So I've just picked up a MK3 850 (1976) after it had been in a dry garage for 20 years, have got it running fine and MOTed but the clutch slips as you feed it in (between gear changes going up) have just taken it apart and the 5 friction plates are all down to 3.1mm thick and the the steel are slightly polished, My question is what is the service tolerance on the friction plates ?
Many thanks
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The rest of the bike will…
The rest of the bike will rust away before the bronze plates wear down, they have a service life approaching a million miles!
Assuming the clutch is in good condition (center not notched etc)
Wash the plates in a suitable degreaser and reassemble, expect to do it again annually or every 5000 miles, dont overfill the pri drive case, bike on side stand when filling to level plug hole, use ATF oil.
ensure pri drive case is not getting g/box oil or engine oil leaking into it. 20 yrs stood the seals might have gone hard so drawing oil into the case.
If still having problems the bronze plates can be machined to reduce there area so increasing grip.
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The ATF oil Peter recommen…
The ATF oil Peter recommends for the clutch is perfect for the clutch and what I use on my MK2A with bronze plates but some MK3 primary chain adjusters take too long to regain prime on it after a lay up and the chain slaps around for too long. In which case you have to use the thicker recommended 20/50W but if you can use it then the ATF is preferable as its designed for auto boxes with multiple clutches and resistant to slipping.
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yeah got bronze plates in…
yeah got bronze plates in there and they look fine so will do as you say and de-grease them then put ATF in the primary
many thanks for the info
Regards Martin
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Welcome -- searching the site with "Slipping clutch Commando" will bring up more advice than you can shake a stick at.