YZ 400F clutch drag

[bigk]

We have a '79 YZ400F which has us stumped with clutch drag. All the components have either been checked or replaced, yet it still drags. It will sit on the lie but as soon as revs are taken past idle it drags, and gets considerably worse during the course of a race to the point the clutch doesn't work at all. Any fresh ideas?
Cheers,
K

[TT]

I did have a set of Barnett plates that did a similar thing once. I guess they swelled with heat as when it cooled down it was ok again. Replaced them with the genuine part and all was fixed. That was on a KX250 btw.
Are the plates OEM?

[Viper666]

I know this is no help but I have found this a problem with all my Yamaha for some reason. Some are worse than others.
One thing I have found though is the steel plates need to be perfectly flat & you must adjust the freeplay to its limits, ie just before slipping.
Even brand new plates can be warped, a quick check is to stack them on top of each other, make sure they are clean and dry, and look towards a light.
If you see any between them you're off to a bad start. Some machine joints will do them at cost of course but you then need to compensate for the material lost.
The easiest and cheapest "Try" is change your oil. I use Motul & it's OK but I use it for it's superior gear protection.
Bel-Ray gearsaver is a good one & if all else fails try auto transmission fluid. It is an old trick from the day but I dont know what sort of gear protection it will give.
I can hold my 125 no problems but my 250 I have to put my foot on the back brake to stop it creeping.
I do feel it is the oil that causes most of the problems, given the clutch is in good condition.
One last thing though, if the basket is slight worn and you have filed it the sides must be absolutely parallel.
Sorry another last thing, lay it on its side with the clutch cover off and work the lever, watch that the pressure plate lifts evenly.
I have had brand new springs with different seating pressure causing it to lift high on one side. Sometimes you can just move the springs around to compensate. (6 Spring put the 2 weakest oppisite each other then the next and then the strongest) but other times you just have to buy another set and make one set out of two.

Viper666

[bigk]

Thanks, I'll let you know what fixes it.
Cheers,
K

[lms6201]

check the end float  on the clutch basket bush , assemble the basket and hub without plates and make sure it can rotate freely , i,ve had a few yam clutch assemblies that havebeen a little tite when nutted up tite and when hot thinge have expanded to feel like massive amounts of drag , i think from memory i ground the start gear down a bit to give clearance or i went through the boxes and found a bush a thou or two longer

[Stan S]

We have a '79 YZ400F which has us stumped with clutch drag. All the components have either been checked or replaced, yet it still drags. It will sit on the lie but as soon as revs are taken past idle it drags, and gets considerably worse during the course of a race to the point the clutch doesn't work at all. Any fresh ideas?
Cheers,
K

Hi bigk, have you had a good look at the fingers on your clutch basket to see if there is any wear grooves on the drive side. If there are grooves that can stop the plates sliding evenly causing the plates to cock sideways and drag. You can machine or evenly file the drive side to repair. Also the spring pressures should be even or drag will also occur. Back in the old days with the european bikes we used to shorten the clutch throw lever a bit making the pull a little heavier but allowing the plates to throw further.

Regards Stan.

[bigk]

Problem solved, on closer inspection 2 of the steel plates were incorrect.
Thanks for your efforts.
Cheers,
K