K11 Owners Group

[gerard]

I have recently changed the rubber boot on the clutch arm at the rear of the gearbox (approx 2 weeks ago). The new part has now torn but also appears to have melted. My question is; is there meant to be a heat shield between the boot and exhaust or is my bike running hot? [/b]
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The on-going resurrection of a nearly flying brick!

[hfxrzw]

Did some oil come out of the boot or the recess? The bearing in the clutch operating rod would need some lubrication otherwise could get hot with regular clutch use
_________________
Cheers, Rene

Greetings from Florida.

BMW K100 '85

[gerard]

Hi Rene,

I was to go over to Scotland for a bike trip at the start of the month but the boot split the evening before the boat! No oil is leaking at stand still but i could smell it burning coming home from work today. Think she is going to be off the road again until i order part from Motobins. Cheers
_________________
The on-going resurrection of a nearly flying brick!

[Ernie-NH]

Hi Gerard...

The "boot" is a rubber compound and cannot melt like plastic. It can however 'disintegrate' or revert to 'gum' ( like all rubber parts ) if exposed to solvents or hot oil based compounds.. Is this the same boot that was "dripped" on when you had the transmission fluid too high ?? These boots are made from Chloroprene ( CR ) and are only moderately resistant to Transmission fluid, and that only at temps up to 100 degC. Also check the 'grease' that you used, tell me what it is ( brand name ) and I will look it up to check CR resistance to that particular grease.. You dont want to have a repeat experience...

Good luck......// Ernie in NH
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[hfxrzw]

Ernie, I don't understand you comment. There is supposed to be transmission oil in the boot in order to keep the thrust bearing of the clutch operating rod lubricated. Are you telling us that BMW has used material for the boot that is not resistant to transmission fluid?
_________________
Cheers, Rene

Greetings from Florida.

BMW K100 '85

[Ernie-NH]

Hi Rene...

NO... its probably temperature related, or its an "aftermarket" boot from some inferior compound. Chloroprene ( ie: Neoprene ) is only moderately resistant to Transmission fluids at best, and really bad when exposed to synthetics. A better choice would have been a Nitrile, but even that is not best, Hytrel which is actually a thermoplastic elastomer would have been a proper solution... but since that boot is NOT actually filled with fluid, but rather there to contain seepage, it culd survive IF temps remained below the 100/120 degC level, and the boot is NOT pressurized. ( ie: the questionable fit of the boot at its smallest diameter and the pressure clamp at its greatest diameter is NOT a design that is meant to contain a body of fluid that must constantly be refreshed ) My best GUESS is that failure of the boot in that area is first related to excessively high temperature "in/around" the boot itself, second is the original choice of compound by BMW, and thirdly the questionable choice of materials by some possible unknown "aftermarket" supplier to both BMW itself and to us the rider/mechanics. However, without actually having a failed boot in my possession, I can only offer conjecture as to the cause of failure. I will say with certainty however, that when BMW Autobereich was a customer of the firm for which I worked in Germany, I had the pleasure of many many many arguments with them relative to materials and elastomer design in general, and can never once remember coming out of top in such discussions.... I have no reason to suspect that BMW Motorradbereich is any different then or now..

Best regards and good luck....// Ernie in NH
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AMA,, American Deaf Bikers
Airhead Beemers Club
'11 G650gs
'95 K1100LT
'76 R100/7

[Ernie-NH]

Hi Rene...

NO... its probably temperature related, or its an "aftermarket" boot from some inferior compound. Chloroprene ( ie: Neoprene ) is only moderately resistant to Transmission fluids at best, and really bad when exposed to synthetics. A better choice would have been a Nitrile, but even that is not best, Hytrel which is actually a thermoplastic elastomer would have been a proper solution... but since that boot is NOT actually filled with fluid, but rather there to contain seepage, it culd survive IF temps remained below the 100/120 degC level, and the boot is NOT pressurized. ( ie: the questionable fit of the boot at its smallest diameter and the pressure clamp at its greatest diameter is NOT a design that is meant to contain a body of fluid that must constantly be refreshed ) My best GUESS is that failure of the boot in that area is first related to excessively high temperature "in/around" the boot itself, second is the original choice of compound by BMW, and thirdly the questionable choice of materials by some possible unknown "aftermarket" supplier to both BMW itself and to us the rider/mechanics. However, without actually having a failed boot in my possession, I can only offer conjecture as to the cause of failure. I will say with certainty however, that when BMW Autobereich was a customer of the firm for which I worked in Germany, I had the pleasure of many many many arguments with them relative to materials and elastomer design in general, and can never once remember coming out of top in such discussions.... I have no reason to suspect that BMW Motorradbereich is any different then or now..

Best regards and good luck....// Ernie in NH
_________________
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Airhead Beemers Club
'11 G650gs
'95 K1100LT
'76 R100/7

[gerard]

Hi Ernie,

The boot was subjected to quite a bit of oil, i.e. it could not have got any more saturated if I had dropped it in a bottle of oil! The grease is anyones guess, came in a white tube, no markings from garage so I assume it was correct. New parts on order, again!
_________________
The on-going resurrection of a nearly flying brick!

[Ernie-NH]

Good morning Gerard.. Good morning Rene...

You know, I dont want to "beat a dead horse" here because this "boot" is such a simple matter,,, first it was never meant to contain any fluid(s) but rather as a simple exclusionary device as are almost all rubber boots of this type. The K bike clutch is a dry clutch design and there should be NO FLUIDS inside the boot itself other than perhaps some grease from the push rod, an even then a bare minimum. IF you (Rene) find any fluid in the boot then you have a far greater problem than the boot itself... As far as the material "reversion" ( ie: the gummy disintegration )as found on Gerard's boot, that is most certainly a result of the transmission fluid degrading the compound, and accelerated further due to the high temp in/around the boot.

It is not uncommon for even BMW to designate elastomeric materials that are marginal or even inappropriate for the "end use", but in BMW/Engineering defense, it is most often the Purchasing Dept that compromises the best designs in favour of cost reduction, as it is with all automotive companies. Despite that, the design of this application has been done with no consideration for further simplicity. The very fact that a large and unnecessary 'ring clamp' is used, ignores the cost and difficulty of such a clamp when a simple 'groove' in the casting and a 'retainer bead' on the inner diameter of the boot would accomplish the same function with ease and at a reduced cost. As you examine your bikes component designs, I am sure you will think of many ways that YOU would have designed it to make the mechanics job simpler and the components design more functional.. BMW does NOT have a monopoly on "clever" !!

Wishing you both well, ride safe wherever you are....// Ernie in NH
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'95 K1100LT
'76 R100/7

[hfxrzw]

Ernie, my understanding is that the clutch rod bearing area is in connection with the clutch housing, allowing prevention of air pressure in the boot when operating the clutch. It seems rather normal for some oil to reside in the booth (I haven't seen one dry), otherwise why fit a seal on the rod?
_________________
Cheers, Rene

Greetings from Florida.

BMW K100 '85

[Ernie-NH]

Hi Rene...

The "clutch area" should be a completely dry assembly... if by "seal" you mean the 'O-ring" behind the small retainer nut, thru which the clutch rod passes, it is there only to prevent the axial ingress of "clutch dust" which would otherwise build up and create drag on the free sliding of the rod. The only lubrication between that o-ring and the outer boot is the grease on the 'flat face" ball bearing under the 'pressure piston' and the light surface grease on the surface of the rod itself.

With reference again to the 'outer boot', the small diameter is merely 'hugging' the end of the 'clutch arm' and any pressure that builds within the boot during compression will simply "fart" its way out and conversely 'suck' air in again when the piston within forces it back out ! You mentioned that you have 'fluid' inside your boot,,, that disturbed me, so I went to look inside the 'clutch lever boot' on my "K" and find it dry and residue free !! Because my "R" bike has a nearly identical setup, I checked that boot as well and find no internal moisture, or oil, or in fact fluid of any kind,,,so I cannot even guess at this point where the moisture in your case is coming from. If you are concerned about it, and decide to track to down, PLEASE let us all know what you find...

Very best regards..........// Ernie in NH
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'11 G650gs
'95 K1100LT
'76 R100/7

[Scott_Anderson]

I'd beg to differ with you a little bit there Ernie on the boot.
There is a small flat roller bearing(for the clutch rod) behind the boot that has to be lubricated to a degree or it's not going to last long.
When I have taken both of mine apart for various reasons they have had trans oil in them. If yours is dry I'd be finding out why.
The o-ring on the push rod is to prevent the oil from migrating up the rod to the dry clutch area.

There should be enough space and protection that the boot shouldn't be subject to excess heat from the exhaust. I have heard of more issues with rocks getting stuck between the clutch lever and the trans housing causing problems.

There are 2 small roller bearing that the clutch lever rotates on that should be lubricated too. A little moly 60 does wonders.
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Ride safe.



1995 K1100LT 0302044
2017 FLHTK Ultra Limited
Garmin StreetPilot 2820
Garmin Zumo 550
Garmin Zumo XT
"One who does not ask questions is ashamed to learn" Danish proverb
1997 K1100LT 0302488(R.I.P.)
1997 R1100RT ZC62149(sold)

[Ernie-NH]

Hi Scott..

I both agree and disagree with you on this point. Yes there has to be grease for the "flat face" ball bearing, and Yes there has to be surface lube only on the rod since it is still rotating while the clutch is being engaged, BUT No on the oil entering into and up the rod channel. The rod is centered on/along and through the axis of the trans-input shaft true, BUT there is an oil seal on both ends of that shaft to to preclude the transfer of fluid exiting the transmission proper, the smaller of two at the rear should prevent any fluid from escaping into the rod chamber between the o-ring nearest the clutch and the "flat face" bearing location, spring piston etc... In short, there should be no transmission fluid entering into that chamber. In fact, the boot being chloroprene is not intended to come in contact with any form of transmission fluid or general gear oils. Quite the opposite to being dry, would be very worried if I find any form of fluid passing up the rod and into the boot interior, and would regard such as a precursor to failure.

Best regards..........// Ernie in NH
_________________
AMA,, American Deaf Bikers
Airhead Beemers Club
'11 G650gs
'95 K1100LT
'76 R100/7

[hfxrzw]

Ernie, with respect, I think we have to agree to disagree. If the 'clutch rod seal' (and that's what it is, a proper seal ring, not a flimsy boot) was fitted for prevention of dust build-up and subsequent difficult operation of the clutch, than why would the forward end be running in a brass bush without protection? And why isn't it fitted in the forward end instead of the aft end? I'm not worried about some transmission oil in the boot. Mine has it, some of the bikes I worked on had it and it is a regular returning post on all the BMW K forums, referring to torn boots noticed due to oil leakage.

Anyway, on to riding these great machines! Just did a trip over the weekend through Scotland; beautiful when the sun shines!!!! Even a bit when not.
_________________
Cheers, Rene

Greetings from Florida.

BMW K100 '85

[Ernie-NH]

Hi Rene...(et al)..

Glad your visit was a sunny success! I have only seen Scotland from the windows of a train or hotel, and have never had an opportunity to visit there other than on business. The "economy" being what it currently is, I will probably never again have the chance. Thats why "riding pics" are important to so many of us that will never get the chance to visit such far away places.

One LAST note on the "boot situation".... Everyone has an opinion on how something either 'works' or does 'not work' and thats what makes discussions such as these so interesting... To my knowledge however, there is no transmission engineer that would introduce a design that allows fluid to escape under any circumstance, and the transmission is NOT a location for a seal that allows a controlled leak... in short,( ie: IMHO) IF fluid is leaving the transmission and finding its way back to a simple boot that is meant ONLY to be an exclusionary device, then the design has failed. I can tell you from personal experience, neither ZF nor Getrag, the two companies that make the majority of BMWs transmissions, would ever allow a design that tolerates leakage... I assume the "k" bike transmission is no exception. In this situation, Scott ( who has vastly more experience with this particular application than do I ) feels the leakage is acceptable, whereas I as a seal designer having worked with both ZF and Getrag for many years, contend that it is not. So there you go....

At any rate, ride safe, have fun, and enjoy your beautiful country as well...

Best regards..........// Ernie in NH
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AMA,, American Deaf Bikers
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'11 G650gs
'95 K1100LT
'76 R100/7

[kstones]

Hi Gerard;
i can't imagine how the rubber boot would have melted!! It is between the back of the gearbox input shaft bearing support and the actuator arm; between the boot and the exhaust system is the pivot base struture that the actuator arm rotates on via the pivot rod. If the boot melted so would the mudguard, the battery vapour pipe, the tyre? Seems very odd.
The boot is to provide a seal to keep in the gearbox oil which splashes around the rear end of the input shaft and lubricates (as well as everything else) the circular thrust bearing on the back end of the clutch push rod; this oil cannot get along the input shaft as an oil seal is fitted to its end through which the push rod passes. the boot also keeps outside dirt from getting into the gearbox. The oil level in the gearbox is only slightly below the input shaft so there will a lot of oil around; it may be even level with it for i remember getting oil leaking out of the K75 when i was replacing a boot - others may advise on this, but you can be sure there is plenty oil around when the engine is running to lube all the input shaft etc.
A new boot correctly installed will last you many miles; i've had to do one in 60000 miles; make sure the boot is right on onto the gearbox input shaft rear end protrusion and the jubilee clip is really tight ; and the actuator arm is nice and clean where the outer end of the boot goes over it.
good luck
Tony.