Clutch Failure - Sense Check

[John Vine]

And JV - "Whether that has any bearing on the issue..." ... Oh dear!

Yes, sorry about that!  It kinda fell off the keyboard when I wasn't looking.

JV

[revilla]

Further response from AP:

Hello Andrew,

 

A couple of comments.

• In the attached picture the contact area does not look concentric? It may only be the angle the picture was taken but the wear marks are not even across the high point on the finger. If this is correct it will load the clutch and cause the cover to fatigue.
• The clutch is not designed to run with a pre-load. This is a road car solution to bearing wear. Keeping the ball bearings running at all times reduces the wear as the ball bearings only skid during acceleration, this is the main cause of wear. The wear on the bearing face looks normal. There will not be much heat generating during normal clutch engagement.  

 

Regards,

 

Jeremy

I don't understand that response on multiple levels:

The "uneven wear" across the high points of the fingers, if it does exist and isn't just the angle of the photograph as I believe, doesn't make sense in terms of the clutch and gearbox being misaligned. The clutch rotates so even if it was misaligned I can't see why it wouldn't wear all parts of the clutch equally in turn? It would only make sense to me if the clutch cover wasn't concentric with the flywheel (very unlikely unless as it was correct bolted and dowelled) or the clutch cover was not itself symmetrical, surely?

As for the preload (which I mentioned in my email to him), he says it doesn't need it (thoughts, John?) but then his explanation of why sounds like it does need it! Or should I read it that the preload is a road car solution ... and this is why it used on road cars  ...  but this isn't a road car clutch, it's a competition clutch? I can see what he's saying, that the wear in the bearing occurs mostly during acceleration from a standstill to engine speed as the bearing engages the clutch and you get less wear if you keep the bearing running all the time (which is still surprising but kind of makes sense) but if so, why doesn't that apply in this case?

[revilla]

Actually, looking again at that picture I can kind of see what he means that some fingers look like they have taken more wear than others, but I can only see that as being an internal issue with the clutch (or quite possibly wear from when the clutch had already failed and was out of shape with all the cracking, as there was a large crack that was circumferential around one side of the clutch and was allowing that part of the cover to lift a little).

[Wrightpayne]

I smell a BS side step!

If the bearing has the correct pre-load does the bearing face always stay in the same place on the pressure plate fingers - I think not!

I think pictures always gives them an excuse. Face to face meeting with the components on the table may yield a better outcome - is it worth the effort ? Probably not.

TBH not shown AP in a good light. Come clutch replacement I will be using another source.

 

[John Vine]

Thanks for the feedback, Andrew.  Do you know whether your cover is the factory-supplied one, or has there been an change/upgrade at some point?   Also, do you know the significance of the -6 and -4 in the nomenclature of the CP3748 family?  There are lots of references on the web to the former but none to the latter. 

The clutch is not designed to run with a pre-load.

That really surprised me when I first read it.  But I'm not familiar with how competition clutches are set up, so it may well be the case.  However, it does raise a couple of interesting questions:

1. What CRB do AP recommend for the CP3748 family of covers?  They state that a flat-face one is needed, but don't quote any part numbers.  From their comment, the CRBs that CC have habitually used for the K (AB57, the INA CRB from the Ford Sierra; or AB57U, the SKF alternative) would both be unsuitable as INA and SKF both state that a pre-load is required. 
    
2. Were CC aware of the AP guidance when they first used the CP3748 cover?

I think pictures always gives them an excuse.

I agree, especially as a trick of the light can suggest markings or wear etc not actually present.  I would suggest that, at the very least, you offer to send the cover, driven plate and CRB to AP for physical inspection and comment.

 

JV

 

 

[John Vine]

If the bearing has the correct pre-load does the bearing face always stay in the same place on the pressure plate fingers - I think not!

According to INA (manufacturer of the CRB that CC originally used), the first use of the clutch centralizes the CRB in relation to the diaphragm fingers, where it subsequently remains.  It is not designed for repeated centralizing.  

I would imagine that, given the arc of travel, the ends of the fingers must trace a short path across the CRB face as the clutch pedal is operated.

JV