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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Lee Barker on May 27, 2013, 03:39:54 PM
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I've had the K75 a week and gone on a few rides. I am an experienced motorcyclist, but haven't ridden much in the last 7 years or so.
When I hid an abrupt unevenness, say, in the pavement, I really feel it in my hands. It doesn't feel like there's much shock absorption going on in the front.
I checked my Clymer's (thanks Dan for including that in the sale) and read that front travel is about 7 3/4". Off the centerstand, lunging the bike ahead and applying the front brake gives me an apparent 5 inches of travel, very stiff.
Is this normal, and one of those things we adjust to, or might there be something changed or awry in the tubes?
Your experience will be appreciated.
Kindly,
Lee
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Total travel would be from no weight on the front to complete compression. Standing still I doubt you could achive it short of getting about 500-600lb on the front end.
You don't want to bottom out because once it bottoms things start to bend.
Put a zip tie around the fork in the travel zone. Not real tight but tight enough that it doesn't slide without influence. It will serve as a marker for maximum travel. Ride a couple days and I'm pretty sure you will see the front exceeds 5 in of compression.
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I've had the K75 a week....
You might want to change out all the fluids in the bike, including the fork oil.
The Motobrick Library is a great resource as is this link: http://www.verrill.com/moto/newkbike.shtml (http://www.verrill.com/moto/newkbike.shtml)
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greetings lee barker...
if it were me i would be thinking aftermarket fork springs on down the road... butts for now like tim tyler said i would drain the forks and add new suspension fluid...
stock is 7.5wt butts most motobrickers go to the honda shop and score 2 bottles of the honda ss8-10wt suspension fluid (http://www.chaparral-racing.com/Product/pro-honda-suspension-fluid-ss-8-10w/19-1024.aspx)...
different motobricks take different amounts... even each fork tube can take a different amount... click here to see for yourself... (http://www.ibmwr.org/ktech/fork-oil.shtml)
i use a flavour injector (http://www.walmart.com/ip/Mainstays-Flavor-Injector/14964956) to add the fluid at the top of the forks... no needle... just stick it in there... go slow...
if you do the change... ride it and get the suspension fluid hot... then let it drain overnight... you can use aluminum foil or plastic sheeting to keep the fluid off the brake disk... i use gallon zip lock bags tapped to the fork and drain the fluid right into the bags... your o rings are easy to lose and your plugs are easy to strip...
j o
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Welcome Lee,
You don't mention what year K75 you have but the shock brand changed in 1992 which also means the amount of fork fluid needed changed. I found out the hard way that some manuals are confused about the date of the change and the previous mechanic put the volume needed for the other brand of shock rather than for the Showa which mine is. Once I drained the old fluid and put the correct amount of new in, my ride improved dramatically.
And, as Johnny says, new progressive springs should help even more, but I'm still waiting for that to happen.
HTH.
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Be careful not to strip the threads on the fork legs when re-installing the small drain screws, OR to not to strip the heads on the hex bolts hidden by the axle on the fork bottoms if you drain the fluid that way.
The second option will allow you to remove the lower forks and clean out any sludge in there if you have the time.
Both options require fresh crush washers only available from dealer.
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Thank you Grim, Tim, Johnny and Wayne. Excellent info.
It is a '94, and thanks for the caution on the data.
I think I will contact the seller, a nice guy, and see if anything has been done to the front recently. That will guide my next moves.
I just finished removing the Givi brackets which came with the bike--alas no cases--and I am thoroughly impressed with the engineering of that particular product.
And, amazingly enough, I am left with a question: Obviously on the left side there are two bolts which hold the muffler to the wing-like casting which bears the rear sets. On the other side, mirror image casting, same two holes--are they there for weight reduction, or do they have a special purpose not obvious to me?
Thanks for your more help.
Kindly,
Lee
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perhaps oem bags z bars...
peg plates... (http://www.2wheelpros.com/oem-parts/1990-1995-bmw-k75-k569-footpeg-plate-footpeg-assembly.html)
z bars... (http://www.2wheelpros.com/oem-parts/1990-1995-bmw-k75-k569-set-case-holder-assembly.html)
photos please...
j o
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A survey of web images didn't get much of an answer so I'm relying on MotoBrick UberGoogle.
BTW, I don't think the future of civilization as we know it clings to the outcome of this inquiry. I am just toying with making my own little frames for saddlebags and I'm scouting for attachment points.
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Yeah - Those are for the OEM racks.
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When I first got my 1985 K100RS, I thought the front was way too soft. everytime I hit the brakes the front will dive. Every bump I hit, the front will sink and wallow. After replacing the fluids for a heavier weight (1ow) and added probably more than I should 360ml each side when the range I think is 330-360ml, the rife firmed up a bit.
From your description, I think you're trying to say your forks are too hard, stiff and not very giving which is exactly opposite of my problem initially. I think most people prefer too stiff over too soft. My understanding of fork tuning (love to hear other people's feedback also) is that a lighter weight oil will give you more dive. Also less volume of oil thereby giving more air in the tubes will lead to more dive and soften the fork some. Progressive springs will firm up the ride some. But still, being able to compress the front by 5 inches just by pressing sound like a lot and opposite of what I would expect from a fork that's too stiff. Fork oil is relatively cheap and I would play with different weight and volume to see if you can find a something to your liking.
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Compromised fork travel could be from a part failure in one or both of the fork legs.
Or, the p.o. used a too much or a heavier than recommended fork oil.
BTW SAE does not apply to fork oil. That is to say that a 10wt is not the same between brands.
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I used atf tranny fluid once......it actually works great......Think I had it in for a half season.......til I got the real stuff.......( My dad said there wasn't much of a difference cept being red)
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When I got my bike, a K75RT ex-police it had Fichtel and Sachs front forks. Sometimes referred to as S forks. A strange design with only one fork leg actually acting as a damping unit, the other one "neutral". By neutral I mean it's just traveling in bushings without any damping mechanism at all. Both legs have similar springs though and the same quantity of oil.
I didn't like these S forks, short travel and harsh ride. Changing to lighter weight oil didn't improve things much. A German friend suggested I swapped them out with the later Showa forks of "conventional" design and with longer travel. This turned out to be a great improvement, the Showa forks are much better and easy to adjust by changing the oil weight. I use 7 weight oil, just blended 5 and 10 half and half. Suits me fine