Bullshit really does baffle brains doesnt it!!
Sintered bronze has a LOWER coefficient of friction than many other friction materials thus changing to sintered bronze merely reduces the torque capacity within a clutch increasing the slip problem.
The original friction material employed on Commando friction plates was Ferodo MS6. Its C of F values for design purposes are given by Ferodo as DRY 0.34. OIL MIST 0.1-0.12. OIL 0.09. Ferodo also manufactured sintered bronze friction materials. Ferodo SM6 was intended for use with oil and its C of F for design purposes is given as 0.07. Ferodo SM3 especially suitable for dry heavy duty use has a C of F for design purposes of 0.26. The Chief Clutch Designed Of Laycock Engineering (a company that designed and manufactured clutches for much of the USA, European and UK auto industrty and which manufactured all the diaphragm springs used in the Villiers Starmaker, Commando and rotary Norton clutches- 7 different versions in total)) stated to me that for his wet sintered bronze clutch calculations he employed a C of F of 0.06 and stated that the use of 0.08 as given in some reference books was in his experience being optimistic!!
The ONLY reason Villiers and later Norton employed sintered bronze friction material was as a LAST attempt to cdure the serious clutch slip problem due to oil which in turn was due to employing clutches designed to be run dry within an oil bath chain case in the first place!!. In the case of the Villiers Starmaker single and twin friction plate clutches the Laycock Engeineerings Chief Clutch Desiigners (Mr Peter Senior) design note book shows they were originally designed as DRY clutches ...simply because the ******* at Villiers had neglected to inform Laycock Engineering that they were to be employed within an oil bath chain case and were designed to employ either dry use only Ferodo VG or RYZ friction material. Thus they suffered from slip problems due to oil reaching the friction interfaces so rather than redesign everything they simply replaced the friction material with sintered bronze so that when oil entered the clutch resulting in slip problems the slip would generate very high temperatures within the friction interfaces and burn off the oil causing the slip leaving the clutch in theory dry once again...till more oil entered it that is!! Now Norton had exactly the same slip problem due to oil and I suspect that at a mismanagement meeting to discuss possible solutions (they had already changed the diaphragm spring 3 times raising the clamp load from a nice easy two finger operated 380 lbf to a rediculously heavy operated 550 lbf in an effort to cure the slip problem) there must of been an ex Villiers person present who remembered the Starmaker bodge so they suggested they do the same on Commandos......and I bet everyone present ran around screaming ureka as a Greek Gentleman had done a few years previously. The black gunge that forms on Commando bronxe plated clutch friction interfaces causing god awful drag problems is burnt off oil. Friends refer to it as black shit. Personally I refer to Commando so called clutches as vastly overweight gearbox breaking flywheels, especially the bronze plated lumps. Mind you that same applies to Triumph T120 and t140 so called clutches and even BSA A65 ones!! Ever weighed an old Dommy clutch and compared it to later lumps?? Double the weight and you quadruple the mass and the flywheel is suppossed to be on the crank!!
The only possible advantage I can see to employing those RGM bronze friction plates is that the friction material is very narrow compared to other earlier plates thus it increases the effective radius very slightly thus increasing very slightly the torque capacity of the clutch. As to whether the friction material is still directly beneath and in line with the point at which the diaphragm spring applies load to the pressure plate.......... Dont suppose anyone thought about that one.... or did someone ASSUME that the pressure line (the raised lip on the pressure plate) would be in the CORRECT place at the inner edge of the Belliville spring as it was on the Starmaker clutches?? The Commando lumps being simply bodged versions of the Starmaker design.
Go strip a pile of non bronze and bronze plated clutches as I once did with a BIG pile of ex USA clutches a friend bought and you will find every plain plate from bronze plated clutches is badly blued up due to excessive heat due to the rediculous amount of slip they do. mind you I doubt many owners realise their clutches slip every so often or take a lot longer to fully engage.
But I suppose people make money out of flogging the public such clutch plates....... Wonder if the sintered bronze used iwas developed for dry or wet use or both ? I think I know the person to ask.........
