Well, after the chicken menace wiped any post of mine a few months ago, I reposted any things that might be of some value except the juicy original post at http://drriders.com/topic6143.html . Since I consider this a simple money saving tip that can be applicable to many guys trying to figure out their slipping clutch troubles, I repost it here afresh as good as I remember the data as I cannot remember exactly what my original post was.
So your clutch is slipping more and more at ever less engine load as mileage accumulates while commuting in hot Summer days?
Or you got caught up at some nasty low speed trail and you had to slip you clutch overtime and now it slips big time, all the time?
First things to check are the obvious ones: Clutch cable slack and free moving as a tight spot could be the reason for intermittent slippage - what? You already checked this and all good?Before you reach for your wallet and order a new clutch set, measure your clutch pressure springs located on the clutch pressure plate.
Suzuki claims their working length is good down to 33mm (1.3inch) free length. Well ... nope!
What I found hands on in two occasions is that slippage starts before this limit even while the clutch plates themselves are well within service thickness and have not been burned up. I had quite a lot of slippage close to WOT at 33.3mm and big time slippage (unable to go over 70km/h) at 32.9mm free spring length.
So check them along your existing clutch plates before
buying a new clutch set. Friction plates may have long life still in them so no need to get new ones, just new (and better) clutch springs! (...or as Plonker has suggested, some shims could do the trick if you cannot get clutch springs but I have not tested this).
I got the bike with about 100 000 Kms. The donating friend and previous owner was using it as an everyday city commuter and general on-off traveler riding most of the time 2-up with his wife. At 70 000 km or so, he had replaced the worn out original clutch set with a pretty much unused second hand clutch set and this is what I got the bike with. Right from day one at my hands it was just slipping at WOT on high speed tarmac stretches. During the next 24 or so months I used the bike for about 12 000 more city kms and the slippage progressively worsened during hot congested city heavy hand
use of mine. Not to the point that the bike was unrideable and I took this CVT alike behavior to good use against stronger bikes in between traffic lights drag races downtown tight Athens city boulevards. I tried to fight the problem with top of the self Motul and other full synth oils to clear possible friction plate smudge but no change - had no time to properly repair this as it was my main vehicle and could not afford any possible screwup of mine and no proper expert service.
However things worsened to the point it needed fixing but at the same time I left the big city life behind for the rural mountains I now live and the bike stood still for months expecting my wallet health to improve since I was sure it would require new clutch plates. I discovered a nearby breaker who had a similar XF650 Freewind engine and he was willing to sell me the looking good clutch set and springs for cheap. So I dismantled my DR's clutch only to find out that the XF's looking good plates were in about the same condition to my existing clutch plates - only the clutch pressure springs were found longer at 34.2mm vs mine in-service-limit 33.3mm.
So I put in there the XF's good set (police bike rear ended), the XF's springs, the cheapest 10W-40 oil in the market and go for a spin on a 30C day. The clutch feels and behaves perfectly so I go try an unknown uphill trail. The trail gets tighter and tighter and my dead stock engine stalls easily so a lot of clutch use is in order to avoid this. Things get hot quite fast and I start to feel the clutch slipping again worse and worse in a few hundred meters. I barely make my way back to the tarmac and the clutch feels completely toast: Just holding 20-30 kph on the tarmac uphill and 70-80kph on the straights slipping like crazy on the tinniest throttle opening. All this in less than 16kms, yeap 10 miles after this long awaited repair
It certainly got hot as I had plastic parts of my boots melting on the clutch cover
so I was sure the clutch was toast for good. Nicely baked color, isn't it?!
A few days pass and I discover that the previous owner between various other stuff had also supplied brand new looking OEM clutch springs that measured at least 35mm long (maybe 35.5?)
So I decide to look into my clutch again and to my surprise I see the XF's friction/metal plates in pretty much the same condition I put them there - only the oil got cooked and smudged. Since they were 0.1mm thinner than the DR's plates I took out, I put a mix of the 2 sets based on scientific criteria (which plates shined best on the sun) and the brand new springs I discovered. Do a couple of cheapo oil flushes and went for a ride with the same cheapo oil.
And ... all good! I still have this setup for the last 1500 or so kms and it behaves flawlessly! Mixing two slipping clutch sets should be a recipe for a slipping clutch again, shouldn't it? Well, not! Just have pressure springs long enough! How long? Hmm, let me guess here since other factors as the big concave washer spring must be taken into account as well (I changed it and not measured any possible deformation) and how polished the discs are due to wear. I suppose that 34mm should be considered a safe service limit for OEM springs - adding numbers from whatever memory is a bit fuzzy and I cannot give a solid number for sure surfacing from my experience.
What I was astonished to find out was that a nice 2nd hand 34.2mm OEM spring shrunk to just 32.9 mm over less than 500 meters of heavy continuous slipping to get through a very tight trail in a Summer day. Was totally sure I fried the clutch plates but nope: Cheapo spring material a.k.a. Suzuki cheapo. Talk about cutting corners from the production process! Damn bean counters!