The clunk these bikes make when going into first has from day one made me cringe. How can all this good engineering have embraced this clutch? The sounds a bike make are part of the experience. How much do we pay attention to our exhaust note? The clunk is the sound of crashing metal. But this bike is exhilarating to ride. But you have to get past first. Hereís what Ií e been working on.
A few givens here, this is a 2009, K1300R, upgraded oil pump and a K1200 slave cylinder, 32mm. A new given is a pause after disengaging the clutch before dropping into first. No need to pause with any other gear but first. This pause allows the steels to shed oil that otherwise will cause fluid coupling and the clunk. Patience is rewarded. I need to put more time into riding the bike now. There are inconsistencies in how long a pause is needed. I think Iíve added a new bit of personality to this bike. If I find myself in a sentimental moment, I can forgo the pause and the clunk resurfaces as a reminder that the new personality is worthy of embracing.
At this point I will just give an outline of the problems and the solutions I found dealt with clutch issues. For most K owners what I have come up with is beyond what many would want to do or have an interest in. Many of these bikes have made it past 100000 k with no complaints. Also my approach is likely not the the only way. I can certainly give the details if anyone wants to go there. Some may just be interested in understanding the aspects I have looked at in this clutch. I do wish BMW had made the hub maybe a mm taller. That would be a 50% increase in the space for the plates when disengaged. It would have offered the plates more shoulder room and less drag. Oil we can manipulate, hub space is set at the casting plant for the hub.
First there is the issue of oil. Everywhere it has been stated there is not enough oil being delivered to the clutch. I would ask, how did this get established? The early K1200 did have issues with wear and oil. BMW never seems to have put the resources needed into fixing this clutch. They circled around the peripheral, different oil holes, anti-judder setup, anodized basket, steels with dimples, changing the thickness of the steels, the four variations of the thrust adapter, a higher capacity oil pump (really just a change in sprockets), a change in specified oil, these changes were over a number of years. Cynicism whispers in my ear, they needed to give dealers something to show BMW was working on this. Being told ĎThey all do thisí is to normalize a defect. I bought into this with the upgrade to the oil pump. It may have been the right thing to do. I have nothing else to compare it to. This is the pump Iíve done the exploration with.
Oil distribution within the clutch is a big problem. What ever pump or thrust adapter the pattern is, to varying degrees, the same. Very oil soaked plates near the hub going to dry plates towards the middle of the pack, then uneven near the pressure plate. Those very oil soaked plates contribute to the clunk. With this bike there is way too much oil being delivered to the clutch. An amount that will always cause fluid coupling.
I filled all the oil holes in the hub. Through trial and error I settled on size of hole and pattern. I think this could be improved, but itís very time consuming. To give an idea about how much of a change, take the holes at the hub that deliver oil to the hub and anti-judder setup. OEM hub has two holes that are about 3mm, close to an 1/8Ē in diameter, 180 degrees apart. I settled on one hole that is 1/16Ē. Sorry my drill set is imperial. Even with that reduction there seems to be plenty of oil at the hub.
The architecture of the hub does not lend itself to even oil distribution. Itís like the designer of the hub and the person who decided where and how large the oil holes were to be, never knew what the other was up to. Just looking at the hub one can make valid assumptions and predictions about the short comings.
Next was to reduce the amount of oil on each steel surface. The goal is a relatively even oil film throughout. This I did first with the oil hole size and multiples and then by grooving the steels. In big commercial clutches grooves are most commonly done within the friction material. Some do groove the steels. I had zero confidence I could do this in the frictions. So grooves in the steels help shed oil. As the friction pads slide over a groove, it acts like a windshield wiper pushing the oil into the channel and draining off the plate through release from the centripetal force.
At this point there was little consistency in overcoming the drag/fluid coupling. I started thinking what would be nice is a two level of oil delivery. A good oil flow when the clutch was engaged and a lesser flow when disengaged. Oil in these clutches preform three functions, lubrication, cooling and flushing wear out of the clutch. I did come to realize this clutch does have two level delivery. The two slots in the thrust adaptor are where oil is delivered. The exposure of these slots is shortened by the amount the slave moves the slotted pin into the transmission shaft. But the effect is not really noticeable. I started putting washers of different thickness on the slotted pin between the transmission shaft and the thrust bearing. Effectively shortening the exposure when engaged and significantly reducing oil flow when disengaged. An improvement, yes, but still erratic.
The clutch plates were not separating consistently. This clutch relies on a completely passive way for the plates to separate, simply, the pressure plate moving away from the clutch pack. I kept the Ďanti-judderí setup because it provided some active plate separation with the Belleville spring. BMW had at one time introduced those green o-rings to help push the plates apart. They used them on three frictions 180 degrees apart and altering every other friction. I expanded this to five plates with o-rings on successive frictions. Instead of stacking these o-rings as BMW did, I offset these o-rings in a spiral. The spiral shifts the pivot point the friction plate rocks on its O-rings from its neighbours rocking point. Sort of encourages more random jostling of the plates which helps break the fluid coupling'. Thatís the idea anyway. By saying offsetting the O-rings, I mean in plan view each successive friction, the tab with the O-ring shifts, in this case counter clockwise by two tabs.
I understand many will be wary of reduced oil in the clutch. My confidence was raised with some reading up on synthetic oils. What they offer is really very impressive. The reliable thickness of the oil film is much reduced compared to conventional oils. Secondly, these oils behave in a non Newtonian way. I had to read up on this. Under heat and pressure synthetic oils become almost solid, might be more like a wax. This produces a very slippery surface that has filled the hollows and valleys of the steels. The anticipation here is wear on clutch will not be increased by a reduced oil film.
Lastly, I am not an engineer or mechanic. I used the same route and stopping points for every test run. I did have to lengthen the run when I realized how long it takes the oil to get up to its running temp. Because I was interested in the disengage state of the clutch, I always held the clutch lever in for about 5 seconds and shut off the bike while disengaged. The clutch pack was on the bench in about 12 minutes.
I will keep an eye on wear. At this time, the hub and pressure plate look to have a clean oil film and more oil than any of the internal steels. At one time in this exploration the oil on the pressure plate was sooty looking, too much pressure while disengaged. I found the pressure plate oil delivery method to be very passive and indirect, a bit like crossing your fingers and hoping . It really has little to do with the way oil is delivered to the rest of the clutch pack.
Finally, this clutch is called a wet clutch. Once I started going in the opposite direction from this clutch needing more oil, I began to consider it more an oil mist clutch. Still classed as wet clutch but oil mist frames the idea of how this clutch works better.
I put a video on YouTube 2 months ago showing a diminished clunk. I was still working towards consistency. It is still audible but not as harsh, I canít feel it through the bike. The second video, most recent, has almost no sound going into first. I have to partially let the clutch out while in first to show it is actually engaged. The first link is the earlier video. The second link is the most recent one.
For anyone wanting a good overview about the K1200 and K1300 clutch, go to YouTube and look up Patrique Hofmanís technical review of the K1200 2008 clutch plates and basket. He has a number of videos about these bikes and they are all very informative.