Clutch plates - Pre-Verto types
There are generally three types to be concerned with these days - standard pre Verto, fiber rally/race, and sintered race. All at 180mm diameter.
Standard-type plates. The pre Verto plate has a spring-steel centre section to which is riveted the lining. Between the linings are sprung washers. These take up some of the shock impact of engagement and slight surface imperfections of the flywheel and pressure plate surfaces. Providing a genuine Unipart/AP Lockheed one is used, it will cope with most fast road applications without any problems. This includes almost all road-going standard over-bores (+0.020” to +0.060”) and a vast majority of big-bores (1380/1400). That covers up to 110 bhp and/or 90lb ft. - both flywheel measurements of course!! It is the torque that causes more problems than out-right horsepower. It can also be used in the Verto set-up to improve judder/grip/slip problems experienced when using the 'correct' standard plate. The current standard plate is also what Rover were originally selling as the Metro Turbo plate - so it's pedigree is good. If slip is experienced when using a good ‘blue’ coded diaphragm (see 'Diaphragm Spring - Pre-Verto types' for further information) and the clutch strap set-up is correct (see 'Flywheel - Pre Verto types' and 'Pressure plates - Pre Verto types' for further information), look to using the rally/race plate.
Warning - many after-market non-genuine manufacturers persistently use what can only be described as 'cereal packet' material as replacement friction linings. These will generally cause clutch actuation maladies such as slipping and severe juddering. Buy genuine ones - cheaper in the long run.
Fiber rally/race plate. This possesses a solid centre section, the fiber linings on each side riveted and bonded directly to this. To wit there are no ‘shock absorbing’ properties. Comfort takes a back seat where competition is concerned. The current lining type has evolved from several up-grades by AP Racing over the years where technology and materials have seen constant improvement. In years past a number of other companies have tried to compete - but all failed miserably. Consequently AP Racing has a monopoly on this one. But they are very good, quality consistently high, and price isn’t terrible, and long-lasting. Application is anything road-going above the aforementioned power specs, and race where power levels are not high, limited slip diffs not used, or ludicrously wide slicks. A ‘blue’ coded diaphragm is usually enough for road use. If the engine is pretty serious, then an ‘orange’ coded diaphragm is needed.
Do bear in mind that the stronger the diaphragm used, the heavier the clutch pedal will become. A heavy clutch on a road car - especially if a lot of town driving is done - will become a right pain. Literally.
Sintered plate. The on/off switch type. This is really a race-only item as it is savage by nature. It’s either disengaged or engaged, and that’s it. The nature of the material usually demands a ‘grey’ diaphragm is used to ensure no slip. On lesser-powered, small-bore engines, it is possible to get away with the ‘orange’ diaphragm. But if this is the case, then a fiber plate will probably do. The sintered plate does have the advantage of lasting considerably longer than the fiber one. I really can’t recommend this for anything road going at all. Use the fiber plate and try the increasingly stronger diaphragms to get maximum grip. Something else to bear in mind is the extra heat generated and transferred by using sintered plates. More slip is generally required to get off the line. This generates more heat than the other plates. Some of the heat will transfer into the flywheel and pressure plate, but a percentage will transfer through the plate to the primary gear. This can lead to eventual failure of the bushes (see 'Primary Gear - Bush problems' for further information).
There are plates around manufactured by various alternative manufacturers to Unipart and AP Racing. The only one I can recommend is the sintered plate manufactured by Helix. I have experienced and seen nothing but trouble when any other manufacturers plates have been used. And that covers everything from standard road to full race types. Cheaper they may be, but a seriously false economy in the long run. It ain’t much fun changing a clutch in a Mini with the engine in!!
Useful part numbers:
GCP204AF - Standard clutch plate
C-AHT596 - Rally/Race fiber plate
C-AHT597 - Sintered race plate
GCC103 - Standard 1300 'blue' coded diaphragm
C-AEG481 - 'Orange' coded diaphragm
C-AEG482 - 'Grey' coded diaphragm