Clangy rattle on broken blacktop - Is the CRB mechanism the culprit?

[tompollock]

Eight months in to Caterham ownership and I'm still chasing this illusive clangy rattle coming from somewhere in the middle of the car. It's on a 1700 Supersprint / 5 speed Sierra box / De Dion rear, with 20k miles on the clock.  Apologies for the long thread but I'm running out of ideas.

The clutch (original AFAIK) works perfectly, no slip, good bite point, and the pedal lines up with the brake pedal. Took the rubber boot off the bellhousing and was puzzled (and horrified) to find a good 50mm of rattly slack in the clutch release mechanism before the CRB touched the clutch diaphragm. How long it has been like this I've no idea. Perhaps it had a new clutch some time before I had the car and was never adjusted correctly afterwards.

Shouldn't the CRB be pre-loaded against the diaphragm spring so that it is always spinning at engine revs, or is this particular design/application different from the usual?  Either way do you think the rattly slack in the mechanism, amplified by the acoustics of the bellhousing, is likely to be the source of my clangy rattle, ? Proof of the pudding would be to find a bit of broken tarmac that sets off the rattle, preferably downhill, and drive across it both with the clutch engaged and disengaged.

If I'm right what is the correct amount of pre-load to apply to the CRB when adjusting the clutch cable? i.e. Adjust until the CRB touches the diaphragm, then 1/8th more of a turn on the cable adjustment to pre-load?  Too little pressure and the CRB could get hot spinning against the diaphragm, too much and you could end up overloading the bearing.

Thanks in advance,

Tom.

[Jonathan Kay]

John Vine's Guide: "How to pre-load the clutch release bearing (CRB) for cars with cable clutches".

Jonathan

[Jonathan Kay]

Have you got the warning about checking that the angle of entry of the cable inner to the pedal box doesn't cause excess wear?

Jonathan

[John Vine]

Yes, the CRB should be pre-loaded, and yes, I think my Guide (#2) should help.  Note that my recommended spring CQ13 is no longer available for either CC or Redline, so you'll have to source an equivalent from somewhere.

JV

[tompollock]

Just digesting the replies received so far.  Thanks so much.  Very, very helpful.  I should just add that the engine is dry-sumpted, but it is the after market Neil Brown Engineering one, and I expect the car still has the standard Sierra CRB setup fitted.

[tompollock]

And it's a 1991 car with the Ford Crossflow 1700 Supersprint motor, not that should affect matters.