this CRB is carried on a self-centring mechanism and I think this changes things somewhat. It seems as if the self-centring mechanism is not built to repeatedly self centre but to centre once and stay put for the life of the bearing (about 500miles 8-))

 

The argument seems to be that if you keep engaging and disengaging the bearing from the fingers the self-centering carrier will wear out and the bearing will just wobble about. So we seem to be stuck with keeping the bearing in contact with the fingers. With too little pre-load the fingers can skate over the bearing face and the thing cooks (the bearing carrier is plastic with a modest melting point of about 190c)

 

I reckon that with the current design of bearing we do unfortunately need a pre-load and one big enough to make sure the bearing turns with the clutch. I have done a mod. much as described by John Vine however I have done it using just one spring pulled out rather more (lower spring rate over more distance gives the same force but less change in tension as the clutch wears and the pedal moves). I checked the cable tension with a spring balance and its spot on 4kgf which gets you right in the middle of John's suggested range.

 

I'm still not too happy as its all too easy to pull the pedal up as you bring your foot up from below. This is going to take off all the pre-load for a moment and, if the original argument is right, will cause the self-centering carrier to 'work' as it re-seats. Given another chance at it I think I would fit a pre-poad spring at the bell housing end of the cable and arrange for a lost motion at the pedal end so that lifting the pedal would not unload the bearing.

 

 

[Ozzy]

Hi Guys,

 

Thanks for the replies. I think I understand what you mean, but surely constant contact with the fingers means the bearing is always rotating, and therefore, you would think this would considerably shorten it's life. Colin, could you reiterate what you think the life expectancy should be, this isn't too clear on your message.

 

Still Shaking

[Colin Mill]

Hi Ozzy

 

I agree that the constant contact looks like a bad idea from a life viewpoint. Personally I would rather a bearing that only engaged when you pressed the clutch. I even contemplated gluing up the self centreing carrier and setting it up with a retraction spring in the bell housing but since its new and covered by Caterham I thought I'd go with what they wanted. If the bearing is designed right I guess it should do the time. An alternator front bearing is running quite a bit faster with a fairly heavy side load and they generally cope fine for years.

 

Sorry I was trying to make a joke of the bearing life - I think I read of one doing only 500 miles before dying so perhaps its not a joke.

 

I can't believe they can't get this right - a CRB is not exactly an automotive novelty item and my tin top has done near on 120K on the original clutch and CRB.

 

[Bricol]

bearings are a lot happier spinning al the time rather than suddenly having to spin up from zero to 6 / 7000 rpm in no time at all - the inertia of the internals cause it to skid against the clutch fingers, doing them no good at all, and the inner rave against the plastic holder - doing that no good at all. The internals probably skid as well - doing the races no good and not doing very much with the internal lubricant.

 

It is spins all the time, it's not doing either of the above - it'll get warm, but not from external sliding friction.

 

think of aircraft wheels on landing - no rotation to lots in no time under considerable loading - the smoke is the tyre skidding - and wearing . . .

 

I reckon if you've used a relatively modern car (last 10 yrs) most will have had a constantly engaged CRB - if you look at the top of the clutch pedal you will see a plastic spring loaded quadrant on the top - contantly tensions the cable and takes up wear every time you depress the clutch pedal - my 1984 Renault had one.

 

Older cars had more robust bearing, more robust clutches and metal, robust (think I've used robust enough times now) CRB carriers with the inners locked to it better - so skidding didn't have so much effect.

 

My CRB in my K is now grumbling a lot - not all the time - pumping the pedal shuts it up most of the time - I wil certainly be looking to add pre-load on replacement - but I will be trying to add it at the clutch end - stop loading the cable and to take account of cable stretch.

 

Bri

[Big Brother]

Why does this mainly seem to affect K series cars?

Caterham have been using the same bearing since around 1985 (ish) with no reported problems

Is there anything specific with the installation on the K series?

 

 

Steve

Se7en-Up!

 

It'S NOT Green!

[Colin Mill]

I heard this thing about the bearing not liking spinning up fast but if it were a frequently encountered problem you would expect it to appear in bearing specs. I've never seen a max dOmega/dt quoted in any bearing catalogue and I chatted to one of our bearing factors who has never seen anything about it either. The whole bearing only weighs 167g and the speed of the bearing face at 6000rpm is about 30m/s which is not that fast. The info I got from CC also makes me question this. When I spoke to the factory about this problem the person I spoke to told me that they used to run this bearing without any preload and that they changed to using a preload on advice from the bearing manufacturer. Apparently both the non-preloaded scheme and the later pre-loaded scheme gave no problems. So the problems don't coincide with a change in the way the bearing is being used. I wonder if it has something to do with a materials change from which the self-centering carrier is made - it does not inspire much confidence especially when you see how easy it is to soften the stuff with a soldering iron.

[Mick Day]

Steve

 

Part of what sways me to this is that on so many sevens with the clutch pedal up there's a continual clatter from the CRB. As soon as some pressure (pre-load or foot) the noise abates and all is quiet (well relatively speaking).

 

Now in a tin top I've never heard this CRB clatter so can only draw the conclusion that in these installations there is some pre-load buit in.

---

.

The noise you can hear is the input shaft in the gearbox rattling. Depressing the clutch stops it rotating so the noise stops. The reason you don't hear it in the tin-top is better insulation & gearbox design.

 

Mick

 

Edited by - Mick Day on 1 Oct 2004 23:28:12

[shn7]

Mick,

 

Happy to be corrected Come to think of it (and we're going back a few years) I had this on an Alfasud so maybe not all tin tops had enough insulation 😬

 

Steve.

[V7 SLR]

Didn't think much of the preload theory until I noted that my perfect condition 25K mile CRB benefits from a spring on the clutch pedal. Now I'm totally convinced. Also 2 engineering friends I've spoken to about it are equally convinced.

[Nov-07]

A well-known car maker, located in D******d, told me "we have just been informed by the manufacturer(of the CRBs) that they should be pre-loaded", i.e. continually spinning. This topic has really been done to death in other threads. Pre-load your CRB and be happy 😬

[Jason Plato]

If you do a search for this topic , you will finds loads of info .

 

In short , the bearing as fitted on a k series caterham has little or no preload , the manufacturer has been contacted by a few members , and the same bearing is widly used on 10's of thousands of other "normal" cars with a set preload and auto adjustment for clutch wear . When used in this state the bearing goes on for many 10's of thousands of miles ......

 

My guess is that some cars have slightly more preload than others - by chance , and these are OK . Others have none and these wear very quickley .

 

I suspect that there may also be other influences aside from he main preload issue ? , maybe the driver rests his foot on the clutch pedal ?, the position of the pedals may affect preload ? , the manner in which the clutch is depressed / released ? . But I have no evidence to make any link .

 

Caterham have now said they are looking at a solution .

 

 

 

 

 

 

C7 TOPhere

[John Vine]

A well-known car maker, located in D******d, told me "we have just been informed by the manufacturer(of the CRBs) that they should be pre-loaded", i.e. continually spinning.

That's encouraging. But do you happen to know whether they are now applying the pre-load at build time (or, indeed, on aftersales repairs)? And if they are, do you know what mechanism they are using, and how much pre-load they are applying?

 

I err towards the view that it should be in contant contact with the clutch cover springs and therefore rotating all the time the engine's running

And you'd be right! That's precisely what should happen, according to INA (the CRB manufacturer). A suitable pre-load ensures that this happens. INA recommend a pre-load of 80-120N, which is what my extra springs achieve (by increasing the cable tension).

 

JV

 

Edited by - John Vine on 4 Oct 2004 18:42:29