K-bike forks on an RS?

Discussion in 'Airheads' started by igormortis, Jul 24, 2012.

  1. igormortis

    igormortis Cafe Reise

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    I know I can install these on an airhead frame but - will they line up with the holes in the RS fairing? Will I still be able to fit the rubber bellows?
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  2. wirewrkr

    wirewrkr the thread-killer

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    The fairing booties are going to be the least of your concerns.
    The biggest stumbling block is mounting your instrument cluster. Plus you will need to use whatever fender is called for on the K bike.
    By the way, which K bike front end are we talking about? There are 3 distinctly different ones.
    If you have a twin shock RS, it will look Silly with the Ugly K bike Mag in the front and the spoke wheel in the rear.
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  3. supershaft

    supershaft because I can

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    Monolever forks basically are K bike forks with a slightly smaller tube diameter and different trees. R100R forks are even closer to the same thing depending on how you look at it. Mounting the instruments is a concern but it can be done. It would be relatively easy to run a cross spoke front wheel I believe.
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  4. wirewrkr

    wirewrkr the thread-killer

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    Usually SS I agree with most of what you say.
    On this one I gotta strongly disagree. Just because they use the same axel size, which use the same wheel, That's just not a good comparison.

    The airhead mono lever fork (85-95) was manufactured by Brembo to BMW spec, with 38.50mm fork tubes, a cast aluminum lower triple clamp and a flat steel upper, much similar to the earlier forks to faciltate the same type of instrument attachment, and of course uses a 25mm axel.

    The K bike forks, (all 2 valve K100, pre-93 K75) used a fork also manufactured by Brembo (IIRC) that used 41.50 mm tubes and has simlar, but not identical triple clamps and a 25mm axel.

    The R100R, Mystic and late K75 (93-95) use a fork from SHOWA, a JApanese firm who makes a great product. the tube diameter is 41.00mm, and the trees are cast aluminum, top and bottom. Some countries got the K75 Showa ealier than the USA, a whole year earlier.

    Then we have the K bike front end used on all K100 4 valve and K1100 models, which was manufactured by Marzocchi in Italy. I don't recall the tube diameter, but it is either 41.00 or 41.50 mm.
    These also use a 25mm axel, but once agin that's where the similarity ends.

    I won't even mention the Marzocchi used on the GS and GSPD bikes.

    The important thing is this: Although similar in concept, that's the end of it. They are not "basically the same" as anything but themselves. Implying otherwise would be misleading to those who are just starting out and trying to learn what fits what.

    The 18" cross spoke wheels are hard to find used and usually bring more than the fork set itself.


    The OP still hasn't answered the question of what seies RS he has, so at this point, it's kind of moot.
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  5. supershaft

    supershaft because I can

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    I haven't read all the way through your thread yet but I wanted to say first that I don't mind you disagreeing. Especially since I kind got lazy explaining what I was talking about.

    Agreed so far about Mono forks. Like I said, except for the tube diameter, the FORKS are the same. Same damper rods, sliders, etc..

    That's why I said depending on how you look at it. The R100R forks are basically just like SOME K bike forks. The trees and everything.

    I was wondering about what you were disagreeing with until I got to the 'basically the same' issue. That COULD be misleading. I meant basically the same in form and function but NOT fit. I should have made that clearer. The trees and tubes don't co-mingle well for the tubes being different sizes. It's almost as if they did that on purpose! LOL!
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  6. igormortis

    igormortis Cafe Reise

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    OK - the bike is a monolever, so it already has Ugly covered. I haven’t got the K forks yet - all of them will give me bigger diameter tubes and a top clamp rather than plate - but it sounds like the Showas are the ones to get.

    So, are we looking at a difference in offset also?
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  7. wirewrkr

    wirewrkr the thread-killer

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    I am reverting my Mono lever back to the originals.
    But I ajm adding the billet aluminum upper triple tree from SanJose BMW. (around $120.00) part number 31428.
    They probably have them in stock.
    It's gonna be nice. The stock Mono front end works just fine when adding that bilet triple clamp.
    If you put a Showa on, you will have to get inventive with instrument mounting AND you'll need K bike brake rotors.
    I tried shimming my calipers, but they had such a nasty high frequency squeel, I couldn't stand to ride it. I also didn't like the idea of shimmed brake calipers. That's your life we're talking about.
    I decide to go back closer to stock, and wanted my instruments back so I'm rebuilding the mono forks.
    Make ya a helluva deal on a SHOWA frontend and a pair of low mileage EBC K bike floating rotors though!
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  8. supershaft

    supershaft because I can

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    I have thought about putting Showa's on my bike for some time. After looking at SO many Showa forks with badly pitted and flaked tube chrome, I gave up. Those tubes aren't cheap and they go bad ALL the time on almost every set I see on bikes and off. Compared to German forks, both the Japanese and Italian chrome is JUNK. But the forks work better. It's give and take! The main reason I want some is the teflon bushings in them. Way less stiction! The bushings wear out on a very regular basis too and they aren't cheap either. I recommend changing the fork oil in teflon bushed forks often. I think the bushings last a lot longer doing that. Monolever forks with an aftermarket top tree? There really isn't much of a reason to go for the Brembo K bike forks. Good luck!
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  9. igormortis

    igormortis Cafe Reise

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    Thanks wirewrkr and SS. I think I will try and make my monolever forks work for me. Not happy with them at all at the moment, but it seems some careful measuring and adjusting is in order!

    That deal is tempting, WW - but getting them here to NZ will be another thing again.
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  10. wirewrkr

    wirewrkr the thread-killer

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    Yeah, I know, but I think that triple clamp on your existing is the best way to go, And of course going through the forks and freshening and cleaning.
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  11. supershaft

    supershaft because I can

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    Those Showa's of wirewrkr's are tempting me too igor. I wonder what they were off of originally. I tend to agree about sticking with what you have. After all, that is exactly what I have done although I have a San Jose brace on mine. Get them lined up good and start with about 1/2" preload on stock springs and some 10wt Spectro fork oil. The preload takes some trail and error so get use to that idea before you even get started! I use washers once I am close! Once you are close, the tiniest difference makes a big diff! Good luck!
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  12. Voltaire

    Voltaire Titanium and Ceramic Hipster

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  13. FR700

    FR700 Heckler ™©®

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    '87 my arse . Frame and tank say '84 - early '85 . Black motor may well be '87 .
    Mix and match of various year parts including a k75 spark plug cover plate shown in the pic ' at far right .
    Silver valve cover has oil drain at bottom rear last used early '85 .
    [​IMG]


    .
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  14. igormortis

    igormortis Cafe Reise

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    That guy’s outta his triple tree. I’m sure you could get a sound runner for what he’s asking for that pile of junk.
    #14